Solid sensor

Abstract

Solid sensors for measuring various physical parameters are described herein. The solid sensors can be used in systems, devices, and methods for controlling blood flow or measuring (e.g., monitoring) blood pressure. In some instances, the method can include obtaining a first count number indicative of the oscillation frequency in a first ring oscillator circuit during a sample period. The first ring oscillator circuit can be associated with the sensor and oscillates at a first oscillation rate. The first oscillation rate can be based on a first set of physical parameters and a second physical parameter. The method can further include obtaining a second count number indicative of the oscillation frequency in a second ring oscillator circuit during the sample period. The second ring oscillator circuit can be associated with the sensor and oscillates at a second oscillation rate. The second oscillation rate can be based on the first of the physical parameters but may not be based on the second physical parameter. The method can further include determining a value associated with the second physical parameter in the sensor based on the first count number and the second count number.

Description

Technical Field

[0001] (Cross - reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 346,286, filed May 26, 2022, the entire content of which is incorporated herein by reference.

[0002] (Field of the Invention) The devices, systems, and methods herein relate to sensors that can be used to measure parameters including, but not limited to, pressure.

Background Art

[0003] Sensors can be configured to measure various physical properties. For example, a Wheatstone bridge sensor can include a piezoresistive circuit on a silicon - based die and can be configured as a pressure sensor or a strain gauge.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, piezoresistive sensor measurements are affected by inherent resistor offsets and inherent temperature offsets, and these offsets can be mitigated by an offset compensation circuit that may include one or more of a differential amplifier, potentiometer, digital-to-analog converter (DAC), analog-to-digital converter (ADC), and resistor. Further, the wires coupling the sensor to the electronic circuit can have a length (e.g., 500 mm or more) that functions as an antenna picking up common-mode noise. Differential low-pass filters and differential amplifiers can be used to provide high common-mode rejection for the wires. The circuitry required to compensate for sensor offsets and wire noise increases the cost, size, weight, and manufacturing complexity of the sensor. Accordingly, additional devices, systems, and methods for measuring parameters may be desirable.

Means for Solving the Problem

[0006] Described herein are systems, devices, and methods that include sensors useful for measuring one or more parameters (e.g., physical characteristics), including but not limited to pressure (e.g., blood pressure). In some variations, the sensor can be part of a device for controlling blood flow, such as one or more of a sensor proximal to an expandable member (e.g., a balloon), a sensor distal to the expandable member, and a sensor within the expandable member. In other variations, the sensor can be included in a device that measures pressure (e.g., blood pressure) without controlling blood flow. One or more sensors can be used to measure one or more parameters. For example, multiple sensors (e.g., two, three, four, or more) can be used to measure the same parameter, each of the multiple sensors can be used to measure a different parameter, or some of the multiple sensors can be used to measure the same parameter and some of the multiple sensors can be used to measure different parameters. Each sensor can be housed within its own sensor housing, or multiple sensors can be housed within a single sensor housing. In some variations, the sensor housing that houses one or more sensors can be integrated into an elongate body (e.g., a catheter), as described in more detail herein. In one variation, the sensor includes a first circuit configured to receive an input clock signal and output a first output clock signal having a predetermined ratio between the input clock signal and the first output clock signal using an adjustable delay, a second circuit configured to receive the input clock signal and output a second output clock signal using an adjustable delay, and a third circuit coupled to the first circuit and the second circuit and configured to generate a third signal based on a difference between the first output clock signal and the second output clock signal.

[0007] In some variations, the first output clock signal can vary based on a first set of parameters, and the second output clock signal can vary based on a second set of parameters different from the first set of parameters. In some of these variations, the first set of parameters can include one or more of temperature and voltage. In some of these variations, the second set of parameters can include one or more of temperature, voltage, and resistance or capacitance corresponding to force, pressure, optical amplitude, acoustic amplitude, and chemical or physical reactions.

[0008] In some variations, the third signal can correspond to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude. In some variations, the frequencies of the first output clock signal and the second output clock signal can each be greater than the frequency of the input clock signal. In some variations, the first circuit can include a first plurality of delay circuits arranged in a ring configuration. In some of these variations, the first plurality of delay circuits can include a first plurality of inverter circuits and a first adjustable delay circuit. In some of these variations, the first adjustable delay circuit can include a rate counter. In some of these variations, the first plurality of inverter circuits can be coupled to a first multiplexer. In some of these variations, the first plurality of inverter circuits can be configured within a closed loop with positive feedback.

[0009] In some variations, the first delay circuit can include a first resistor-capacitor delay circuit. In some variations, the second circuit can include one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit. In some variations, the first circuit can include a first oscillator circuit.

[0010] In some variations, the fourth circuit may be coupled to the third circuit, and the fourth circuit is configured to receive an input clock signal and output a fourth output clock signal using an adjustable delay. The third circuit may be configured to generate a fifth signal based on the difference between the first output clock signal and the fourth output clock signal. In some of these variations, the fifth signal may correspond to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude.

[0011] In some variations, the substrate may include the first circuit, the second circuit, and the third circuit. In some variations, the first substrate may include one of the first circuit and the second circuit, and the second substrate may include the other of the first circuit and the second circuit.

[0012] In some variations, the fourth circuit may be configured to output the third signal as a digital signal. In some variations, the fourth circuit may be configured to output the third signal as a set of binary-coded bits at a periodic rate. In some variations, the fourth circuit may include one or more of a wire and an antenna.

[0013] Also described herein is a method for measuring a parameter, the method including receiving an input clock signal, generating a first output clock signal having a predetermined ratio between the input clock signal and the first output clock signal using an adjustable delay, generating a second output clock signal using an adjustable delay, and generating a third signal based on the difference between the first output clock signal and the second output clock signal.

[0014] In some variations, the first output clock signal may vary based on a first set of parameters, and the second output clock signal may vary based on a second set of parameters different from the first set of parameters. In some variations, the first set of parameters may include one or more of temperature and voltage. In some variations, the second set of parameters may include one or more of temperature, voltage, and resistance or capacitance corresponding to force, pressure, optical amplitude, acoustic amplitude, and chemical or physical reactions.

[0015] In some variations, the third signal may correspond to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude. In some variations, the frequencies of the first output clock signal and the second output clock signal may each be greater than the frequency of the input clock signal.

[0016] In some variations, the fourth output clock signal may be generated using an adjustable delay, and the fifth signal may be generated based on the difference between the first output clock signal and the fourth output clock signal. In some variations, the fifth signal corresponds to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude.

[0017] In some variations, the third signal may be output as a digital signal. In some variations, the third signal may be output as a set of binary encoded bits at a periodic rate.

[0018] Also described herein is a sensor that includes a first ring oscillator circuit oscillating at a first oscillation rate. The first oscillation rate may be based on a first set of physical parameters and a second physical parameter. The sensor may further include a second ring oscillator circuit oscillating at a second oscillation rate. The second oscillation rate may be based on the first of the physical parameters, but may not be based on the second physical parameter. The sensor may further include a first rate counter circuit that is operably coupled to the first ring oscillator circuit and configured to count a first oscillation number in the first ring oscillator circuit during a sample period. The sensor may further include a second rate counter circuit that is operably coupled to the second ring oscillator circuit and configured to count a second oscillation number in the second ring oscillator circuit during a sample period. The sensor may further include a circuit configured to receive representations of the first oscillation number and the second oscillation number and, in response to receiving the representations of the first oscillation number and the second oscillation number, generate a value associated with the second physical parameter in the sensor based on the first oscillation number and the second oscillation number.

[0019] Also described herein is a sensor. The sensor includes a first ring oscillator circuit that oscillates at a first oscillation rate. The first oscillation rate may be based on a first set of physical parameters and a second physical parameter. The sensor may further include a second ring oscillator circuit that oscillates at a second oscillation rate. The second oscillation rate may be based on the first of the physical parameters, but may not be based on the second physical parameter. The sensor may further include a first rate counter circuit that is operably coupled to the first ring oscillator circuit and is configured to count a first oscillation number in the first ring oscillator circuit during a sample period. The sensor may further include a second rate counter circuit that is operably coupled to the second ring oscillator circuit and is configured to count a second oscillation number in the second ring oscillator circuit during a sample period. The sensor may further include a communication circuit that is configured to send representations of the first oscillation number and the second oscillation number to a processing circuit operably coupled to the communication circuit, and in response to receiving the representations of the first oscillation number and the second oscillation number from the communication circuit, cause a value associated with the second physical parameter in the sensor to be generated based on the first oscillation number and the second oscillation number.

[0020] Also described herein is a method that includes obtaining a first count number indicative of an oscillation number in a first ring oscillator circuit during a sample period. The first ring oscillator circuit may be associated with a sensor and may oscillate at a first oscillation rate. The first oscillation rate may be based on a first set of physical parameters and a second physical parameter. The method may further include obtaining a second count number indicative of an oscillation number in a second ring oscillator circuit during the sample period. The second ring oscillator circuit may be associated with the sensor and may oscillate at a second oscillation rate. The second oscillation rate may be based on the first of the physical parameters, but may be independent of the second physical parameter. The method may further include determining a value associated with the second physical parameter in the sensor based on the first count number and the second count number.

[0021] Also described herein is a method that may include measuring a first value of a first parameter using a first sensor, transmitting the first value to a second sensor coupled to the first sensor, and measuring a second value of a second parameter using the second sensor. The method may further include generating a serial value that includes the first value and the second value.

[0022] Devices configured to monitor a patient's physiological state or to adjust physiological parameters (e.g., blood flow or blood pressure) are also described herein. These devices may include any one or more of the sensors described herein integrated into an elongated body (e.g., a catheter). In some variations, one or more sensors may be configured to measure blood pressure. When the sensor is included in a blood flow control device, the balloon may be coupled to the elongated body and configured to be disposed within a blood vessel. One or more sensors may be housed within a sensor housing that may protect the sensor from damage caused by body fluid (e.g., blood) or pressurization from the balloon of the blood flow control device. The sensor housing may be formed from any suitable material, such as a polymer, metal, or metal alloy. In some variations, the sensor housing is made of stainless steel. In other variations, the sensor may be fully or partially encapsulated within a polymer within the sensor housing.

[0023] Additionally, devices configured to monitor blood pressure are also described herein. The device can include any one or more of the sensors described herein that measure blood pressure and are integrated into an elongated body (e.g., a catheter). The one or more sensors can be housed within a sensor housing as described above to help protect the sensors from damage caused by bodily fluids (e.g., blood) or other external factors. In some variations, the sensor and / or the sensor housing can be tubular in shape and can have a diameter of about 1 Fr. The sensor can be fully or partially encapsulated in a polymer within the sensor housing. When the sensor is coupled to a PCBA (Printed Circuit Board Assembly) housing, the housing can include an adhesive configured to attach the PCBA housing to the patient's skin. The adhesive can optionally be provided as an adhesive patch.

Brief Description of the Drawings

[0024]

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DETAILED DESCRIPTION OF THE INVENTION

[0025] Described herein are systems, devices, and methods for measuring parameters (e.g., physical properties) including, but not limited to, temperature, voltage, force, pressure, light amplitude, and sound amplitude. For example, in some implementations, the systems, devices, and methods described herein may include sensors configured to measure changes in electrical propagation time (e.g., delay) corresponding to physical properties. The sensors may be coupled to a computing device (e.g., a microcontroller) configured to receive an output from the sensors, determine a measurement value of the parameter, and optionally output (e.g., display) the measurement value and / or send an indication of the measurement value to another computing device. The sensors may be disposed within a sensor housing to help protect the sensors from damage due to fluids (e.g., blood) and / or other external elements. The sensors may be housed, positioned, and / or encapsulated within the sensor housing and integrated into an elongated body (e.g., a catheter) used in various devices, such as blood flow control devices and pressure monitoring devices, as further described herein.

[0026] The systems, devices, and methods described herein may substantially compensate for changes such as temperature, voltage, silicon skew, common mode noise, etc., and may be particularly useful for medical, automotive, aerospace, and industrial applications where there are size and / or weight constraints. In contrast, conventional PLL multipliers require complex analog modeling of the silicon process and generally have problems at specific combinations of silicon temperature, voltage, and / or speed. However, conventional compensation solutions, such as additional circuit elements including differential amplifiers, differential low pass filters, offset compensation, and analog to digital converters (ADCs), are not required for the systems, devices, and methods described herein.

[0027] Sensor Generally, the sensors described herein may include a plurality of compensated ring clock multipliers (e.g., oscillator ring circuits) configured to generate and output an accurate higher speed clock signal from a slower speed clock signal. An adjustable delay may be calculated for the output clock signal of a first oscillator ring circuit corresponding to a first set of parameters (e.g., temperature, voltage, silicon die). A second oscillator ring circuit may be configured to generate and output a second clock signal that varies in response to the first set of parameters and at least one additional parameter (e.g., pressure). The difference between the output clock signals corresponds to a measurement of a sensed parameter (e.g., pressure) that essentially compensates for the first set of parameters (e.g., temperature, voltage, silicon die). Additional oscillator ring circuits may be used to measure additional parameters. Further, in some variations, the measured parameter may be output as a digital signal that increases resistance to electrostatic discharge.

[0028] Figures 1A, 1B, 2A, and 2B illustrate a conventional sensor and various limitations and drawbacks thereof with respect to the invention described herein. Figure 1A is a schematic diagram of a conventional Wheatstone bridge sensor 100 (e.g., a pressure sensor, a strain gauge) including resistors R1, R2, R3, and R4 coupled to a voltage source V and a voltage measurement circuit. As shown in Figure 1A, R1 and R2 form a sensor element (e.g., a half Wheatstone bridge), and resistors R3 and R4 have fixed resistances. For example, a change in pressure corresponds to a change in R1 and / or R2. For example, an increase in pressure may correspond to an increase in R1 and a decrease in R2. In particular, pressure is proportional to the differential voltage across the bridge voltage V BC When R1 is equal to R2 and R3 is equal to R4, the voltage V BC is 0V, and the current through R1 and R3 is the same as the current through R2 and R4. However, when R1 and / or R2 changes (e.g., due to a change in pressure), the voltage V BC increases or decreases accordingly and can be measured by the voltage measurement circuit. Then, the change in pressure is related to V BCIt can be measured based on

[0029] In some variations, the conventional Wheatstone bridge sensor separates R3 and R4 from the sensor elements R1 and R2. Further, R3 and R4 can be set to have resistance values as close as possible. For example, V BC As long as R3 is equal to R4, R1 does not have to be equal to R3 as long as V depends on the ratio of R1 to R2. However, when R3 is not equal to R4, V BC may include an error (e.g., an offset). This offset can be measured and used to calibrate the sensor (e.g., when the sensor is manufactured or turned on). For example, the sensor can be calibrated by measuring V BC at first and second predetermined pressures. The inherent offset and gain of the sensor circuit can be determined using linear regression so that the sensor can be calibrated.

[0030] Similarly, R1 and R2 do not have to have any particular relationship in any one state. For example, under ambient pressure, R1 can be 2000.5 ohms and R2 can be 2002.1 ohms, and when R3 is equal to R4, V BC may not be 0V. However, the inherent offset can be removed in pressure measurements as long as another measurement is made at a different pressure.

[0031] FIG. 1B is a schematic diagram of another Wheatstone bridge sensor 150, where sensor elements R1 and R2 are further away from the rest of the circuit. For example, when used in a blood flow control device such as an intravascular balloon catheter, R1 and R2 can be inside the body and can be about 50 cm to about 100 cm away from the rest of the circuit (e.g., V, R3, and R4). For example, a Wheatstone bridge circuit configured as a pressure sensor preferably has dimensions smaller than the diameter of the body lumen (e.g., artery, vein) in which it is placed. In some variations, the pressure sensor can include R1 and / or R2 and a set of wires (e.g., three wires, namely, wires from V to R1 and R2, a wire from R1 to R3, and a wire from R2 to R4) to connect to the rest of the elements of the circuit disposed outside the patient. Further, the voltage and / or current applied to the pressure sensor can be relatively low to reduce heat and patient risk in case the sensor and / or wires are damaged. For example, resistors R1 - R4 can be about 2K ohms, and the voltage applied to the pressure sensor can be about 2V to about 5V such that the current is less than about 1 mA. For these values, the differential voltage V BC can vary between about 10 μV / mmHg to about 20 μV / mmHg per 1 mmHg change in pressure. A voltage measurement circuit having a resolution of less than about 5 μV can be configured to provide a pressure measurement resolution of about 0.25 mmHg. However, an amplifier configured to amplify by more than about 200 times is typically required.

[0032] However, when used in this configuration, for example, in a blood flow control device, the length of the wire can reduce sensor accuracy. For example, the wire can function as an antenna that picks up both common mode noise and differential noise. Conventionally, removing this common mode noise requires a common mode low pass filter, and even with this filter, a differential amplifier with a high common mode rejection ratio may still be required. Further, a differential low pass filter is typically used to filter the differential signal before it is input to the differential amplifier, so the wires are generally not matched. Even so, the low pass filter itself can add a very low frequency offset, a phase delay in the signal, and attenuation at higher heart rates that must be compensated for in software.

[0033] Conventional sensors can be affected by different offsets that can reduce measurement accuracy. In some variations, a conventional sensor can include an offset compensation circuit that includes one or more of a differential amplifier, a potentiometer, and a DAC configured to compensate for the inherent offsets introduced by R1 and R2. However, even an offset compensation circuit can add a small gain error to the measured value. Further, silicon-based sensors can be sensitive to temperature changes. For example, a 1°C change in temperature can correspond to a change in offset greater than 1 mmHg. In some variations, the offset compensation circuit can include one or more of a circuit configured to individually measure the respective voltages V B and V C a resistor, and an ADC configured to measure the current of the entire Wheatstone bridge. The design and implementation of the offset compensation circuit can result in additional cost, size, weight, and manufacturing complexity.

[0034] Figure 2A is a schematic block diagram of a sensor used within a medical device that includes several electronic devices inside the body and several electronic devices outside the body. The piezoresistive MEMS sensor can be conceptualized as the incorporated R1 and R3 (from FIGS. 1B and 1C), and R2 and R4 are implemented within a circuit mounted on a small printed circuit board (PCB).

[0035] Solid state pressure transduction (SSPT) circuits such as those shown in FIG. 2A are known, but there are several limitations. For example, one limitation relates to balancing the bridge. In addition to R2 and R4, the small PCB must also be adjusted to obtain a default value of VOut within the range such that it is within the capabilities of the amplifier and analog-to-digital converter (ADC). For example, if the value of VOut at 0 mmHg pressure is too high, at higher pressures (such as 200 mmHg), the output of the amplifier can be larger than the output that the ADC can measure. If the system is one that measures negative pressure and the amplifier and ADC are simplified to avoid measuring negative voltages, the value of VOut will be greater than 0 at the lowest pressure. During manufacturing, the potentiometers can be adjusted such that VOut is relatively small at 0 mmHg. Even with these potentiometer adjustments, additional offset adjustments using active circuits such as those within a chip like the PGA309 can be used to compensate for variations due to different atmospheric pressures, handling of negative pressures, and other variations that occur at other stages of the manufacturing process. These characteristics can affect the manufacturing cost and test cost of the SSPT.

[0036] Another limitation is due to power supply and ground noise. The Wheatstone bridge configuration is susceptible to the effects of electrical noise on the V-Exc signal that supplies current to R1 and R3 (as shown in FIGS. 1B and 1C). Any noise on that line can result in a corresponding change in VOut. Similarly, when the electrical ground shifts, the asymmetry in the stray capacitance and resistance can result in a significant change in VOut. Further, along the path, the amplifier and ADC may not have the same response to a shift in the supply voltage or ground, and thus these voltage changes may appear as noise in the measured value.

[0037] Another limitation is due to electrical noise on the long wires within the catheter. The wires can act as unintentional antennas, and the 50 - 100 cm wires within the catheter may have an undesired amount of gain over a wide range of frequencies. The energy captured by the wires (aka, antenna effect) changes the intended value, and this change is referred to as "noise". The noise can be dynamic and can have frequencies ranging from a few Hertz (Hz) to hundreds of millions of Hertz. This type of noise is generally known as Radio Frequency (RF) noise. Specifically, the 60 Hz alternating current (AC) power currently used in the United States and the 50 Hz AC currently used in Europe can result in particularly high noise levels.

[0038] As shown in Figure 1B, the excitation voltage (V-Exc) is directly coupled to the resistors R1 and R2 of the Wheatstone bridge. If electrical noise (e.g., variations) is picked up on the V-EXC wire, this has the same effect as power supply noise. If the noise is picked up only on the SIG+ or SIG- wires, this also directly changes VOut. If the same noise is picked up simultaneously on both the SIG+ and SIG- wires, this generates "common mode" noise. An ideal differential amplifier ignores this noise because theoretically it does not change the difference between the voltages on SIG+ and SIG-. However, in reality, the various resistances and capacitances along the two paths are not identical, and this common mode noise to the amplifier results in a difference.

[0039] As a result of the noise limit, often a set of filters is used. A first differential filter is often used before VOut is given to the amplifier. This filters out some of the high-frequency common mode noise and differential noise. Next, another low-pass filter is placed after the amplifier. This cuts the high-frequency noise that "aliases" the noise to a lower frequency at the ADC. Finally, a digital low-pass filter is sometimes used in software to remove any noise captured by the ADC.

[0040] Some of the electrical noise can be difficult to filter, such as that seen in the use of a general emergency electrical surgical pencil and defibrillation. Regulatory authorities are aware of this limitation, and specifications such as 60601-1 and 60601-2-34 allow a recovery time after the large noise has disappeared.

[0041] Another limitation of SSPT relates to runtime calibration. When SSPT is used, there can be variations in the voltages supplied to the sensors, amplifiers, and ADC chips. These variations can be due to changes in the temperature of these circuits. They can also be due to variations in the output of various power supplies, especially those powered by batteries. The sensors can also have variations with respect to temperature. For this reason, additional circuitry and manufacturing costs are often required to compensate for changes due to temperature.

[0042] Another limitation of SSPT relates to interoperability. In a REBOA catheter that has SSPT sensors above and below the balloon and a display unit outside the body, it may sometimes be desirable to make the catheter itself interchangeable so that a single display unit can be used with multiple catheters. Since calibration has to be performed on the entire analog circuit (sensors within the catheter and electronics within the display unit), the interchangeable "boundary" has to be at the ADC. This may require separate chassis for the analog and digital circuits, adding further cost.

[0043] FIG. 2B is a schematic block diagram of a conventional analog path for sensor 200, such as a Millar sensor that may have a relatively small differential voltage change per mmHg. For example, sensor 200 may have a 2.74V excitation of a Wheatstone bridge with a μV / V / mmHg change corresponding to 13.7 μV / mmHg. Amplification in excess of 200 times may be required to achieve sufficient resolution to enable the use of a 3.3V ADC. The offset compensation circuit may include a PGA309 chip configured to compensate for the offset and adjust the gain so that the output is within a predetermined range of the ADC. The systems, devices, and methods described herein address the drawbacks in the prior art.

[0044] I. Sensor Systems and Devices A. Advantages over Known Technologies The sensors described herein can offer many advantages over conventional sensors that use, for example, a known Wheatstone bridge. Examples of these advantages include, but are not limited to, the following.

[0045] First, the sensors described herein (e.g., pressure, force) can utilize a MEMS circuit configuration in which analog-to-digital conversion can be performed directly on the sensor die. In some variations, rather than having a very small differential voltage as an output, the sensors described herein can generate a digital output (e.g., a serial digital stream), such as a universal asynchronous receiver transmitter (UART), that can be easily read directly by a computing device, such as an off-the-shelf microcontroller. Second, the use of the sensors described herein can reduce manufacturing costs, system size, and system power, and can allow for increased flexibility in the way devices that utilize these sensors (e.g., medical devices) are prototyped, designed, and manufactured. Space and power consumption can be important considerations for some of the devices brought into harsh settings. The development of fully digital pressure sensors, such as those described herein, greatly simplifies the backend electronics for these devices. For example, at least in some variations, since the sensors described herein can use power and a precision clock as inputs, the computing device can be significantly simplified compared to known techniques (only circuits that receive power, a clock source, and a serial message (e.g., UART), receive it either wired or wirelessly, and convert it into a wired or wireless format). Thus, in some variations, the display can be separated by any distance. Also, since the sensor is essentially always in an "output mode" (not a read response mode), the output value can be sent to two or more computing devices.

[0046] Third, as will be discussed in more detail herein, the sensors described can provide a digital output (e.g., a serial digital stream indicative of pressure), which can enable detachment of the device portion from an external electronic device (e.g., in the context of a medical device having an elongated body such as a catheter, catheter shaft, etc.) so that the electronic device can be used with multiple devices. Further, the sensors described herein also enable replacement of a portion of the electronic device in the event the electronic device is damaged and / or the power supply is disconnected. In a variation where the sensors described herein are utilized within a medical device (e.g., a blood flow regulation device), the portion of the medical device advanced into the patient can remain within the patient while the external electronic device (e.g., a computing device) is being replaced.

[0047] Fourth, the sensors described herein can provide a higher quality digital output than conventional Wheatstone bridge sensors that provide an analog signal. For example, particularly with respect to use in pressure sensing applications, the digital output can have a noise tolerance that is at least 10,000 times greater than, for example, an analog signal. As an example, if the digital output is nominally 3.3 V for a logic 1 and 0 V for a logic 0, the receiver can, for example, tolerate a noise level of 1 V and still be able to distinguish between 1 and 0. In an analog-based Wheatstone bridge, a noise level of just 100 microvolts can correspond to a change in the pressure reading of as much as 4 mmHg. This can be too large an error for high-fidelity physiological monitoring that can form the basis of medical devices. Additionally, the digital messaging scheme increases signal fidelity by allowing for the addition of error detection bits that can further improve the reliability that the received message is not corrupted. Additionally, in some variations such as where a computing device receives a digital value, the temperature of the computing device may have little or no effect and compensation or calibration may not be required for the circuit that generates the digital value. Also, having a digital output from the sensor can eliminate the amplification stage previously used for an analog solid-state pressure sensor or with a fluid column-based pressure sensor. Without an analog amplifier, there is also no need to match the voltages between the amplifier and the associated ADC.

[0048] Fifth, in some variations, the sensors described herein utilize sensor wires that are resistant to RF inductive noise or are less likely to be affected by RF inductive noise. For example, the sensors described herein can utilize sensor wires that are smaller (e.g., <0.1 mm) than conventional sensor wires, and thus the sensor wires can be small enough to not be affected by RF inductive noise.

[0049] Furthermore, having only digital signals that cross long wires eliminates the need for almost all low-pass filters. This can save space on the sensor circuit, reduce complexity, and / or do similar things.

[0050] Sixthly, the sensors described herein are readily adaptable across various silicon processes compared to known techniques, thus enabling them to be versatile across processes.

[0051] Seventhly, the sensors described herein can provide improved fault detection compared to conventional sensing techniques. For example, if any of the sensor wires are damaged, the computing device (e.g., microcontroller) can detect the fault within a short time frame (e.g., 1 sample period) since the digital output from the sensor stops.

[0052] Eighthly, the sensors described herein can easily enable the use of various runtime diagnostics by changing the input clock rate or by changing the supply voltage, which is not possible with many conventional sensing techniques.

[0053] There are many advantages to using the sensors described herein, but there can also be challenges when creating sensors with built-in analog-to-digital converters (ADCs). For example, it may be desirable for the ADC to add a minimal size to the silicon die so that it still fits within the size constraints of the device for specific applications, such as within the elongated body of a medical device. In some implementations, the sensor die may be located at least 50 - 100 cm away from the power source, so it may also be desirable for the sensing element and the ADC to be resistant to voltage changes. Also, for example, it may be desirable for the ADC to be resistant to changes in the location of the sensor (e.g., inside a patient's body) or temperature.

[0054] Some known analog-to-digital conversions are performed using sigma-delta techniques or successive approximation techniques. This may require complex circuitry that must be adapted to each silicon process and may be sensitive to operating voltage and temperature. Some variations are shown with respect to FIGS. 11A and 11B and, as will be considered, use an approach for essentially generating a digital output from an analog sensor measurement. For example, some variations use a set of oscillator rings, a set of counters and latches, and some mathematical calculations to perform analog-to-digital conversion, as will be considered in more detail herein.

[0055] B. Sensor System Generally, a sensor system can include one or more of the components necessary to measure and optionally output parameters using the systems described herein. A block diagram of an exemplary solid state sensor system 300 is depicted in FIG. 3. System 300 can comprise one or more of sensor 302, controller 320 (e.g., a device controller, a microcontroller), and computing device 340. In some variations, sensor 302 can be coupled to one or more of controller 320 and computing device 340 via a network (e.g., via a wired or wireless connection). Sensor 302 can be configured to measure one or more parameters (e.g., temperature, voltage, force, pressure, light amplitude, sound amplitude, radiation). The measured parameter can correspond to any parameter capable of varying the time delay of a delay element. For example, one or more of resistance, capacitance, and inductance can be varied in response to a change in the parameter. In some variations, the measured parameter can be based on another circuit (e.g., a resonator) coupled to an oscillator ring such that the measured parameter is based on a secondary approach. In some variations, system 300 can be configured to output sensor measurements via controller 320. For example, controller 320 can be configured to output a digital signal (e.g., of the measured parameter) to computing device 340 without analog-to-digital conversion. In this way, system 300 can be formed without an ADC, which can reduce one or more of the size, cost, and manufacturing complexity of system 300.

[0056] Returning to FIG. 3 and referring thereto, in some variations, the sensor system 300 may comprise one or more of the sensor 302 and the controller 320. The sensor 302 may comprise one or more of a first circuit 304, a second circuit 306, an optional third circuit 308, an optional fourth circuit 310, an optional rate counter 312, an optional delay calculator 314, an optional latch 316, an optional divider 317, and an output device 318. In some variations, one or more of the first circuit 304, the second circuit 306, the third circuit 308, and the optional fourth circuit 310 may comprise a ring oscillator circuit as described in more detail herein. In some variations, the divider 317 may include one or more sets of circuits configured to divide an input signal (e.g., convert a 32768000 Hz clock to a 16384000 Hz clock). In some variations, the counter 312 may include one or more sets of circuits configured to count the number of oscillations (i.e., ticks) in the first circuit 304, the second circuit 306, the third circuit 308, and / or the fourth circuit 310 during a sampling period. In some variations, the latch 316 may include one or more sets of circuits configured to store a representation of the count captured by the counter 312. In some variations, the output device 318 may be configured to transmit a signal indicative of the count captured by the counter 312 and / or stored in the latch 316. In some variations, the output device 318 may include a shift resistor, an output resistor, and / or a serializer, etc.

[0057] The controller 320 may comprise one or more of a processor 322, a memory 324, an input device 326, an output device 328, and a communication device 330, each of which is described in more detail herein. In some variations, the system 300 may be disposed on a single substrate (e.g., a single die) or on multiple substrates. For example, the sensor 302 may be disposed on a first substrate and the controller 320 may be disposed on a second substrate.

[0058] In some variations, the input device 326 may be configured to receive signals based on a set of output clock signals from the sensor 302. In some variations, the output device 326 may be configured to output data associated with the system 300 as a digital signal. In some variations, the processor 322 and the memory 324 may be configured to control the sensor system 300. In some variations, the communication device 330 may be configured to communicate with one or more components of the system 300 and the computing device 340 (e.g., a mobile phone, a tablet, a laptop, a desktop PC). In some variations, the computing device 340 is a microcontroller.

[0059] FIG. 3 shows the computing device 340 as separate from the controller 320, but note that in some variations, the controller 320 and the computing device 340 may be a single unit (e.g., a single chip).

[0060] In some variations, multiple sensors may be coupled to each other. For example, in some variations, multiple sensors (two, three, four, or more) may be coupled in series with each other (i.e., daisy chained). In these variations, the clock rate may be modified to account for the daisy chained sensors. As an example, if a 32,768 Hz input clock is used to measure values from a single sensor, the clock rate in the daisy chained variation may be the number of sensors daisy chained multiplied by 32,768 Hz (e.g., using a 65,536 Hz clock if two sensors are daisy chained, using a 98,304 Hz clock if three sensors are daisy chained, etc.). Additionally, as shown in FIG. 14B, an input may be added to a serializer (i.e., shift resistor) that receives bits from an upstream sensor. Thus, a digital output (e.g., a UART-type serial output) may report values from multiple latches within multiple sensor chips to a computing device. In some variations, multiple sensors may be read using just four wires to / from the computing device, with the power, ground, and clock wires each coupled to all sensors, and the output of each sensor coupled to the “shift in” of the subsequent sensor until the last sensor in the chain generates a digital output that may be coupled, for example, to the UART input of the computing device.

[0061] An example of a daisy-chain connected sensor is shown in FIG. 14A. The first sensor 1402 can measure a first value, and the first value can be provided (e.g., as an input to its serializer) to a second sensor 1404 that can measure a second value. The second value can be provided (e.g., as an input to its serializer) to a third sensor 1406 that can measure a third value. A digital output (“SER OUT”), which is a serial list of each value measured by each of sensors 1402, 1402, and 1406, can be generated. In some variations, each value measured by each sensor is concatenated to the input provided to that sensor's serializer (when the input is provided to that sensor). For example, “SER OUT” can be a list of bits indicating a bit representing the value measured by sensor 1402, followed by a bit representing the value measured by sensor 1404, followed by a bit representing the value measured by sensor 1406. In some variations, each value measured by each sensor is distinguished from other values measured by other sensors using a known indicator such as a predetermined combination of bits known to the processor. “SER OUT” can then be provided to a computing device configured to identify each value measured by each sensor using “SER OUT”. Sensors 1402, 1404, and 1406 can all measure the same parameter (e.g., pressure), all measure different parameters (e.g., pressure, force, light amplitude), or can be a combination of some sensors measuring the same parameter and some sensors measuring different parameters. As shown in FIG. 14A, the daisy-chain of sensors can have only four wires, namely, voltage (VCC), clock (CLK), serial output (SER OUT), and ground (GND). In one example, the sensors can be disposed inside a human, and the four wires can be connected to a computing device (e.g., a microcontroller) further away from the sensors (e.g., 50 - 100 cm away), and can be configured to determine each value measured by sensors 1402, 1404, and 1406.Using a similar variation as in FIG. 14A can enable a single UART to read multiple sensors and can significantly reduce the total number of wires for wiring within a system having many sensors (for example, because instead of each sensor having its own SER OUT, only one SER OUT is provided for multiple sensors).

[0062] FIG. 15 shows a top view, a side view, a front view, and a perspective view of an exemplary chip. Chip 1500 may include sensors. As shown therein, chip 1500 may include a plurality of wire bond pads 1502 positioned on a complementary metal-oxide semiconductor (CMOS) bare die 1506. More specifically, chip 1500 may include one bond pad each for voltage, clock, serial output, and ground, four bond pads, and wire bond pads 1502 may be positioned on the top surface of CMOS bare die 1510. Chip 1500 may further include a sensor delay, i.e., a micro-electromechanical system (MEMS) piezoresistive sensor die 1508. The MEMS piezoresistive sensor die 1508 may be configured to delay the oscillation frequency by one or more ring circuits based on the parameter being measured (e.g., pressure). Chip 1500 may further include a CMOS circuit 1504 that may include the remaining sensor components (e.g., oscillator ring, latch, counter, serializer). In some variations, as contemplated herein, chip 1500 may be disposed within a sensor housing. In some variations, the CMOS bare die 1506 may have a width of about 200 microns to about 500 microns, a width of about 250 microns to about 450 microns, a width of about 300 microns to about 400 microns, a width of about 330 microns, a width less than 200 microns, and / or a width greater than 500 microns (including all values and subranges therein). In some variations, each wire bond pad from the wire bond pads 1502 may have a width of about 20 to about 100 microns or about 30 to about 90 microns (including all values and subranges of any of the above), and / or a length of about 150 to about 250 microns or about 175 to about 225 microns (including all values and subranges of any of the above). In other variations, each wire bond pad from the wire bond pads 1502 may have a width less than 20 microns, a width greater than 100 microns, a length less than 150 microns, and / or a length greater than 225 microns.In a further modification, the CMOS circuit 1504 may have a width of about 200 to about 300 microns or about 225 to about 275 microns (including all values and sub-ranges of any of the above), and / or a length of about 50 to about 150 microns or about 75 to about 125 microns (including all values and sub-ranges of any of the above). Alternatively, the CMOS circuit 1504 may have a width less than 200 microns, a width greater than 300 microns, a length less than 50 microns, and / or a length greater than 125 microns. In a further modification, the MEMS piezoresistive sensor 1508 may have a width of about 200 to about 300 microns or about 225 to about 275 microns (including all values and sub-ranges of any of the foregoing), a length of about 500 to about 700 microns or about 550 to about 650 microns (including all values and sub-ranges of any of the foregoing), and / or a height of about 200 to about 300 microns or about 225 to about 275 microns (including all values and sub-ranges of any of the foregoing). In some modifications, the MEMS piezoresistive sensor 1508 has a width less than 200 microns, a width greater than 300 microns, a length less than 500 microns, a length greater than 700 microns, a height less than 200 microns, and / or a height greater than 300 microns.

[0063] In some implementations, a sensor (e.g., included in chip 1500) can be incorporated into an application-specific integrated circuit (ASIC). For example, FIG. 16 shows a block diagram of an exemplary sensor 1600 incorporated into an ASIC. As shown therein, sensor 1600 can include a plurality of wire bond pads 1606 (e.g., four wire bond pads) similar to wire bond pads 1502 depicted in the sensor of FIG. 15. These four wire bond pads can be operably coupled to digital logic 1604 configured to oscillate a plurality of rings and count the oscillation frequencies for each of these rings. Sensor 1600 can also include a MEMS piezoresistive sensor 1602 configured to delay the oscillation frequency in the first oscillation ring (but not in the second oscillation ring) via a resistor based on the parameter value to be measured.

[0064] a. Oscillation circuit Generally, an oscillator circuit (e.g., a compensated ring oscillator) described herein can be configured to receive an input clock signal and generate an output clock signal having a frequency greater than the frequency of the input clock signal. The oscillator circuit can include one or more (e.g., a plurality of) delay circuits (e.g., inverter circuits such as Schmitt trigger inverters) arranged in a ring configuration. The oscillator circuit can be configured to generate an output clock signal having a predetermined ratio (e.g., the output clock signal is an integer multiple of the input clock signal) by compensating for inherent circuit offsets such as temperature and voltage by adjusting the delay of the oscillator circuit. Suitable circuits for use in the systems, devices, and methods herein are described in Patent Document 1, which is hereby incorporated by reference in its entirety.

[0065] FIG. 4 is a schematic diagram of an exemplary variation of an oscillator circuit 400 comprising a plurality of delay circuits 410 and an adjustable delay circuit 420 arranged in a ring configuration, a rate counter circuit 430, and a delay calculator circuit 440. The circuit 400 is configured to receive an input clock signal and generate an output clock signal having a predetermined ratio between the input clock signal and the output clock signal using the adjustable delay circuit 420 calculated by the delay calculator circuit 440. The adjustable delay circuit 420 may be configured to set a predetermined delay based on the calculated adjustable delay. That is, the adjustable delay may be calculated by comparing the ratio of the output clock signal (e.g., ring frequency) to the input clock signal and adjusting the adjustable delay to a predetermined ratio. In some variations, the adjustable delay circuit 420 comprises one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit.

[0066] The rate counter circuit 430 may be configured to count the number of output clocks generated for each single count of the input clock. The delay calculator circuit 440 may be configured to calculate the difference between the output of the rate counter circuit 430 and a predetermined ratio.

[0067] The frequency of the output clock signal may be greater than the frequency of the input clock signal. In some variations, the plurality of delay circuits 410 may be coupled to a multiplexer (not shown). In some variations, the first plurality of inverter circuits may be configured in a closed loop with positive feedback. In some variations, the oscillator circuit 400 may be disposed on one or more substrates (e.g., silicon die).

[0068] An exemplary operation of the oscillator circuit 400 will be described below. When a predetermined ratio is 1000 and the rate counter value is 998 output clock counts per input clock count, the delay calculator circuit 440 can calculate and set an adjustable delay to operate 2 counts slower per input clock using the adjustable delay circuit 420. As another example, an input clock signal having a frequency of 32,768 Hz and a predetermined ratio of 1,000 corresponds to an output clock signal having a frequency of 32,768,000 Hz. Thus, the total delay of the ring can be about 30.52 ns (1 / 32,768,000). If the propagation time of an individual delay circuit (e.g., an inverter circuit) is about 50 picoseconds, the oscillator circuit can include about 61 delay circuits. For example, it should be understood that an input clock signal having a frequency of 32.768 kHz can have high accuracy because it is based on a large crystal oscillator cut to an exact size. For example, crystals used in digital clocks and computer systems typically achieve an accuracy in the range of + / - 10 ppm (+ / - 0.001%) or better. Further, these input clock signals can be transmitted over relatively long distances while maintaining resistance to noise. In some variations, the input clock signal can have a frequency of 32,768 Hz, or an integer fraction of that rate (e.g., 16,384 Hz, 8,192 Hz, etc.).

[0069] In a silicon-based implementation, the oscillator circuit 400 compensates for changes in temperature, voltage, and the intrinsic speed of the silicon substrate. For example, an increase in temperature corresponds to an increase in propagation time through the delay element and a slower output clock signal. Conversely, an increase in voltage corresponds to a shorter propagation delay and a faster output clock signal. In some variations, the adjustable delay circuit 420 can have a range sufficient to compensate for variations in propagation delay within an individual silicon process. For example, a substrate (e.g., a silicon die) from one manufacturing lot can have a propagation delay that varies by up to about 20% compared to another substrate from a different manufacturing lot, even if both substrates are exposed to the same voltage and temperature. The difference in silicon between manufacturing lots is sometimes referred to as "silicon skew".

[0070] FIG. 5 is a schematic diagram of an exemplary variation of a sensor including a plurality of oscillator ring circuits. For example, sensor 500 may include a first circuit 510, a second circuit 520, a third circuit 530, and a delay calculator circuit 540. Each of the first circuit 510 and the second circuit 520 may include a plurality of delay circuits arranged in a ring configuration and a rate counter circuit similar to that illustrated and described with respect to FIG. 4. Further, the first circuit 510 may include a first adjustable delay circuit 512, and the second circuit 520 may include a second adjustable delay circuit 522. The first circuit 510 and the second circuit 520 are configured to receive an input clock signal and generate respective output clock signals having a predetermined ratio between the input clock signal and the output clock signal using the respective adjustable delay circuits 512, 522 calculated by the delay calculator circuit 540. The adjustable delay circuits 512, 522 may be configured to set a predetermined delay based on the calculated adjustable delay. That is, the adjustable delay may be calculated by comparing the ratio of the output clock signal of the first circuit 510 to the input clock signal and adjusting the adjustable delays of both the first circuit 510 and the second circuit 520 to a predetermined ratio. The delay calculator circuit 540 may be configured to calculate the difference between the output of the rate counter circuit of the first circuit 510 and a predetermined ratio. The frequencies of the first output clock signal 510 and the second output clock signal 526 are each greater than the frequency of the input clock signal.

[0071] In some variations, the first circuit 510 may include a first oscillator circuit (similar to the oscillator circuit 400). Similarly, the second circuit 520 may include a second oscillator circuit. The first circuit 510 may be configured to receive an input clock signal and output a first output clock signal 514 having a predetermined ratio between the input clock signal and the first output clock signal 514 using an adjustable delay. In some variations, the second circuit 520 may be configured to receive the input clock signal and output a second output clock signal 526 using an adjustable delay. In some variations, the third circuit 530 may be coupled to the first circuit 510 and the second circuit 520, and the third circuit 530 may be configured to generate a third signal 532 based on the difference between the first output clock signal 514 and the second output clock signal 526. The third signal 532 may correspond to a measured parameter. For example, the third signal 532 may correspond to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude. In some variations, the third signal 532 may be processed to output a parameter signal corresponding to a unit of measurement (e.g., mmHg).

[0072] In some variations, the first circuit 510 includes a first plurality of delay circuits arranged in a ring configuration. The first plurality of delay circuits may include a first plurality of inverter circuits and a first adjustable delay circuit 512. The first adjustable delay circuit 512 may include a first rate counter. The first plurality of inverter circuits may be coupled to a first multiplexer. The first plurality of inverter circuits may be configured in a closed loop with positive feedback. The first delay circuit may include a first resistor-capacitor delay circuit.

[0073] The first output clock signal 514 can vary based on a first set of parameters, and the second output clock signal 526 can vary based on a second set of parameters different from the first set of parameters. For example, the first set of parameters can include one or more of temperature and voltage. In some variations, the second set of parameters can include one or more of temperature, voltage, and force, pressure, light amplitude, sound amplitude, and resistance or capacitance corresponding to a chemical or physical reaction. That is, the second set of parameters can include the first set of parameters and at least one additional parameter.

[0074] In some variations, the third signal 532 can be processed to calculate the difference of the second output clock signal 516 with respect to an initial state (e.g., a windbag). For example, the windbag signal can be provided as a separate input or as a signal using in-band encoding on the input clock signal.

[0075] In some variations, the second circuit 520 includes a second plurality of delay circuits arranged in a ring configuration. The second plurality of delay circuits can include a second plurality of inverter circuits and a second adjustable delay circuit 522. The second adjustable delay circuit 522 can include a second rate counter. The second plurality of inverter circuits can be coupled to a second multiplexer. The second plurality of inverter circuits can be configured in a closed loop with positive feedback. The second adjustable delay circuit 522 can include one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit. The second circuit 520 can include at least one delay circuit configured to vary based on at least one additional parameter different from the first circuit 510.

[0076] In some variations, the second plurality of delay circuits may include the same delay circuits as the first set of delay circuits and at least one additional delay circuit configured to vary based on a parameter to be measured (e.g., pressure). In this way, the output clock signals 514, 526 from each of the first circuit 510 and the second circuit 520 may be different as the parameter to be measured (e.g., pressure) changes. In variations where the first circuit 510 and the second circuit 520 are disposed on the same substrate (e.g., the same silicon die), the adjustable delays due to temperature offset and voltage offset are the same for the first circuit 510 and the second circuit 520. Thus, the difference between the first output clock signal 514 and the second output clock signal 526 is due to the change in the measured parameter (e.g., pressure) and is independent of offsets such as temperature, voltage, and silicon skew. In some variations, the additional delay circuit of the second circuit 520 may include one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit. Any physical property (e.g., pressure, force, light amplitude, sound amplitude, voltage) that can cause a change in the electrical propagation time (e.g., delay) can be measured in this way. For example, the sensor 500 can be used for electrochemical analysis where a chemical reaction causes a change in resistance or capacitance. The systems, devices, and methods described reduce the complexity and size of the circuit by avoiding precision current sources and voltage measurement ADCs.

[0077] In some variations, the sensor 500 may be disposed on one or more substrates (e.g., silicon dies). For example, a single substrate may include the first circuit, the second circuit, and the third circuit. In other variations, the first substrate may include one of the first circuit and the second circuit, and the second substrate may include the other of the first circuit and the second circuit. Further, each circuit of the sensor 500 may be disposed on its own substrate or on any combination of substrates.

[0078] The exemplary operation of the oscillator circuit 500 will be described below. For an input clock signal having a frequency of 32,768 Hz and a first output clock signal having a frequency of 32,768,000 Hz, a predetermined sample rate of 200 Hz (e.g., a sample period of 5 milliseconds), a span of 1,000 mmHg pressure (from minimum to maximum value), a predetermined resolution of 0.25 mmHg, and 4,000 quantization levels are required (1,000 mmHg / 0.25 mmHg = 4,000 quantization levels). In this case, the second circuit 520 may have approximately 163,840 clocks per 5 ms sampling period. One clock period is 1 / 32,768,000 seconds (30.52 ns). Thus, the delay changes by 30.52 ns for each 0.25 mmHg of pressure. Since the 4,000 quantization levels are much less than the 163,840 clocks per 5 millisecond period, it should be understood that the count can be measured using a digital counter. If the sensor measurement requires more than 30.52 ns for each 0.25 mmHg of pressure, a faster clock rate can be used. Conversely, if the change in delay is greater than 30.52 ns for each 0.25 mmHg of pressure, a slower clock can be used.

[0079] In some variations, an optional fourth circuit (e.g., the fourth circuit 310 of FIG. 3) may be configured to measure different parameters than the second circuit 520. For example, the fourth circuit may include a delay circuit configured to vary based on temperature. The fourth circuit may have a configuration similar to the second circuit 520 described herein.

[0080] In some variations, the fourth circuit may be coupled to the third circuit. The fourth circuit may be configured to receive an input clock signal and output a fourth output clock signal using an adjustable delay. The third circuit may be configured to generate a fifth signal based on the difference between the first output clock signal and the fourth output clock signal. The fifth signal corresponds to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude. In this way, the sensor 500 may be configured to measure multiple parameters while compensating for offsets without using an offset compensation circuit.

[0081] In some variations, the sensor 500 may be powered by a set of three wires including a first wire associated with a positive voltage, a second wire associated with ground, and a third wire associated with an input clock signal (which may be referenced to ground). In some variations, the power may be derived from only the input clock signal.

[0082] In some variations, the sensor described herein may be disposed in a 50 nm process including about 5,000 gates and about 10,000 gates / mm 2 and may have a size greater than about 0.3 mm. In some variations, the sensor 500 may include a low-pass filter to reduce noise on the power supplied to the delay element (e.g., noise above 16.384 kHz corresponding to the Nyquist rate of a 32.768 kHz crystal). 2

[0083] Figures 9A and 9B show schematic diagrams of two different ring oscillator circuits that can be used in combination to provide respective count values, and the count values from the two different ring oscillator circuits can be used to determine the value of a parameter of interest (e.g., pressure, force, optical amplitude, audio amplitude, radiation, resistance or capacitance corresponding to a chemical or physical reaction, etc.). FIG. 9A shows a schematic diagram of an oscillator circuit 900A comprising a set of delay circuits 910A and parameter-based delay circuits 920 arranged in a ring configuration (i.e., a first ring circuit), a rate counter circuit 930A (i.e., a counter), and a latch circuit 950A (i.e., a latch). The delay of the parameter-based delay circuit 920 varies based on the parameter of interest (e.g., the delay increases as the pressure decreases and the delay decreases as the pressure increases, etc.). FIG. 9B shows a schematic diagram of an oscillator circuit 900B comprising a set of delay circuits 910A arranged in a ring configuration (i.e., a second ring circuit), a rate counter circuit 930B, and a latch circuit 950B. The oscillation rate of the second ring circuit varies based on a first set of parameters (e.g., temperature and voltage) that do not include the parameter of interest, while the oscillation rate of the first ring circuit varies based on the first set of parameters and the parameter of interest. The oscillator circuit 900A can function similarly to a measurement circuit for determining a provisional predicted value of the parameter of interest, and the oscillator circuit 900B can function similarly to a calibration circuit for adjusting the provisional predicted value by compensating for changes potentially caused by the first set of parameters.

[0084] Referring to FIG. 9A, the oscillation rate of the first ring circuit can be sampled at a first sample rate (i.e., a predetermined sample rate), and the rate counter circuit 930A and the latch circuit 950A can be used to count and store the oscillation frequency of the first ring circuit during each sample period (e.g., at each rising edge of the sample rate clock), respectively. For example, if the first ring circuit is oscillating at 100 MHz and the sample rate is 256 Hz (approximately 1 sample every 4 ms), the rate counter circuit 930A counts approximately 400,000 oscillations of the first ring circuit every 4 ms. For each sample period, the latch circuit 950A receives the output count signal and can store a representation of the count value counted by the rate counter circuit 930A during that sample period for future processing (as indicated in the output count signal). As mentioned above, the oscillation frequency in the first ring circuit can vary over the sample period based on a first set of parameters and at least one additional parameter (i.e., the parameter of interest). Thus, the output of the latch circuit 950A can be a nearly continuous characterization of the behavior of the first ring circuit with respect to the first set of parameters and the parameter of interest. In some variations, the delay circuit 910A can include a set of inverters. In some variations, the set of inverters can be coupled to a multiplexer. In some variations, the set of inverters is configured within a closed loop with positive feedback. In some variations, the first ring circuit can include one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit.

[0085] Referring to FIG. 9B, the oscillation rate of the second ring circuit can be sampled at a second sample rate (i.e., a predetermined sample rate), and the rate counter circuit 930B and the latch circuit 950B can be used to count and store the oscillation frequency of the second ring circuit during each sample period, respectively. As mentioned above, since the oscillation frequency in the second ring circuit does not include a parameter-based delay circuit, it can change based on a first set of parameters over the sample period, but does not change based on the parameter of interest. Therefore, the output of the latch circuit 950B can be an almost continuous characterization of the behavior of the second ring circuit with respect to the first set of parameters. In some variations, the second ring circuit oscillates at a rate of 30 to 60 MHz (e.g., + / - 20% per die, + / - 20% based on voltage and temperature, etc.). In some variations, since the temperature generally changes relatively slowly with respect to the sample rate, for example, when the first set of parameters includes temperature, multiple sample periods can be averaged (e.g., total count of oscillations over the range of sample periods / number of sample periods within the range of sample periods). In some variations, the delay circuit 910B can include a set of inverters. In some variations, the set of inverters can be coupled to a multiplexer. In some variations, the set of inverters is configured within a closed loop with positive feedback. In some variations, the second ring circuit can include one or more of a resistor-capacitor delay circuit, a resistor-inductor delay circuit, and a capacitive delay circuit.

[0086] FIG. 10 shows a schematic diagram of a sensor 1000 that includes two ring oscillator circuits (e.g., oscillator circuits 900A and 900B) that utilize a comparison of counts to determine a parameter of interest. The output of sensor 1000 can be a digital signal, and an ADC need not be included in sensor 1000 (this can save space and / or reduce size). In some variations, sensor 1000 can be a single chip. Sensor 1000 can include a first ring circuit (i.e., Ring #1 in FIG. 10) (similar to the first ring circuit described with respect to FIG. 9A) that oscillates at a first rate (e.g., 100 MHz), and a second ring circuit (i.e., Ring #2 in FIG. 10) (similar to the second ring circuit described with respect to FIG. 9B) that oscillates at a second rate (e.g., 32 MHz). The second rate can vary in response to a first set of parameters (e.g., temperature and voltage), but may not vary in response to a parameter of interest (e.g., pressure), and the first rate can vary in response to the first set of parameters and the parameter of interest. Similarly, the second rate can vary in response to a set of parameters, and the first rate can vary in response to a different set of parameters. As mentioned above, Ring #1 and Ring #2 can be on the same die. Thus, at least some physical parameters of both rings (e.g., the first set of parameters) will have substantially (e.g., within 1%, within 2%, within 5%, within 10%, within 25%) the same variation (e.g., the same silicon process variation, the same voltage variation, the same temperature variation, etc.). In some variations, Ring #1 and #2 can be on different dice.

[0087] Still referring to FIG. 10, an input clock signal (e.g., 32,768 Hz input clock, i.e., the input clock) is input to the frequency division circuit 1010, and the frequency division circuit 1010 can output a signal having a predetermined sample rate (e.g., 200 Hz, 256 Hz, etc.). The signal having the predetermined sample rate can then be input to the first rate counter circuit 1030A, the first latch circuit 1050A, the second rate counter circuit 1030B, and the second latch circuit 1050B. For each sample period, the first rate counter circuit 1030A can count the oscillation frequency in ring #1 during that sample period, and the second rate counter circuit 1030B can count the oscillation frequency in ring #2 during that sample period. The first latch circuit 1050A can store the first count value from the first rate counter circuit 1030A for each sample period, and the second latch circuit 1050B can store the second count value from the second rate counter circuit 1030B for each sample period. For each sample period, the parameter calculator circuit 1070 of interest (e.g., the third circuit) can (1) receive the first count value from the first latch circuit 1050A (counted by the first rate counter circuit 1030A) during that sample period, and (2) receive the second count value from the second latch circuit 1050B (counted by the second rate counter circuit 1030B) during that sample period. Then, the parameter calculator circuit 1070 of interest can use both the first and second count values to determine the value of the parameter of interest (e.g., the pressure value) (e.g., represented as the third signal). In some variations, the parameter calculator circuit 1070 of interest can use one or more look-up tables to determine the value of the parameter of interest. In some variations, the parameter calculator circuit 1070 of interest can use an equation that is a function of both the first and second count values to determine the value of the parameter of interest. In some variations, the function of the parameter calculator circuit 1070 of interest can be executed on a separate chip as shown in FIG. 11A or FIG. 11B.In some variations, the first count value may be modified based on the second count value to determine the value of the parameter of interest.

[0088] FIG. 10 shows two ring oscillator circuits (i.e., Ring #1 and Ring #2), but in some variations, three or more ring oscillator circuits may be used. In some variations, one or more additions (e.g., a third ring oscillator circuit, a fourth ring oscillator circuit, etc.) may be added to the sensor 1000 shown in FIG. 10. For example, in some variations, a plurality (e.g., two, three, four, or more) of ring oscillator circuits similar to Ring #1 may be used in a manner similar to that described above with respect to FIG. 10 to enable the determination of the value of another parameter of interest. FIG. 10 shows a first rate counter circuit 1030A, a first latch circuit 1050A, a second rate counter circuit 1030B, and a second latch circuit 1050B, but in some variations, any number (e.g., one, three, six, eight, etc.) of rate counter circuits and / or latch circuits may be used. For example, in some variations, the sensor 1000 may further include a third ring oscillator circuit that includes a parameter-based delay element that changes the delay at a rate different from other elements within, for example, the first, second, and / or third ring oscillator circuits. The difference in count values between the additional (e.g., third, fourth, etc.) ring oscillator circuit and the first and / or second ring oscillator circuits may be used to determine the value of another parameter of interest (e.g., force, optical amplitude, acoustic amplitude, radiation, resistance or capacitance corresponding to a chemical or physical reaction, etc.). In some variations, the difference in count values between the additional (e.g., third) ring oscillator circuit and the first and / or second ring oscillator circuits may be used to measure or otherwise determine the die temperature.

[0089] In some variations, the temperature of the first or second ring oscillator may be determined using pulse time delay measurements. For example, the time of the pulse or a known voltage may be measured, and if the voltage is tightly controlled, an assumption may be made that the time is different from other pulses based only on temperature.

[0090] The various circuits contemplated herein may be included on any number of chips, dies, and / or substrates. In some variations, the various circuits contemplated herein may be included across multiple chips, dies, and / or substrates. FIG. 11A shows a schematic of a sensor 1100A that includes a sensor chip 1120A and a computing device, which in this example is a microcontroller chip 1130A. The output of sensor 1100A may be a digital signal, and an ADC need not be included in sensor 1100 (this can save space and / or reduce size). The circuitry of sensor chip 1120A may be similar to that of sensor 1000 of FIG. 10, but may include a serializer circuit 1110A instead of the parameter calculator circuit 1070 of interest from FIG. 10 (which can reduce the size of sensor chip 1120A). For each sample, serializer circuit 1110A may receive the first count value of ring #1 from a first latch circuit, receive the second count value of ring #2 from a second latch circuit, and provide a serialized representation of both count values to output circuit 1140A. Serializer circuit 1110A may be electrically coupled to output circuit 1140A via a wire (e.g., at least 10 cm long, at least 20 cm long, at least 30 cm long, at least 40 cm long, at least 50 cm long, at least 100 cm long, about 50 - 100 cm). In some variations, output circuit 1140A is a universal asynchronous receiver / transmitter (UART). The output from output circuit 1140A may be provided to a parameter calculator circuit 1170A of interest, which may use the output signal from serializer circuit 1110A to determine the value of the parameter of interest. In some variations, sensor chip 1120A may include inputs / outputs (I / O) for power, ground, and clock. In some variations, power may be extracted from the clock to power sensor chip 1120A. In some variations, the sample rate may be 256 Hz, and serializer 1110A may output any suitable number of bits per sample period, such as 38 bits or 40 bits per sample period, for example.In some variations, ring #1 may include one or more inverters (e.g., two, three, or more), and a resistor capacitor (RC) circuit, and the piezoresistive element varies the resistor within the RC circuit. The piezoresistive element may have a resistance of 1999.88 to 2000.12 ohms / mmHg and a 5 pF capacitor, and the delay results in a first rate that is 90 to 100 MHz. In some variations, a moving average of the count values from ring #2 (e.g., a 1-second moving average) may be used by the parameter calculator circuit 1170A of interest (e.g., instead of the count value from a single sample period). In some variations, the sensor chip 1120A may communicate wirelessly with the microcontroller chip 1130A. In some variations, the sensor chip 1120A may communicate with the microcontroller chip 1130A via a wired connection (and not wirelessly). In some variations, the sensor includes a first circuit (e.g., oscillator circuit 900A) configured to receive an input clock signal and output a first output count signal at a predetermined sample rate (e.g., 200 Hz, 250 Hz, etc.). The sensor may further include a second circuit (e.g., oscillator circuit 900B) configured to receive the input clock signal and output a second count signal at the predetermined sample rate. The sensor may further include a third circuit (e.g., parameter calculator circuit 1070, sensor chip 1120A, microcontroller chip 1130A, output circuit 1140A, parameter calculator 1170A of interest) coupled to the first and second circuits. The third circuit may be configured to generate a third signal (e.g., representing the value of the parameter of interest) based on the first output count signal and the second output count signal.

[0091] Figures 11A and 11B show exemplary circuit diagrams for measuring parameters using two oscillator rings. As shown in Figures 11A and 11B, ring #1 is set to oscillate at a relatively high frequency, for example, within the range of about 50 MHz to about 100 MHz. The rate at which ring #1 oscillates can be affected by several factors such as, for example, the temperature of the die, the supplied voltage, and the intrinsic speed of the silicon, and these factors can vary by + / - 20% between different silicon dies from different wafers.

[0092] The sensor delay can vary according to the attribute being measured. In an example configuration where the sensor delay varies in response to pressure, the pressure can also affect the rate of oscillation of ring #1 by including a piezoresistive pressure sensing unit within the die. Thereby, a change in pressure directly results in a change in the oscillation rate of only ring #1. Note that oscillator ring #2 is configured to have no change with respect to a change in pressure (since there is no sensor delay component).

[0093] An accurate low-speed input clock such as 32.768 kHz can be divided to generate a sampling rate such as 200 Hz (as shown in FIG. 11A for example) or 256 Hz (as shown in FIG. 11B for example). The oscillation of the ring can increment a counter, and at the sampling rate, the count value can be latched and the counter can be reset to 0. Thus, at the end of each sample period, the latch can contain the number of oscillations of the ring during the last sample period. For example, for a 256 Hz sample rate, the ring can oscillate hundreds of thousands of times. To measure blood pressure in the range of -50 mmHg to +300 mmHg, only 1400 quantization levels may be required (e.g., may be required) to achieve a resolution of 0.25 mmHg. The 1400 quantization levels are only a small part of the 400,000 clocks typically counted during the sample period, and the resolution of the sensor only needs to result in a change of a few counts of the counter. Note that at an oscillation rate of 100 MHz, 1 count is only 10 nanoseconds. Thus, a 1 mmHg pressure change only needs to result in a change in delay time of 50 to 100 nanoseconds.

[0094] The ring #2 in FIGS. 11A and 11B can be configured to be latched at the same rate as ring #1, but since ring #2 does not have a piezoresistive element (i.e., sensor delay) as part of its structure, the oscillation rate of ring #2 can be insensitive or indifferent to changes in pressure. Thus, the oscillation rate of ring #2 can be affected only by, for example, temperature, voltage, and the intrinsic properties of silicon. As the temperature of the die increases, the oscillation rate slows down, and as the temperature decreases, the oscillation rate speeds up. Similarly, as the voltage increases, the oscillation rate increases, and as the voltage decreases, the oscillation rate decreases. Since ring #2 is on the same silicon die as ring #1, the temperature and voltage can be the same, and the changes due to temperature and voltage can be the same as those of ring #1. Then, the change in the latched value of ring #2 can be used when calculating the sensed characteristics measured by ring #1. Thus, ring #2 can operate like a continuous calibration of the sensor die where recalibration is performed at the sample rate.

[0095] In a variation where the sensors described herein are utilized to measure pressure in a clinical setting, a system or medical device equipped with a pressure sensor can be "pumped down" (zeroed) prior to insertion into the body. The system or device can then be configured to determine and / or store the clock rates of both rings. When the sensor is placed inside the body, the temperature can increase and ring #2 can operate slower. The amount by which ring #2 operates slower can be incorporated into the calculations for converting the rate of ring #1 into pressure.

[0096] Any clock can be used for the low-speed input clock, but in some variations, a 32.768 kHz clock may be desirable. For example, in variations where accuracy is particularly desirable, since the sensors described herein can utilize a clock derived from a crystal. These crystals always achieve an accuracy of + / - 5 ppm (0.0005%), and thus the use of these crystals will only add a small error (which is likely to be essentially insignificant (estimated to be within the range of 0.5 mmHg in the case of a pressure sensor)).

[0097] When two counter values are latched, a small area on the die can be used to send these values as a digital output (e.g., a digital communication packet). In some variations, the values can be sent as a serial packet that can be directly read by a computing device (e.g., microcontroller 1130A or 1130B). In some variations, a Universal Asynchronous Receiver Transmitter (UART) protocol h can be utilized. The UART protocol supports communication packets that can be of a length of about 1 byte and up to about several thousand bytes. As an example, in a variation where each counter is 19 bits, only 38 bits need to be sent, which can fit within a simple 5-byte (40-bit) packet. Although the UART is discussed herein and can be utilized in some variations, in other variations, other communication protocols can be used instead of or in addition to the UART.

[0098] At least some of the variations described herein can use two or more rings and can use a computing device to perform runtime calibration.

[0099] The above examples involve pressure measurements, but the same general techniques can measure other physical properties such as force, light amplitude, acoustics, or an electrochemical reaction. The sensor delay can result in a measurable change in impedance, capacitance, or inductance. Otherwise, the sensor delay can result in a change in the propagation speed of an electrical signal within the ring.

[0100] One advantage of this sensor configuration is that the die is not limited to two rings. For example, in some variations, the sensors described herein may include a third ring with an oscillation rate that can be modified by different physical properties. For example, the third ring can be set to have additional sensitivity to temperature (relative to Ring #2), and thus can provide a very accurate report of the patient's core body temperature. A fourth ring can be employed with an oscillation rate that can vary based on electrochemical properties such as pH. At a higher sample rate, it may be possible to pick up the acoustic signature associated with the opening and closing of the heart valves. In each of these variations, the analog signal can be converted to digital data that can be sent via a single wire using a digital message. Additional sensing may simply require a slightly larger message. For example, at a sample rate of 256 Hz and an input clock of 32.768 kHz, a single output wire can send 128 bits during each sample period. This can accommodate five different sensors each having a 19-bit resolution. If a higher resolution or a higher sample rate is desired, the clock rate can be doubled or one or more additional wires can be added. The ability to transition from analog signal transmission to digital signal transmission has a significant impact on signal fidelity, interoperability with existing patient monitoring devices, and miniaturization of SSPT devices, and can be applied across many aspects of patient care, particularly in prolonged field care (PFC) where size and power requirements are of utmost importance.

[0101] As can be seen from the figures, FIG. 11B shows sensor chip 1120B and microcontroller chip 1130B. Sensor 1110B is substantially the same as sensor 1110A in FIG. 11A, but has a different sample rate. Sensor 1100B uses a sample rate of 256 Hz, and sensor 1100A uses a sample rate of 200 Hz. FIG. 11A shows serializer 1110A as separate from the two latches, but the latch serializer 1110B from FIG. 11B can be a combination of the two latches and the serializer 1110A from FIG. 11A. Of course, the sample rates of 200 Hz and 256 Hz are examples, and some variations can use different sample rates.

[0102] In some variations, the start and stop bits can be latched directly to the shift resistor. For example, FIG. 13A shows an example of a latch serializer communicatively coupled to two 19-bit counters, such as the latch serializer 1110B of FIG. 11B, similar to the serializer 1110A, and two latches coupled to the serializer 1110A of FIG. 11A. In the example shown in FIG. 13A, a 32.768 kHz input clock is divided into a 256 Hz latch signal and a 16384 Hz shift signal. A 47-bit latch shift resistor receives values from each of a shift-in signal, a latch signal, and a shift signal, as well as two 19-bit counters, a start bit, and a stop bit. In this variation, the 47-bit latch shift resistor outputs a UART-type serial output. Based on the 256 Hz latch signal, the counter values and the UART start bit (“0”) and stop bit (“1”) are latched directly to the 47-bit output shift resistor in the correct order. The shift resistor “shifts” based on the 16,384 Hz clock. This results in 64 bits during each 1 / 256 Hz sample period (16,384 bits / 256 = 64). After the first 47 bits are sent out, a “1” is shifted in, so the next 17 bits sent are all 1s. These “1s” properly complete byte 5 (including its stop bit) and result in 14 idle (“1”) bits before the next frame. The UART-type serial output is shown in FIG. 13B. Each frame has a specific number of bytes within the range where there is no delay between bytes. During the idle time between frames, in some variations, the digital output can be high (represented by 1). In some variations, each data byte is preceded by a single start bit (e.g., low) and a single stop bit (e.g., high). In some variations, the individual data bits within a byte are sent with the most significant bit first. In one example, the 5 bytes within a frame can be: (1) Byte 1: bit 7 = ring #1 count bit 18.Bit 6 = Ring #1 Count Bit 17, ..., Bit 0 = Ring #1 Count Bit 11, (2) Byte 2: Bit 7 = Ring #1 Count Bit 10, Bit 6 = Ring #1 Count Bit 9, ..., Bit 0 = Ring #1 Count Bit 3, (3) Byte 3: Bit 7 = Ring #1 Count Bit 2, Bit 6 = Ring #1 Count Bit 1, Bit 5 = Ring #1 Count Bit 0, Bit 4 = Ring #2 Count Bit 18, Bit 3 = Ring #2 Count Bit 17, ..., Bit 0 = Ring #2 Count Bit 14, (4) Byte 4: Bit 7 = Ring #2 Count Bit 13, Bit 6 = Ring #2 Count Bit 12, ..., Bit 0 = Ring #2 Count Bit 6, (5) Byte 5: Bit 7 = Ring #2 Count Bit 5, Bit 6 = Ring #2 Count Bit 4, ..., Bit 2 = Ring #2 Count Bit 0, Bit 1 = Always 1, Bit 0 = Always 1. One advantage of the variant shown in FIGS. 13 and 13B is that a state machine (e.g., for tracking byte or packet boundaries) is not required.

[0103] In one example, the serial output can be at a rate that is half of the input clock. In one example, a single flip-flop can be used to generate a 16,384 kHz clock, and a 6 flip-flop divider of that 16,384 kHz clock is used to obtain a 256 Hz sample rate. At each sample boundary, the values from two counters can be latched. In some variants, rather than constructing a state machine to process start / stop bits, 38 counter bits (2×19) and the start / stop bits can be directly latched into a single 47-bit shift resistor. In one example, since there are 10 bits per byte, a 47-bit (not 50-bit) shift resistor is sufficient, but the last 3 bits of byte 5 are always 1. At the output clock rate (16,384 kHz), bits from the shift resistor are shifted out and a '1' is shifted in at the other end. This results in outputting a '1' during the time between 5 bytes.

[0104] b. Output Device Generally, the output devices described herein can be configured to output a signal corresponding to the measured parameters described herein. For example, the output signal can be a digital signal such that a circuit such as an ADC is not required, thus reducing the complexity of the device. In some variations, the controller 320 can include an output device 328 configured to output the third signal 532 as a digital signal. For example, the output device 328 can be configured to output the third signal 532 as a set of binary-encoded bits at a periodic rate. In some variations, the output device 328 can include one or more of a wire configured for wired transmission and an antenna configured for wireless transmission. In some variations, the third signal 532 can be encoded and / or output on a separate wire to increase noise immunity.

[0105] As described herein, the measured parameters can be represented by 4,096 quantization levels that can be transmitted as a digital signal using 12 bits at a predetermined rate (e.g., once every 5 milliseconds, 3,200 bits per second). It should be understood that a transmission rate of less than 5,000 bits per second has high noise reliability because each bit is long enough such that a noise burst is shorter than an individual bit time.

[0106] In some variations, the digital signal includes one or more of standard binary encoding (e.g., UART), pulse width modulation (PWM), and Manchester encoding. In some variations, the output device may include a universal asynchronous receiver / transmitter (UART). Thus, the output device may not have a PGA and / or ADC, and thus reduces component count and manufacturing complexity. In some variations, the digital signal may be output using one or more of a wire and an antenna. There are several ways to provide a binary-encoded value on a single wire, including standard NRZ or NRZI UART techniques having a start bit, 8 encoded bits, and a stop bit. In some variations, the digital signal may be output as multi-byte ASCII text and / or grayscale encoding.

[0107] In some variations, the output device may include a serializer (e.g., serializer circuit 1120), which may include a circuit configured to convert parallel data to serial data and / or vice versa. In some variations, the output device may include an output resistor, which may include a flip-flop and a circuit configured to store data.

[0108] c. Processor As depicted in FIG. 3, the sensor system 300 may include a processor 322 and a machine-readable memory 324 (e.g., collectively a controller) that communicates with one or more computing devices 340. The processor 322 may be connected to the computing device 340 via a wired or wireless communication channel. The processor 322 may be configured to control one or more components of the sensor system 300, such as the communication device 330. The processor 322 may be implemented to suit a wide variety of general-purpose or special-purpose computing systems or configurations. Various exemplary computing systems, environments, and / or configurations suitable for use with the systems and devices disclosed herein may include, but are not limited to, software or other components implemented within or on personal computing devices, network devices, servers or server computing devices such as routing / interconnecting components, portable (e.g., laptop) or notebook devices, multiprocessor systems, microprocessor-based systems, and distributed processing networks.

[0109] Processor 322 may incorporate data received from memory 324 and computing device 340 to control system 300. Memory 324 may further store instructions that cause processor 322 to execute modules, processes, and / or functions associated with system 300 and / or computing device 340. Processor 322 can be any suitable processing device configured to operate on and / or execute a set of instructions or code, and may include one or more microcontrollers, data processors, image processors, image processing units, physical processing units, digital signal processors, and / or central processing units. Processor 322 can be, for example, a general-purpose processor, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and can be configured to execute application processes and / or other modules, processes, and / or functions associated with the system and / or a network associated therewith. For example, processor 322 can be a dual-core microcontroller. The underlying device technology can be provided in various component types, such as metal-oxide semiconductor field-effect transistor (MOSFET) technology like complementary metal-oxide semiconductor (CMOS), bipolar technology, polymer technology (e.g., silicon conjugated polymers, and metal-conjugated polymer-metal structures), analog and digital, and combinations thereof, etc.

[0110] d. Memory Some variations of the memory 324 described herein relate to computer storage products having a non-transitory computer-readable medium (which may also be referred to as a non-transitory processor-readable medium) having instructions or computer code for performing various computer-implemented operations. The computer-readable medium (or processor-readable medium) is non-transitory in that it does not include a transitory propagated signal (e.g., a propagated electromagnetic wave that conveys information on a transmission medium such as air or cable) itself. The medium and the computer code (also referred to as code or algorithm) can be designed and constructed for a specific purpose or purposes. Examples of non-transitory computer-readable media include, but are not limited to, flash memory, non-volatile memory (e.g., Intel® Optane™, 3D XPoint™), magnetic storage media such as hard disks, floppy disks, and magnetic tape; optical storage media such as compact discs / digital video discs (CD / DVD), compact disc-read only memory (CD-ROM), and holographic devices; magneto-optical storage media such as optical discs; solid state storage devices such as solid state drives (SSD) and solid state hybrid drives (SSHD); carrier signal processing modules; and hardware devices specifically configured to store and execute program code, such as application specific integrated circuits (ASIC), programmable logic devices (PLD), read-only memory (ROM), and random-access memory (RAM) devices. Other variations described herein relate to computer program products, which may include, for example, the instructions and / or computer code disclosed herein.

[0111] The systems, devices, and / or methods described herein may be implemented by software (executed on hardware), hardware, or a combination thereof. Software modules (executed on hardware) may be expressed in various software languages (e.g., computer code), including C, C++, Java®, Python, Ruby, Visual Basic®, and / or other object-oriented, procedural, or other programming languages or development tools. Examples of computer code include, but are not limited to, microcode or microinstructions, machine instructions such as those generated by a compiler, code used to generate web services, and files containing high-level instructions that are executed by a computer using an interpreter. Additional examples of computer code include, but are not limited to, control signals, encryption code, and compression code.

[0112] e. Communication device In some variations, the sensor system 300 described herein may communicate with one or more of a blood control device, a network, and a computer system through the communication device 330. In some variations, the sensor system 300 may communicate with other devices (e.g., computing devices) via one or more wired and / or wireless networks. A wireless network may refer to any digital network that is not connected by any kind of cable. Examples of wireless communication of a wireless network include, but are not limited to, Bluetooth, cellular phones, radio, satellite, and microwave communication. However, a wireless network may be connected to a wired network to interface with the Internet, other carrier voice and data networks, business networks, and personal networks. A wired network is typically carried via copper twisted pair, coaxial cable, and / or fiber optic cable. There are many different types of wired networks, including wide area network (WAN), metropolitan area network (MAN), local area network (LAN), Internet area network (IAN), campus area network (CAN), global area network (GAN) similar to the Internet, and virtual private network (VPN). Hereinafter, a network generally refers to any combination of wireless, wired, public, and private data networks interconnected via the Internet, providing an integrated networking and information access system. In some variations, any of the data stored in the memory 324 may be transmitted using the communication device 330.

[0113] Mobile communications may include technologies such as GSM, PCS, CDMA or GPRS, W-CDMA, EDGE or CDMA2000, LTE, WiMAX, and 5G networking standards. In the deployment of some wireless networks, networks are combined from multiple mobile wireless networks or a mixture of mobile wireless, Wi-Fi, and satellite communications is used. In some variations, the network interface may comprise a radio frequency receiver, transmitter, and / or an optical (e.g., infrared) receiver and transmitter. The communication device 330 may communicate with one or more components of the system 300 both wired and / or wirelessly.

[0114] II. Sensor housing The sensors described herein can be integrated into various devices, such as an elongated body (e.g., a catheter) used in a blood flow control device and a pressure monitoring device, which are housed, positioned, and / or encapsulated within a sensor housing as further described below. The sensors can monitor physiological states during medical procedures and / or monitor a patient's physiological functions during routine and critical medical procedures. In some variations, the sensor housing can be a tubular member that includes an opening (e.g., a window) configured to expose the sensor to the surrounding environment (e.g., blood within a blood vessel) and / or one or more struts to assist in attaching the sensor housing (and thus the sensor) to the elongated body. In some variations, the sensor housing can be coupled or otherwise affixed to a sleeve. The sleeve can be positioned around or otherwise surround the elongated body, thereby coupling the sensor to the elongated body. Depending on the number of sensors included within the elongated body, one or more sensor housings can be integrated within the elongated body. In another variation, the sensor and / or sensor housing can be configured to be sized smaller (e.g., having a small diameter) so that the sensor can be integrated into an elongated body (e.g., a catheter) for advancement into a blood vessel or for advancement through an arterial or venous catheter (e.g., an arterial or venous access line). The sensor housing can be configured to protect the sensor from damage due to moisture or fluid ingress (e.g., exposure to blood) and / or from the effects of pressure (e.g., pressure from a balloon of a blood flow control device).

[0115] The sensor housing can be formed from any suitable biocompatible material. For example, in some variations, the sensor housing can be formed from polymers such as, for example, polytetrafluoroethylene (PTFE), polyimide, Pebax®, thermoplastic polymers, and combinations thereof. Exemplary thermoplastic polymers can be, for example, polycarbonate, polycarbonate / acrylonitrile-butadiene-styrene terpolymer blend, and the like. In some variations, the sensor housing can be formed from metals such as, for example, stainless steel, bondable metal alloys, or combinations thereof. In one variation, the sensor housing includes stainless steel. In variations where each of the sleeve and the sensor housing comprises a metal (e.g., stainless steel) tube, the tubes can be laser welded together, and the openings can be cut through the tubular walls of both the sleeve and the sensor housing to expose the sensor or otherwise provide access to the sensor.

[0116] In some variations, as mentioned above, the sensor can be fully or partially encapsulated within the sensor housing. The sensor can be encapsulated, for example, using various polymers. Encapsulating the sensor within the housing can make the sensor readings less susceptible to bending forces acting on the sensor and / or can help isolate the sensor from the effects of pressurization when a pressurizing device is employed, for example, to measure, monitor, and / or adjust blood pressure. Encapsulating the sensor entirely or partially within a polymer can also function as a sealant to protect the electrical components of the sensor from moisture or fluid ingress. Thus, encapsulation within the polymer can make the sensor readings more consistent. In some variations, the sensor can be fully or partially encapsulated within RTV (room temperature vulcanizing) silicone within a metal (e.g., stainless steel) housing.

[0117] Exemplary polymers for use in encapsulating the sensor, in whole or in part, include, but are not limited to, hydrophobic polymers such as RTV silicone, polytetrafluoroethylene (PTFE), polyimide, and Pebax®, and combinations thereof. In one variation, the step of encapsulating the sensor can include forming a layer of polymer, such as an RTV silicone or a layer containing different polymers, within the sensor housing, placing the sensor on the polymer layer, and then curing the polymer. Next, the sensor can be encapsulated by covering the sensor with additional polymer, such as RTV silicone, and then curing the polymer. The polymer can have compliance that allows for the transmission of a pressure signal through the polymer such that physiological conditions, such as pressure, can be transmitted to the sensor through the polymer. In some variations, a separate seal (e.g., an epoxy seal) can be disposed within the sensor housing to protect the sensor from the effects of pressurization. Instead of encapsulating the sensor, the polymers described herein can be used to coat the sensor and any associated components (e.g., wires, wire pads). In variations where the sensor is not encapsulated, the aforementioned polymers can be used to adhere the sensor to the sensor housing, or an adhesive can be used to secure the sensor to the sensor housing.

[0118] The sensor housing can have any suitable size, shape, and geometry. For example, the sensor housing can have a tubular, rectangular, square, or oval shape. In one variation, the sensor housing can be of a tubular shape and can include an opening (e.g., a window) as mentioned above. The dimensions of the sensor housing can be such that the sensor fits snugly within the sensor housing, thereby minimizing the use of space on the elongated body.

[0119] A. Tubular Sensor Housing As mentioned above, in some variations, the sensor housing may have a tubular shape. In these variations, the inner diameter of the sensor housing can be from about 0.01 inch to about 0.04 inch (including all values and sub - ranges therein). In some variations, the inner diameter of the sensor housing can be, for example, from about 0.012 inch (0.30 mm) to about 0.035 inch (0.89 mm), from about 0.015 inch (0.38 mm) to about 0.03 inch (0.76 mm), from about 0.017 inch (0.43 mm) to about 0.025 inch (0.64 mm), or from about 0.019 inch (0.48 mm) to about 0.022 inch (0.56 mm) (including all values and sub - ranges therein). In one variation, the inner diameter of the sensor housing can be about 0.02 inch (0.51 mm). In some variations, the outer diameter of the sensor housing can be from about 0.02 inch (0.51 mm) to about 0.08 inch (2.0 mm) (including all values and sub - ranges therein). In some variations, the outer diameter of the sensor housing can be, for example, from about 0.021 inch (0.53 mm) to about 0.06 inch (1.5 mm), from about 0.022 inch (0.56 mm) to about 0.04 inch (1.0 mm), from about 0.023 inch (0.58 mm) to about 0.03 inch (0.76 mm), from about 0.024 inch (0.61 mm) to about 0.027 inch (0.69 mm) (including all values and sub - ranges therein). In one variation, the outer diameter of the sensor housing can be about 0.025 inch (0.64 mm).

[0120] Figures 17A - 17C show an exemplary tubular sensor housing. Referring to Figures 17A - 17C, sensor 1700 can be disposed within tubular sensor housing 1702. Sensor 1700 can include MEMS piezoresistive sensor 1700a on CMOS bare die 1700b. Window 1704 formed through the wall of tubular sensor housing 1702 can expose sensor 1700 to the external environment (e.g., blood flowing through an artery or vein). As shown in the cross - sectional view of Figure 17C, sensor 1700 can be sized such that sensor 1700a and die 1700b fit tightly within lumen 1706 of tubular sensor housing 1702. An adhesive, e.g., RTV adhesive, can be included within tubular sensor housing 1702 (e.g., under sensor 1700) to fixedly attach sensor 1700 thereto. In some variations, the adhesive can also be included to partially or fully encapsulate sensor 1700 within tubular sensor housing 1702. Wire bond pads 1708 for connecting CMOS circuit 1710 on sensor 1700 are supplied through window 1704 and can then be coated (or encapsulated) with an adhesive (e.g., the adhesive used to encapsulate or attach sensor 1700 to tubular housing 1702).

[0121] Sensors housed within a tubular sensor housing (e.g., the housing of Figures 17A - 17C) can have any width and thickness that allows them to be incorporated within the sensor housing and / or an elongate body, and can vary depending on the parameter being measured and / or the device in which it is included (e.g., a blood flow control device, a pressure measurement device, or other medical or non - medical device that measures one or more of temperature, voltage, force, pressure, light amplitude, and sound amplitude). In some variations, the sensor can be configured to have any width, thickness, and height as previously described herein. In other variations, the sensor width can be about 330 microns and the sensor thickness can be about 250 microns.

[0122] B. Sensor Housing with Struts Some variations of the sensor housing may include one or more structural components configured to couple the sensor housing to an elongated body (e.g., a catheter). The structural components may be configured as struts having edges that may be useful when attaching (e.g., welding) the sensor housing to the elongated body. For example, a window of the sensor housing may be aligned with an opening of the elongated body, and the struts may be attached to the elongated body at one or more of the strut edges. The height of the struts may be such that the sensor housing is properly positioned within the lumen of the elongated body and interference with external elements that may affect the functionality of the sensor is minimized. For example, the sensor may be exposed just enough to obtain accurate sensor measurements, but protected from damage by being disposed within the sensor housing.

[0123] For example, as shown in FIG. 18, the sensor housing 1800 may include a body portion 1806, a window 1808, a notch 1804, and two struts 1802 that may be used to couple the sensor housing 1800 to an elongated body (not shown). The struts 1802 and the notches 1804 on the outside of the struts 1802 may be useful for attaching (e.g., laser welding) the sensor housing 1800 to the elongated body. The sensor housing 1800 may have a diameter sized to fit within the elongated body and, in some variations, may have a diameter of about 0.1 Fr to about 5 Fr (including all values and subranges therein). For example, the sensor housing may be about 0.1 Fr, about 0.2 Fr, about 0.3 Fr, about 0.4 Fr, about 0.5 Fr, about 0.6 Fr, about 0.7 Fr, about 0.8 Fr, about 0.90 Fr, about 1 Fr, about 2 Fr, about 3 Fr, about 4 Fr, or about 5 Fr. A sensor housing having a size of about 1 Fr may be useful for medical applications, for example, when the sensor is screwed through an arterial or venous catheter where a sensor was previously placed.

[0124] C. Sensor Sleeve In some variations, the sleeve can be used to assist in coupling the sensor housing to the elongate body (e.g., a catheter) of a device (e.g., a blood flow control device). In these variations, the sensor housing is coupled or otherwise secured to the sleeve and positioned around the elongate body to partially or fully surround the elongate body, whereby the sensor can be coupled to the elongate body as described above.

[0125] The sleeve can be configured to receive the elongate body, whereby the sensor housing, and thus the sensor, is coupled or integrated with the elongate body. The sleeve can include a lumen configured to receive the elongate body, an opening (e.g., a window) through which the sensor housing can be exposed, and in some variations, features to facilitate a gradual transition in stiffness between the elongate body and the sleeve.

[0126] In some variations, the sleeve can be sized and shaped such that the elongate body can be received within the sleeve. For example, the sleeve can have a cross-sectional shape corresponding to the cross-sectional shape of the elongate body and can include a lumen passing through the sleeve having a diameter larger than the outer diameter of the elongate body. For example, in some variations, the sleeve can be tubular. In some variations, the sleeve adds stiffness to the elongate body around the sensor received within the sleeve, thereby protecting the sensor from damage and isolating the sensor from sensitivity-related errors that can occur due to bending of the elongate body.

[0127] The sleeve can be made from any suitable biocompatible polymer. For example, the sleeve can be formed from polymers such as, for example, polytetrafluoroethylene (PTFE), polyimide, Pebax®, thermoplastic polymers, and combinations thereof. Exemplary thermoplastic polymers can be, for example, polycarbonate, and polycarbonate / acrylonitrile-butadiene-styrene terpolymer blends. In some variations, the sleeve can be formed from metal, such as, for example, stainless steel, bondable metal alloys, or combinations thereof. In one variation, the sleeve includes stainless steel.

[0128] In some variations, the sleeve can include features that can allow for a gradual transition in stiffness of the elongated body and can distribute undesirable external forces (such as, for example, bending forces) acting on the elongated body. For example, in some variations, the sleeve can be stiffer than the elongated body and / or the combination of the elongated body and the sleeve can, together, make the portion of the device with the sleeve stiffer than the portion of the elongated body without the sleeve. In these variations, the sleeve can include slits and / or openings to facilitate the transition between the portion of the device with and without the sleeve. The slits or openings can be formed in any suitable shape or pattern, such as, for example, a spiral shape. In some variations, the slits and / or openings can be positioned only in the transition zone on the sleeve (such as, for example, one or both ends of the sleeve), while in other variations, the slits and / or openings can extend along the entire length of the sleeve. The transition zone can facilitate a gradual transition from a less rigid elongated body segment to a more rigid sleeve portion. This can provide the advantage of distributing bending forces, particularly when the elongated body is bent.

[0129] The sleeve may comprise one or more sleeve openings, which in some variations may receive at least a portion of the sensor housing and / or the sensor therein and may expose a portion of the sensor housing and thus at least a portion of the sensor positioned therein. The portion of the sensor and / or the portion of the sensor housing may be aligned with the sleeve opening to expose the sensor. For example, the portion of the sensor and / or the portion of the sensor housing may be aligned with the sleeve opening along the depth of the sleeve. For example, the portion of the sensor and / or the portion of the sensor housing may be positioned below the sleeve opening and axially aligned with the opening. In some variations, a portion of the sensor housing (e.g., a structural component) may pass through the sleeve opening and may be utilized to secure the sensor housing to the sleeve.

[0130] The sensor housing and / or the sensor may be inserted and / or positioned within the sleeve such that the sensor housing is located within the lumen of the sleeve. Thus, the sleeve and the sensor housing may be configured such that at least a portion of the sensor housing and / or the sensor (e.g., the surface of the sensor) may be aligned with the outer surface of the elongated body. Stated another way, the sensor housing and / or the sensor may be inserted into the sleeve at a depth selected to allow the sensor housing and / or the sensor to be aligned with the outer surface or side wall of the elongated body. The sensor housing and / or the sensor may be aligned with the outer surface or side wall of the elongated body such that they are in the same plane. The sleeve opening may allow the sensor to be exposed to the conditions within the patient's body to obtain measurements while the sensor remains protected within the sensor housing. In some variations, the elongated body may include an elongated body opening, window, and / or cavity for receiving the sensor housing.

[0131] In some variations, instead of a window, the sleeve may comprise one or more sleeve recessed portions configured to receive at least a portion of the sensor housing therein. When the sleeve is coupled to the elongated body, the sleeve recessed portions may be aligned with the opening and / or window of the elongated body. The sensor housing may be inserted and / or positioned within the sleeve recessed portions and then it may be received within the opening and / or window of the elongated body. In this way, the sensor housing may be received within the opening and / or window on the elongated body so as to be aligned with the outer surface or sidewall of the elongated body. In some variations, the sensor may not be housed or encapsulated within the sensor housing. Rather, the sensor may be inserted and / or positioned within the sleeve such that the sensor is located within the lumen of the sleeve and at least a portion of the sensor may be aligned with the outer surface of the elongated body. In such variations, an adhesive may be applied along the perimeter of the sensor to additionally secure the sensor to the sleeve. For example, the sleeve may further comprise one or more holes to provide an access point for applying an adhesive to secure the sensor to the sleeve. In some variations, one or more holes within the sleeve may be used to provide an access point for introducing an adhesive in an amount to fully or partially encapsulate the sensor within the sensor housing.

[0132] FIG. 19 depicts an exemplary variation of sensor 1900 and sensor housing 1902 attached to an elongated body 1904 via a sensor sleeve 1906. Referring to FIG. 19, sleeve 1906 may include a sleeve opening 1908 that receives a portion of sensor housing 1902 and exposes a portion of sensor 1900 housed within sensor housing 1902. The portion of sensor housing 1902 may be inserted and / or positioned within sleeve opening 1908, and the remaining portion of sensor housing 1902 may be located within the lumen (not shown in FIG. 19) of sleeve 1906. In this way, the sensing surface of sensor housing 1902 and / or sensor 1900 may be aligned with the outer surface or sidewall of elongated body 1904. As previously mentioned herein, sensor 1900 is encapsulated (e.g., fully contained within a polymer) within sensor housing 1902 using a polymer (e.g., RTV silicone) and / or otherwise sealed in order to minimize changes in sensor readings with respect to bending forces acting on the sensor and / or to protect the electrical components of the sensor from moisture, fluid intrusion, etc. In some cases, a hydrophobic polymer coating (e.g., parylene coating) may be applied to protect against moisture and / or fluid intrusion. The physiological state configured to be measured by the sensor may be transmitted to sensor 1900 through the polymer.

[0133] Method Also described herein are methods for measuring physical properties using the devices and systems described herein. In particular, the systems, devices, and methods described herein may be used to accurately measure parameters with a fewer number of steps and a compact circuit configuration form factor. Generally, the methods described herein include generating a plurality of output clock signals using an input clock signal and an adjustable delay. The difference between the output clock signals corresponds to the measured parameter.

[0134] FIG. 6 depicts a flowchart illustrating a variation of a method 600 for measuring a parameter. In the variation depicted in FIG. 6, the method 600 for measuring a parameter may include receiving an input clock signal at step 602.

[0135] At step 604, a first output clock signal having a predetermined ratio between the input clock signal and the first output clock signal may be generated using an adjustable delay. In some variations, the frequency of the first output clock signal may be greater than the frequency of the input clock signal.

[0136] At step 606, a second output clock signal may be generated using an adjustable delay. In some variations, the frequency of the second output clock signal may be greater than the frequency of the input clock signal.

[0137] In some variations, the first output clock signal may vary based on a first set of parameters, and the second output clock signal may vary based on a second set of parameters different from the first set of parameters. For example, the second set of parameters may include the first set of parameters and at least one additional parameter (e.g., the parameter of interest being measured). In some variations, the first set of parameters may comprise one or more of temperature and voltage. For example, the second set of parameters may include one or more of temperature, voltage, and force, pressure, light amplitude, sound amplitude, and resistance or capacitance corresponding to a chemical or physical reaction.

[0138] At step 608, a third signal may be generated based on the difference between the first output clock signal and the second output clock signal. In some variations, the third signal may correspond to one or more of temperature, voltage, force, pressure, light amplitude, and sound amplitude.

[0139] Optionally, in step 610, the third signal may be output as a digital signal. For example, the third signal may be output as a set of binary-encoded bits at a periodic rate.

[0140] Optionally, in step 612, the method may include generating a fourth output clock signal using an adjustable delay, and optionally, in step 614, may further include generating a fifth signal based on a difference between the first output clock signal and the fourth output clock signal. In some variations, the fifth signal may correspond to one or more of temperature, voltage, force, pressure, optical amplitude, and acoustic amplitude.

[0141] Optionally, in step 618, the method may further include outputting the fifth signal as a digital signal. For example, the fifth signal may be output as a set of binary-encoded bits at a periodic rate.

[0142] FIG. 12 depicts a flowchart of an exemplary method 1200 for determining a value associated with a physical parameter of interest in a sensor. At step 1202, a first count number indicative of the oscillation frequency in a first ring oscillator circuit during a sample period is obtained. The first ring oscillator circuit may be associated with (e.g., included in) the sensor and may oscillate at a first oscillation rate. The first oscillation rate may be based on a first set of physical parameters and a second physical parameter (i.e., the physical parameter of interest). At step 1204, a second count number indicative of the oscillation frequency in a second ring oscillator circuit during the sample period is obtained. The second ring oscillator circuit may be associated with (e.g., included in) the sensor and may oscillate at a second oscillation rate (e.g., different from the first oscillation rate). The second oscillation rate may be based only on the first set of physical parameters that do not include the second physical parameter. The first ring oscillator circuit may include a parameter-based delay circuit associated with the second physical parameter, while the second ring oscillator circuit does not include a parameter-based delay circuit associated with the second physical parameter. At step 1206, a value associated with the second physical parameter in the sensor is determined based on the first count number and the second count number.

[0143] Another method is related to daisy chain connection, as discussed, for example, in FIGS. 14A and 14B. In some variations, the methods described herein may include using a first sensor (e.g., sensor 1402) to measure a first value (e.g., a pressure value) for a first parameter (e.g., pressure), and transmitting the first value to a second sensor (e.g., sensor 1404) coupled to the first sensor. The method may further include using the second sensor to measure a second value (e.g., a pressure value, a force value, etc.) for a second parameter (e.g., pressure, force, etc.) that may be the same as or different from the first parameter, and generating a serial value that includes the first value and the second value. For example, the serial value may be a concatenation of the representations of the first value and the second value. In some variations, the serial value may be a first serial value, and the method may further include transmitting the first serial value to a third sensor (e.g., sensor 1406) coupled to the second sensor, measuring a third value (e.g., a pressure value, a force value, a light value, etc.) for a third parameter (e.g., pressure, force, light, etc.) that may be the same as or different from one or more of the first parameter and the second parameter using the third sensor, and generating a second serial value that includes the first serial value and the third value. In some variations, the method may further include transmitting the first and / or second serial value to a computing device configured to determine the first value, the second value, the third value, etc. based on the serial output. In some variations, the first sensor and the second sensor may be operably coupled to the computing device via only four signals, which are a power signal (e.g., VCC in FIG. 14A), a clock signal (e.g., CLK in FIG. 14A), a ground signal (e.g., GND in FIG. 14A), and an output signal (e.g., SER OUT in FIG. 14A).

[0144] Exemplary Sensors FIG. 7A is a schematic diagram of an exemplary variation of a sensor 700 comprising an FPGA circuit and a controller (e.g., a microcontroller). The FPGA circuit may comprise a first oscillator ring circuit and a second oscillator ring circuit configured to measure pressure. The first oscillator ring circuit may be disposed entirely on a single substrate (e.g., entirely on a single chip) and may function as a primary offset compensator. The second oscillator ring circuit may comprise a set of pins (e.g., two pins) on the FPGA having a first pin coupled to a piezoresistor and a second pin input to the same resistor. The input of the FPGA may be coupled to an input clock signal (e.g., 32.768 kHz) output from the microcontroller. The digital output of the FPGA may be coupled to the UART input of the microcontroller.

[0145] FIG. 7B is an example of a schematic diagram of a circuit 710 that may be included in an FPGA (e.g., the FPGA from FIG. 7A), and / or a chip, etc. The circuit includes a first oscillator ring circuit (ring #1) and a second oscillator ring circuit (ring #2). The first oscillator ring circuit and the second oscillator ring circuit each oscillate at their respective frequencies (e.g., represented by 18 bits, represented by 19 bits, etc.). The difference between the two rings is that ring #2 oscillates at a rate that depends on an external delay element (whereas ring #1 does not oscillate at a rate that depends on an external delay element), and the external delay element is configured to have a delay that varies based on a physical parameter of interest (the applied pressure in this example). The 32,768 Hz clock is (1) divided by 128 in a first clock divider circuit to generate a 256 Hz signal, and (2) divided by 4 in a second clock divider circuit to generate an 8,192 Hz signal. The 8,192 Hz signal may be associated with a shift signal in a 38-bit output resistor, and the 256 Hz signal may be associated with a latch signal in the 38-bit output resistor. The 256 Hz signal may also be used to reset an 18-bit counter (e.g., at each rising edge or each falling edge). The 38-bit output resistor may receive the outputs from both 18-bit counters and generate a signal for sending to the UART.

[0146] FIG. 7C is an example of a schematic diagram of a circuit 720 that may be included in an FPGA (e.g., the FPGA from FIG. 7A), and / or a chip, etc. The circuit includes a first oscillator ring circuit (Ring #1) and a second oscillator ring circuit (Ring #2). The first oscillator ring circuit and the second oscillator ring circuit each oscillate at their respective frequencies (e.g., represented by 18 bits, represented by 19 bits, etc.). The difference between the two rings is that Ring #2 oscillates at a rate that depends on an external delay element (whereas Ring #1 does not oscillate at a rate that depends on an external delay element), and the external delay element is configured to have a delay that varies based on a physical parameter of interest (the applied pressure in this example). A 32,768 Hz clock is divided by 128 in (1) a first clock divider circuit to generate a 256 Hz signal and divided by 2 in (2) a second clock divider circuit to generate a 16,384 Hz signal. The 16,384 Hz signal may be associated with a shift signal in a 48-bit output resistor, and the 256 Hz signal may be associated with a latch signal in the 48-bit output resistor. In some implementations, the 48-bit output resistor may have 38 bits associated with two 19-bit counters that may be formed into 5 bytes (8 bits each), and 48 bits that are the sum of a start bit and a stop bit for each of the 5 bytes, for a total of 48 bits. The 256 Hz signal may also be used to reset the 19-bit counter (e.g., at each rising edge or each falling edge). The 48-bit output resistor may receive the outputs from both 19-bit counters and generate a signal for sending to a UART.

[0147] Exemplary Systems and Devices The systems and devices described herein are not particularly limited and can be used in various industries and applications. For example, the systems and devices can be used with medical devices, such as systems and devices for monitoring a patient's physiological state and / or physiological state during a medical procedure, or alternatively can be incorporated into a medical device. In some variations, these systems include an elongated body (e.g., a catheter) with one or more sensors described herein for monitoring a physiological state during a medical procedure and / or for monitoring a patient's physiological functions over a long period of time during daily and critical medical procedures. In some cases, these systems can include a blood flow control device. In some variations, the device can be used to measure (or monitor) blood pressure. In these variations, the device can be configured to measure blood pressure at any location within the body. For example, the device can be placed within the central arterial vasculature (e.g., the aorta, pulmonary artery) or central venous vasculature (e.g., the vena cava), or the peripheral arterial vasculature (e.g., the femoral artery, radial artery) or peripheral venous vasculature (e.g., the femoral vein, radial vein), and used to measure the blood pressure therein. In one variation, the device can measure the blood pressure within the aorta. In another variation, the device can measure the blood pressure within the radial artery. The pressure measurement may or may not be performed using a device that includes an expandable member, such as an expandable balloon.

[0148] I. Exemplary Blood Flow Control Devices FIG. 8 illustrates an exemplary variation of the blood flow control device 804. The blood flow control device 804 may include an elongate body 802, an expandable member 810 (e.g., a balloon) coupled to the elongate body 802 and configured to be disposed within a blood vessel (e.g., the aorta), and one or more sensors (e.g., 811a, 811b) coupled to the shaft of the elongate body 802 (e.g., integrated with / within the shaft). The one or more sensors may be any of the sensors described herein (e.g., sensor 302, sensor chip 1120) and may be coupled to the shaft of the elongate body in any suitable manner (e.g., integrated with / within it). For example, in some variations, the one or more sensors may be housed within a sensor housing and / or coupled to the elongate body via a sleeve. The blood flow control device 804 may be coupled to a controller 812 (e.g., controller 320, microcontroller chip 1130), which may be operably coupled to the one or more sensors and a pump (e.g., a syringe pump). In some variations, the controller 812 may instead be included in a chip having the one or more sensors. The pump may be used to expand and contract (e.g., inflate and deflate) the expandable member. In some variations, the blood flow control device may include a plurality of sensors such as, for example, a first sensor proximal to the expandable member, a second sensor distal to the expandable member, and a third sensor configured to measure a parameter within or of the expandable member in a different manner. In some variations, each of the plurality of sensors may be configured to measure pressure (e.g., the proximal sensor may measure the pressure proximal to the expandable member, the distal sensor may measure the pressure distal to the expandable member, and the expandable member sensor may measure the pressure within the expandable member).

[0149] A. Expandable Member The expandable member 810 can be one of those disposed, coupled, integrated, attached, and / or fixed on the shaft of the elongated body 802, and the size of the expandable member 810 can be controllable by a controller or a user. For example, the expandable member 810 can be configured to expand and contract and / or inflate and deflate such that the size (e.g., volume) of the expandable member 810 can change during the use of the blood flow control device. During use, the blood flow can be regulated or otherwise controlled by changing the size of the expandable member 810, thereby changing the area of the blood vessel occluded by the expandable member 810. Fluid and / or compressed gas can be delivered through one or more lumens within the elongated body 802 to control and / or adjust the size (e.g., volume) of the expandable member 810. Thus, in some variations, the expandable member 810 can be strategically placed within the patient's aorta, and the size of the expandable member 810 can control the blood flow through the patient's aorta such that the distal blood flow of the expandable member 810 can be obstructed to increase the blood pressure proximal to the expandable member 810. The outer surface of the expandable member 810 can be configured to contact or otherwise engage the wall of the patient's blood vessel (e.g., at full occlusion). The expandable member 810 can include any suitable elastomeric material (e.g., polyurethane, silicone, etc.). Alternatively, the expandable member can comprise polyester, nylon, etc. In some variations, the expandable member 810 can comprise a shape memory material.

[0150] B. Sensor The blood flow control device may comprise a sensor of any of the variations described herein. For example, in some variations, the blood flow control device may comprise one or more (e.g., two, three, four, or more) pressure sensors of any of the variations described herein that are integrated into the elongate body 802. In some variations, the pressure sensor may be integrated into the elongate body 802 using a sleeve, as previously described herein. The distal sensor, whose position is indicated by reference numeral 811b, may be disposed between the tip of the elongate body 802 and the expandable member 810. The proximal sensor, whose position is indicated by reference numeral 811a, may be disposed between the base of the elongate body 802 (where the elongate body 802 is coupled to the device controller 812) and the expandable member 810. Each of the distal sensor and the proximal sensor may measure the patient's physiological state, such as physiological information indicating blood flow through the aorta, to determine the patient's underlying physiological function.

[0151] In some variations, the distal sensor 411b may be integrated proximally to the expandable 810 member, while the proximal sensor 811a may be integrated distally to the expandable member 810. For example, the distal sensor 811b located on the proximal side of the expandable member 810 may be positioned at a distance from the expandable member 810 so that physiological data collected from the distal sensor 811b is not disrupted by the blood flow downstream of the expandable member 810. In some variations, the distal sensor 811b may be positioned about 30 mm to about 10 mm, about 25 mm to about 15 mm, about 22 mm to about 18 mm from the expandable member 810. For example, the distal sensor 811b may be positioned about 20 mm from the expandable member 810. In some variations, the proximal sensor 811a located on the distal side of the expandable member 810 may be positioned about 30 mm to about 10 mm, about 25 mm to about 15 mm, or about 22 mm to about 18 mm from the expandable member. For example, the proximal sensor 811a may be positioned approximately 20 mm from the expandable member 810. As discussed above, in some variations, the sensors on the elongate body 402 may be positioned at a specific distance from the ends of the expandable member 810 to obtain physiological data upstream and downstream of the expandable member 810.

[0152] It should be noted that the terms "proximal" and "distal" as used herein with respect to a sensor and / or a particular local blood pressure reading refer to the direction of blood flow from the heart. That is, "proximal" is closer to the heart, while "distal" is farther from the heart. This is to avoid confusion with the reverse usage of the terms when explained from the perspective of a medical device such as a catheter. The "distal end" of a medical device is generally understood as the end at the expandable element 810 that is farthest from the device controller 812, and the "proximal end" is understood as the end closer to the operator.

[0153] In some variations, the blood flow control device may further include an expandable member sensor (not shown in FIG. 8) integrated into the elongated body 802. For example, the expandable member sensor may be integrated into the expandable member 810 or into the elongated body 802 within the expandable member 810. In variations where the expandable member sensor is coupled to the elongated body 802, the sensor may be coupled or integrated into the elongated body 802 using any of the sensor integration configurations and / or structures described herein (e.g., sensor housing, sensor sleeve, etc.). In some variations, the expandable member sensor may be coupled to, integrated with, and / or disposed on the device controller 812 and may be fluidly coupled to the expandable member. The expandable member sensor may be any one of the sensors described herein and may be configured to detect the characteristics of the expandable member.

[0154] C. Controller The blood flow control device 804 may include or be coupled to one or more controllers. For example, the blood flow control device 804 may include a device controller 812 coupled to the base of the elongated body 802. The device controller 812 may be communicatively coupled to one or more sensors such as, for example, a proximal sensor, a distal sensor, and / or an expandable member sensor. For example, the device controller 812 may be electronically coupled to a proximal sensor, a distal sensor, and / or an expandable member sensor.

[0155] The blood flow control system may include a system controller coupled to a blood flow control device (e.g., the blood flow control device 804 of FIG. 8). FIG. 21 illustrates an exemplary variation of the blood flow control system 2100. In some variations, the blood flow control system 2100 may include a system controller 2106 in addition to a device controller 2112 (e.g., the device controller 812 of FIG. 8). The system controller 2106 may be coupled to the blood flow control device 804, for example, via the device controller 2105 or, in variations without the device controller 2105, directly via the elongate body 2102.

[0156] In some variations, the device controller 2105 may further include a position sensor communicably coupled to a pump 2108 (further described below). In some variations, the position sensor may measure the position of a portion of the pump 2108. For example, the position sensor may measure the position of the plunger of the syringe pump 2108. The position of a portion of the pump 2108 may be used to infer the amount of fluid delivered to and / or removed from the expandable member 2110.

[0157] Additionally or alternatively, the device controller 2105 may comprise a motion sensor (e.g., an encoder such as a magnetic encoder, an optical encoder, etc.) communicatively coupled to the pump. When the pump 2108 is operated using a motor, the encoder may monitor the movement of the motor that may be used to determine the amount of expansion and / or contraction in the expandable member 2110. In some variations, the motion sensor may be a magnetic encoder. Additionally or alternatively, the motion sensor may be an optical encoder. Additionally or alternatively, at least a portion of the system controller 2106 may comprise an optical sensor and / or a contact sensor. The optical sensor and / or the contact sensor may be operatively coupled to a portion of the pump 2108 to determine the position of the pump 2108 and / or track its movement. The amount of expansion and / or contraction in the expandable member 2110 may be determined based on the position and / or movement of the pump 2108. In some variations, a flow sensor may be used to determine the amount of expansion and / or contraction in the expandable member 2110.

[0158] D. Pump As depicted in FIG. 21, the blood flow control system 2100 may comprise a pump 2108 that may be operatively coupled to the expandable member 2110 to facilitate sizing thereof. The pump 2108 may be housed within the housing of the device controller 2105 or the system controller 2106 (e.g., within an open or closed cavity or chamber), or otherwise held or coupled by the housing and communicatively coupled to one or both of the device controller 2105 or the system controller 2106. The pump 2108 may comprise or otherwise be coupled to an elongate member having a lumen (e.g., a conduit), which in turn may be coupled to the lumen (e.g., an inlet or an inflation lumen) of the elongate body of the blood flow control device. In this way, the pump 2108 may be in fluid communication with the expandable member 2110.

[0159] In some variations, the pump can be fluidly coupled to a valve (e.g., a stopcock valve) that can regulate the flow of fluid and / or compressed gas to the expandable member 2110. The size (e.g., volume) of the expandable member can be adjusted using the system controller and / or device controllers 2106, 2105, and the pump 2108.

[0160] The sensors described herein can be configured to measure one or more pressures (e.g., blood pressure, expandable member pressure) to determine a patient's physiological state or condition. A controller (e.g., a device controller and / or a system controller) communicatively coupled to the sensor can be configured to receive from the sensor data indicative of the patient's physiological state and / or the pressure associated with the expandable member. The controller can compare the received data to target data and adjust the volume of the expandable member to achieve the target data.

[0161] II. Exemplary Pressure Measurement Devices In some variations, any of the sensors described herein can be incorporated into a device and / or system configured to monitor (e.g., monitor alone, monitor without otherwise controlling blood flow) a patient's physiological state or parameter, such as blood pressure. As mentioned above, the sensors described herein can be placed in various arteries or veins to measure blood pressure. In other examples, the sensor can measure another parameter other than temperature or blood pressure. The sensor can be placed, for example, in the aorta, internal jugular vein, pulmonary artery, subclavian artery, femoral artery, radial artery, brachial artery, vena cava, internal jugular vein, or subclavian vein. The sensor can be included on or otherwise positioned within an elongate body (e.g., a catheter) coupled to a controller.

[0162] Any of the sensors described herein can be incorporated into a pressure measurement device. In some variations, the pressure measurement device can include a sensor within a sensor housing (as described herein), and the sensor housing can be attached to or otherwise integrated with an elongate body (e.g., a catheter). The elongate body that includes the sensor within the sensor housing can be introduced directly into the vasculature to measure pressure (e.g., blood pressure) or can be configured to advance through an existing arterial or venous line (e.g., a vascular access line). In some variations, the sensor can be assembled within a tubular housing (e.g., a hypodermic tube or catheter). The sensor and the tubular housing can be sized to allow passage of the elongate body into an artery or vein or through a vascular access line. The sensor can be formed to be physically small, e.g., on the order of about 0.1 Fr to about 5 Fr (including all values and subranges therein), and in some cases can be configured for integration into a tubular housing having a diameter in the range of about 0.1 Fr to about 10 Fr (including all values and subranges therein). For example, the sensor can have a size of about 0.1 Fr, about 0.2 Fr, about 0.3 Fr, about 0.4 Fr, about 0.5 Fr, about 0.6 Fr, about 0.7 Fr, about 0.8 Fr, about 0.90 Fr, about 1 Fr, about 2 Fr, about 3 Fr, about 4 Fr, or about 5 Fr. The diameter of the tubular housing can be about 0.1 Fr, about 0.2 Fr, about 0.3 Fr, about 0.4 Fr, about 0.5 Fr, about 0.6 Fr, about 0.7 Fr, about 0.8 Fr, about 0.90 Fr, about 1 Fr, about 2 Fr, about 3 Fr, about 4 Fr, about 5 Fr, about 6 Fr, about 7 Fr, about 8 Fr, about 9 Fr, or about 10 Fr. The small size of the sensor can allow space for other components of the pressure measurement device included in the elongate body, such as, for example, reinforcement members, fluid lumens, etc. The size and / or diameter of the sensor and the tubular housing will generally be selected based on the diameter of the elongate body, the vascular access line through which it is advanced, and / or the bend angle of the artery or vein through which it is passed. For example, when the elongate body is about 3 Fr or 4 Fr, the diameter of the sensor and / or the tubular housing can be about 1 Fr.The length of the tubular housing can be in the range of about 5 mm to about 15 mm (including all values and sub-ranges therein). For example, the length of the tubular housing can be about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, or about 15 mm.

[0163] The sensor housing can be attached to the elongated body of the pressure measurement device in various ways. For example, the sensor housing can be attached using one or more structural components (such as struts) as previously described. The sensor and the structural components can form a sensor assembly. For example, as shown in FIG. 20A, the sensor housing 2000 can be used to couple the sensor 2 to the elongated body 1. The sensor 2 can be encapsulated, for example, in a layer of polymer, such as RTV silicone or a different polymer, within the sensor housing 2000 by placing the sensor 2 on a polymer layer and then curing the polymer. Next, the sensor 2 can be encapsulated by covering the sensor 2 with an additional polymer, such as RTV silicone, and then curing the polymer. The polymer can have compliance that allows for the transmission of pressure signals through the polymer such that physiological conditions, such as blood pressure, can be transmitted through the polymer to the sensor 2. A separate seal 3 (such as an RTV silicone seal) can also be disposed within the tubular sensor housing 2000 to protect the sensor 2 from the effects of pressure. The sensor 2 and the sensor housing 2000 can collectively (as a sensor assembly) have a diameter sized to fit within the elongated body 1 and can be designed to have a small diameter (such as about 1 Fr). For example, as shown in the cross-sectional view of FIG. 20B, the sensor housing 2000 with the sensor 2 disposed therein can have a size of about 1 Fr and can be included within an elongated body (such as a catheter) 1 with a size of about 7 Fr. A pressure measurement device including a sensor and / or sensor housing of about 1 Fr integrated into a 7 Fr catheter can be useful when the device is placed within the aorta to measure internal blood pressure.

[0164] The sensors used in the pressure measurement device can be connected to the PCBA housing via one or more wires coupled to the sensor and one or more pins on a printed circuit board assembly (PCBA). For example, referring to FIGS. 20A and 22A, one or more wires (e.g., wire 4 in FIG. 20A) can be disposed within a conduit 6 and attached to the PCBA housing 7. The length of the conduit 6 can vary depending on the vascular access site and the target location within the artery or vein where the parameter (e.g., blood pressure) is measured. For example, the length of the conduit can range from about 35 cm to about 70 cm (including all values and sub - ranges therein). For example, the length of the conduit can be about 35 cm, about 40 cm, about 45 cm, about 50 cm, about 55 cm, about 60 cm, about 65 cm, or about 70 cm.

[0165] The PCBA housing can be configured to connect to a controller (e.g., a controller of a blood flow control system) and can include a PCBA network configured to control one or more functions of the sensor. The PCBA housing can comprise a top and a bottom. The top and the bottom can be connected via a hinge or an adhesive, or can be attached by snap - fit, friction fit, etc. The adhesive can be a tape (e.g., a foam tape) on one or more regions on the bottom portion of the housing. Any suitable adhesive can be used. Referring to FIG. 22B, a double - sided foam tape 9 can be included on two regions of the bottom portion 10 of the housing 7 to adhere the bottom portion 10 to the top portion 11. The top portion 11 of the housing 7 can also include a layer of double - sided foam tape 9 for attaching components of the PCBA network 8. A coupler (e.g., a silicone conduit) 12 can be included in the top portion 11 to connect the conduit (e.g., conduit 6 in FIG. 22A) extending from the sensor to the PCBA housing 7 and to connect the wires within the conduit 6 to the PCBA network 8. In some variations, the adhesive can also be used to secure the PCBA housing 7 to the patient's body. For example, the PCBA housing 7 can be provided on a patch having an adhesive surface configured to adhere the housing to a part of the patient's body, such as the skin of the patient's leg, arm, or torso.

[0166] The above-described variations have been described in some detail by way of illustration and example for purposes of clarity and understanding, but it will be apparent that certain changes and modifications can be made and are intended to fall within the scope of the appended claims. Additionally, it should be understood that the components and features of the systems and devices described herein can be used in any combination. The description of specific elements or features with respect to specific figures is not intended to be limiting and should not be construed as suggesting that the element cannot be used in combination with any of the other described elements. For all of the variations described herein, the method steps may not be executed sequentially. Some steps may be optional, and not all of the steps of the method may be executed.

Claims

1. It is a sensor, A first circuit configured to receive an input clock signal and output a first output count signal at a predetermined sample rate, A different second circuit, configured to receive the input clock signal and output a second output count signal at a predetermined sample rate, A sensor comprising: a third circuit coupled to the first circuit and the second circuit, the third circuit configured to generate a third signal based on the first output count signal and the second output count signal.

2. The sensor according to claim 1, wherein the first output count signal changes based on a first set of parameters, and the second output count signal changes based on a second set of parameters different from the first set of parameters.

3. The sensor according to claim 2, wherein the first parameter set includes one or more of temperature and voltage.

4. The sensor according to claim 2, wherein the second set of parameters includes temperature, voltage, and one or more of force, pressure, light amplitude, sound amplitude, radiation, and resistance or capacitance corresponding to a chemical or physical reaction.

5. The sensor according to claim 1, wherein the third signal corresponds to one or more of temperature, voltage, force, pressure, light amplitude, and sound amplitude.

6. The sensor according to claim 1, wherein the frequency of the predetermined sample rate is less than the frequency of the input clock signal.

7. The sensor according to claim 1, wherein the first circuit comprises a first plurality of delay circuits arranged in a ring configuration, and the second circuit comprises a second plurality of delay circuits arranged in another ring configuration.

8. The sensor according to claim 7, wherein the first plurality of delay circuits comprises a first plurality of inverter circuits, the second plurality of delay circuits comprises a second plurality of inverter circuits, and the second plurality of delay circuits are different from the first plurality of delay circuits.

9. The sensor according to claim 8, wherein the first circuit comprises a first counter and a first latch, and the second circuit comprises a second counter and a second latch.

10. The sensor according to claim 8, wherein the first plurality of inverter circuits are coupled to a first multiplexer, and the second plurality of inverter circuits are coupled to a second multiplexer.

11. The sensor according to claim 8, wherein the first plurality of inverter circuits and the second plurality of inverter circuits are configured in a closed loop having positive feedback.

12. The sensor according to claim 7, wherein the first plurality of delay circuits comprises a first resistor-capacitor delay circuit.

13. The sensor according to claim 1, wherein the second circuit comprises one or more of the resistor-capacitor delay circuit, the resistor-inductor delay circuit, and the capacitive delay circuit.

14. The sensor according to claim 1, wherein the first circuit comprises a first oscillator circuit, and the second circuit comprises a second oscillator circuit.

15. The sensor according to claim 1, further comprising a fourth circuit coupled to the third circuit, the fourth circuit configured to receive the input clock signal and output a fourth output count signal at a predetermined sample rate, and the third circuit configured to generate a fifth signal based on the difference between the first output count signal and the fourth output count signal.

16. The sensor according to claim 15, wherein the fifth signal corresponds to one or more of temperature, voltage, force, pressure, light amplitude, and sound amplitude.

17. The sensor according to claim 1, further comprising a substrate having the first circuit, the second circuit, and the third circuit.

18. A first circuit board comprising the first circuit and the second circuit, The sensor according to claim 1, further comprising a second substrate having the third circuit.

19. The sensor according to claim 1, further comprising a fourth circuit configured to output the third signal as a digital signal.

20. The sensor according to claim 1, further comprising a fourth circuit configured to output the third signal as a set of binary encoded bits at a periodic rate.

21. The sensor according to claim 20, wherein the fourth circuit comprises one or more of a wire and an antenna.

22. A method for measuring parameters, Receiving the input clock signal, The first circuit generates a first output count signal at a predetermined rate based on receiving the input clock signal, A second circuit, different from the first circuit, receives the input clock signal and generates a second output count signal at the predetermined rate; A method comprising generating a third signal based on the first output count signal and the second output count signal.

23. The method according to claim 22, wherein the third signal represents a sensor value indicating the parameter.

24. The method according to claim 22, wherein the first output count signal changes based on a first set of parameters, and the second output count signal changes based on a second set of parameters different from the first set of parameters.

25. The first set of parameters includes temperature and voltage, The second set of parameters includes temperature, voltage, and pressure. The method according to claim 24, wherein the parameter is pressure.

26. A device configured to monitor blood pressure, The long, slender body, A device comprising: a sensor according to claim 1, disposed within a tubular sensor housing connected to the elongated main body.

27. ​​A sensor for measuring parameters of the environment surrounding the sensor, A first circuit configured to receive an input clock signal and output a first output count signal at a predetermined sample rate, A second circuit configured to receive the input clock signal and output a second output count signal at the predetermined sample rate, A sensor comprising: a third circuit coupled to the first circuit and the second circuit, the third circuit configured to generate a third signal representing a sensor value indicating the parameter based on the first output count signal and the second output count signal.

28. The sensor according to claim 27, wherein the first output count signal changes based on a first set of parameters, and the second output count signal changes based on a second set of parameters different from the first set of parameters.

29. The first set of parameters includes one or more of temperature and voltage, The sensor according to claim 28, wherein the second set of parameters includes temperature, voltage, and one or more of force, pressure, light amplitude, sound amplitude, radiation, and resistance or capacitance corresponding to a chemical or physical reaction.

30. The sensor according to claim 27, wherein the first circuit comprises a first plurality of delay circuits arranged in a ring configuration, and the second circuit comprises a second plurality of delay circuits arranged in another ring configuration.

31. The sensor according to claim 30, wherein the first plurality of delay circuits comprises a first plurality of inverter circuits, the second plurality of delay circuits comprises a second plurality of inverter circuits, and the second plurality of delay circuits are different from the first plurality of delay circuits.

32. The sensor according to claim 31, wherein the first plurality of inverter circuits are coupled to a first multiplexer, and the second plurality of inverter circuits are coupled to a second multiplexer.

33. The sensor according to claim 31, wherein the first plurality of inverter circuits and the second plurality of inverter circuits are configured in a closed loop having positive feedback.

34. The sensor according to claim 27, wherein the first circuit comprises a first counter and a first latch, and the second circuit comprises a second counter and a second latch.

35. The sensor according to claim 27, further comprising a fourth circuit coupled to the third circuit, the fourth circuit configured to receive the input clock signal and output a fourth output count signal at a predetermined sample rate, and the third circuit configured to generate a fifth signal based on the difference between the first output count signal and the fourth output count signal.

36. A first substrate comprising the first circuit and the second circuit, The sensor according to claim 27, further comprising a second substrate having the third circuit.

37. A method for measuring parameters of the environment surrounding a sensor, Receiving the input clock signal, Using the first circuit, a first output count signal is generated at a predetermined rate based on the input clock signal. Using the second circuit, a second output count signal is generated at the predetermined rate, A method comprising generating a third signal representing a sensor value indicating the parameter based on the first output count signal and the second output count signal.

38. The method according to claim 37, wherein the parameter corresponds to one or more of temperature, voltage, force, pressure, light amplitude, and sound amplitude.

39. The method according to claim 37, wherein the first output count signal changes based on a first set of parameters, and the second output count signal changes based on a second set of parameters different from the first set of parameters.

40. The first set of parameters includes temperature and voltage, The second set of parameters includes temperature, voltage, and pressure. The method according to claim 39, wherein the parameter is pressure.

41. The method according to claim 37, wherein the frequency of the predetermined rate is less than the frequency of the input clock signal.

42. The method according to claim 37, further comprising using a fourth circuit to output the third signal as a set of binary encoded bits at a periodic rate.

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