Apparatus and method for smart sensor applications

Abstract

The present invention relates to an apparatus and method for smart sensor applications. A device includes: a load resistor, which can be connected in series with an electronic sensor to form a series resistance of the load resistor and the internal impedance of the electronic sensor; an excitation circuit, which is configured to apply a predetermined voltage to a circuit element; and a measurement circuit, which is configured to start applying the predetermined voltage to the series resistor and determine the series resistance; start applying the predetermined voltage to the load resistor and determine the load resistance; and use the determined series resistance and the load resistance to calculate the internal impedance of the sensor, and provide the calculated internal impedance to a user or a processing program.

Description

[0001] This application is a divisional application of the invention patent application with the application date of January 8, 2018, application number 201880003803.9, and invention name “Device and method for smart sensor application”.

[0002] Priority declaration

[0003] This application claims priority to U.S. patent application No. 15 / 433,862, filed on February 15, 2017, which claims priority to PCT application No. PCT / CN2017 / 070608, filed on January 9, 2017, the entire contents of which are incorporated herein by reference. Technical Field

[0004] This document generally relates to interface circuits for electronic sensors. Some embodiments relate to test circuits for electronic sensors. Background Art

[0005] Smart sensors are electronic circuits that measure certain aspects of their environment and trigger computing resources to perform predefined functions in response to the measurements. Smart sensors are useful in applications such as implementing the Internet of Things (IoT). Sometimes, the output of a smart sensor needs to be customized for monitoring electronics operatively coupled to the smart sensor to obtain information about the computing resource. The present inventors have recognized a need for improved interface circuits for smart sensor circuits. Summary of the Invention

[0006] This document generally relates to interface circuits for electronic sensors.

[0007] Aspect 1 of the present disclosure includes subject matter (such as a test circuit for an electronic sensor) comprising: a load resistor that can be connected in series with an electronic sensor to form a series resistance of the load resistance and an internal impedance of the electronic sensor; an excitation circuit that is configured to apply a predetermined voltage to a circuit element; and a measurement circuit that is configured to initiate application of the predetermined voltage to the series resistance and determine the series resistance; initiate application of the predetermined voltage to the load resistance and determine the load resistance; and calculate the internal impedance of the sensor using the determined series resistance and the load resistance, and provide the calculated internal impedance to a user or a processing program.

[0008] In aspect 2, the subject matter of aspect 1 optionally includes an excitation circuit configured to apply a specified electrical signal having a signal amplitude less than 20 millivolts (20 mV) to the series resistor, and the internal impedance of the electronic sensor is less than 10 ohms (10Ω).

[0009] In aspect 3, the subject matter of one or both aspects 1 and 2 optionally includes the electronic sensor being an electrochemical sensor.

[0010] Aspect 4 includes subject matter (such as an integrated circuit) or, optionally, in combination with any combination of Aspects 1 to 3 to include subject matter comprising an excitation circuit configured to apply an excitation signal to a sensor circuit, wherein the excitation circuit comprises a configurable first circuit gain stage and a configurable second circuit gain stage, wherein in a first gain mode, the excitation circuit generates a first excitation signal from a test signal using a first signal gain applied by the first circuit gain stage and a second signal gain applied by the second circuit gain stage, and wherein in a second gain mode, the excitation circuit generates a second excitation signal from the test signal using a third signal gain applied by the first circuit gain stage and a fourth signal gain applied by the second circuit gain stage; and a measurement circuit configured to selectively initiate application of the first excitation signal or the second excitation signal to the electronic sensor and calculate an internal impedance of the sensor.

[0011] In aspect 5, the subject matter of aspect 4 optionally includes a measurement circuit configured to initiate application of the first excitation signal to the electronic sensor when the internal impedance of the sensor has a first internal impedance range, and to initiate application of the second excitation signal to the electronic sensor when the internal impedance of the sensor has a second internal impedance range, wherein the first internal impedance range is greater than the second internal impedance range.

[0012] In aspect 6, the subject matter of one or both of aspects 4 and 5 may optionally include the signal gain of the second gain circuit stage being 1 in the first gain mode and being less than 1 and greater than 0 in the second gain mode.

[0013] In aspect 7, the subject matter of one or any combination of aspects 4 to 6 may optionally include the signal gain of the first gain circuit stage being greater than 1 in the first gain mode and less than 1 and greater than 0 in the second gain mode.

[0014] In aspect 8, the subject matter of one or any combination of aspects 4 to 7 may optionally include a digital-to-analog converter (DAC) circuit configured to generate the test signal.

[0015] Aspect 9 includes subject matter (such as a test circuit) or can be optionally combined with one or any combination of Aspects 1 to 8 to include subject matter comprising: an adjustable bridge resistor and a calibration resistor for coupling to an electronic sensor; an excitation circuit configured to apply an excitation signal to the electronic sensor, the bridge resistor, and the calibration resistor; and a measurement circuit configured to apply a first excitation signal to the calibration resistor and measure a calibration current; apply the first excitation signal to the first bridge resistor and measure a first bridge current; apply a second excitation signal to the first bridge resistor and measure a second bridge current; apply the second excitation signal to the sensor and measure a sensor current; and calculate an internal impedance of the sensor using the calibration resistor, the calibration current, the first bridge current, the second bridge current, and the sensor current.

[0016] In aspect 10, the subject matter of example 9 can optionally include a multiplexer circuit configured to selectively apply an excitation signal to the calibration resistor, the adjustable bridge resistor, or the sensor.

[0017] In aspect 11, the subject matter of one or both of aspects 9 and 10 may optionally include a multiplexer circuit configured to apply an excitation signal to the calibration resistance, and the measurement circuit configured to calculate the calibration resistance using the excitation signal.

[0018] In aspect 12, the subject matter of one or any combination of aspects 9 to 11 may optionally include a measurement circuit configured to set the bridge resistance to a coarse bridge resistance value before applying the excitation signal to the bridge resistance.

[0019] In aspect 13, the subject matter of one or any combination of aspects 9 to 12 optionally includes a measurement circuit configured to apply a third excitation signal to the first bridge resistor and measure a third bridge current, apply the third excitation signal to the second bridge resistor and measure a fourth bridge current, and calculate an internal impedance of the sensor using the calibration resistor, the calibration current, the first bridge current, the second bridge current, the third bridge current, the fourth bridge current, and the sensor current.

[0020] In aspect 14, the subject matter of one or any combination of aspects 9 to 13 optionally includes the electronic sensor being an electrochemical sensor, and the resistance of the electronic sensor being indicative of a remaining useful life of the electrochemical sensor.

[0021] Aspect 15 includes subject matter such as an apparatus, or optionally, in combination with one or any combination of Examples 1 to 14, to include such subject matter having an integrated circuit. The integrated circuit includes an input for receiving an electrical signal from an electronic sensor, wherein the electrical signal includes a direct current (DC) offset and a varying signal component; a digital-to-analog converter (DAC) circuit configured to subtract the DC offset from the input signal; a programmable gain amplifier (PGA) operably coupled to the DAC circuit, wherein the PGA circuit is configured to apply a signal gain to the varying signal component of the input signal; and a measurement circuit configured to generate a measure of the varying signal component.

[0022] In aspect 16, the subject matter of aspect 15 may optionally include measurement circuitry comprising analog-to-digital converter (ADC) circuitry configured to generate a measure of the varying signal component.

[0023] In aspect 17, the subject matter of one or both of aspects 15 and 16 may optionally include measurement circuitry comprising a fast Fourier transform (FFT) circuit configured to measure a frequency response of the varying signal component.

[0024] In aspect 18, the subject matter of one or any combination of aspects 15 to 17 may optionally include an electronic sensor operatively coupled to the integrated circuit, wherein the electronic sensor is a resistive electronic sensor.

[0025] In aspect 19, the subject matter of one or any combination of aspects 15 to 18 optionally includes the electronic sensor being a gas sensor, and the electrical signal from the electronic sensor being proportional to the amount of gas in the atmosphere.

[0026] In aspect 20, the subject matter of one or any combination of aspects 15 to 20 optionally includes a detection circuit wherein the electronic sensor is an oxygen sensor, and wherein the detection circuit is configured to generate an indication of a lower explosive limit based on a measure of the varying signal component.

[0027] Aspect 21 may include any part or combination of any part of any one or more of Examples 1 to 20 or, optionally, be combined therewith to include a subject matter that may include an apparatus for performing one or more functions of Aspects 1 to 20 or a machine-readable medium including instructions that, when executed by a machine, cause the machine to perform any one or more functions of Aspects 1 to 20.

[0028] According to one aspect of the present disclosure, an integrated circuit is further provided, comprising: a sensor circuit; an excitation circuit configured to apply an excitation signal to the sensor circuit, wherein the excitation circuit comprises a configurable first circuit gain stage and a configurable second circuit gain stage, wherein in a first gain mode, the excitation circuit generates a first excitation signal from a test signal using a first signal gain applied by the first circuit gain stage and a second signal gain applied by the second circuit gain stage, and in a second gain mode, the excitation circuit generates a second excitation signal from the test signal using a third signal gain applied by the first circuit gain stage and a fourth signal gain applied by the second circuit gain stage; and a measurement circuit configured To selectively initiate application of a first excitation signal or a second excitation signal to a sensor circuit and calculate an internal impedance of the sensor circuit, a predetermined excitation signal is applied to the sensor circuit, a range of the internal impedance of the sensor circuit is determined, and a signal gain of one or both of a first circuit gain stage and a second circuit gain stage is selected based on the determined range of the internal impedance; and wherein the measurement circuit is configured to initiate application of the first excitation signal to the sensor circuit when the internal impedance of the sensor circuit has a first internal impedance range, and to initiate application of the second excitation signal to the sensor circuit when the internal impedance of the sensor circuit has a second internal impedance range, wherein the first internal impedance is greater than the second internal impedance range.

[0029] These non-limiting aspects can be combined in any arrangement or combination. This section is intended to provide an overview of the subject matter of this patent application. This is not intended to provide an exclusive or exhaustive explanation of the present invention. The detailed description is included to provide further information about this patent application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the accompanying drawings, which are not necessarily drawn to scale, like numbers may describe similar components in different views. Like numbers with different letter suffixes may represent different examples of similar components. By way of example, the accompanying drawings generally illustrate, in a non-limiting manner, various embodiments discussed in this document.

[0031] Figure 1A and 1B is a block diagram showing a test circuit and a sensor circuit.

[0032] Figure 2A and 2B is a block diagram illustrating another test circuit 204 electrically coupled to the sensor circuit.

[0033] Figure 3 is a flow chart of an example of a method of controlling a test circuit to measure the internal impedance of an electronic sensor.

[0034] Figure 4 is a circuit diagram of a portion of another example of a test circuit electrically coupled to a sensor circuit.

[0035] Figure 5 is a flow chart of another example of a method of controlling a test circuit to measure the internal impedance of an electronic sensor.

[0036] Figure 6 is a circuit diagram of a portion of another example of a test circuit electrically coupled to a sensor circuit.

[0037] Figure 7 is a flow chart of an example of a method of controlling a test circuit to measure the internal impedance of an electronic sensor.

[0038] Figure 8 is a circuit diagram of a portion of another example of a test circuit electrically coupled to a sensor circuit.

[0039] Figure 9 is an example of the output of a sensor circuit.

[0040] Figure 10 is a flow chart of an example of a method of controlling a test circuit to measure the internal impedance of an electronic sensor. DETAILED DESCRIPTION

[0041] Some smart sensor circuits may include electrochemical sensors to monitor the amount or concentration of gas. System requirements for sensors typically require that the sensor circuit have low power consumption and exhibit low noise to reduce errors. In order to maximize life and minimize service, it is also desirable that the monitoring circuit have low power consumption. This can present many challenges in designing circuits to monitor different types of smart sensor circuits. For example, it may be necessary to measure the impedance of the sensor circuit for diagnostic purposes, but smart sensors may have a wide range of internal impedances. A sensor may have an internal resistance greater than 10 kilo-ohms (10kΩ), while other sensors may have a low internal resistance (e.g., 1Ω). Sensors with low internal impedance typically require a higher voltage measurement signal to provide a sufficient signal-to-noise ratio (SNR). However, applying a higher voltage measurement signal to a low impedance may result in high current consumption of the measurement circuit, and the sensor circuit may sometimes be unable to withstand the current associated with the higher measurement.

[0042] Figure 1A and 1B is a block diagram of a test circuit 104 and a sensor circuit 106. The test circuit 104 may be included on an integrated circuit. To measure the internal impedance of the sensor circuit, an excitation signal is applied between the driver or "D" connection and the transimpedance amplifier (TIA) or "T" connection. The "P" and "N" connections are the sensing nodes of the sensor operation. To determine the internal impedance of the sensor circuit, the test circuit applies an excitation signal to the sensor circuit using the D and T connections. Figure 1AIn FIG. 1 , the excitation signal has a magnitude of fifteen millivolts (15 mV), and the sensor circuit 106 has an internal impedance of 181 Ω. Applying the excitation signal results in a current of 0.08 milliamperes (0.08 mA) passing through the sensor. The test circuit can use Ohm's law to determine the internal resistance of the sensor circuit. The test circuit can provide the determined internal impedance to a user (e.g., by presenting the value on a display) or to a processing program (e.g., a processing program that stores the value in a memory or takes some action using the determined impedance).

[0043] exist Figure 1B In this example, sensor circuit 106 has an internal resistance of 1Ω, but one might want to measure the sensor using the same 15mV excitation signal. However, applying the excitation signal directly results in a current of 15mA. This current can cause problems for a variety of reasons. For example, the current may be too large for the desired power consumption, or the sensor circuit may not be able to withstand the current of that magnitude. Furthermore, attempting to accommodate both a 0.08mA current and a 15mA current may lead to accuracy issues in the measurements made by the monitoring circuit. Lowering the excitation voltage can significantly reduce the SNR.

[0044] Figure 2A and 2B 2 is a block diagram of another example of a test circuit 204 electrically coupled to a sensor circuit 206. The test circuit can be used to determine the internal impedance of a sensor circuit having an internal impedance of approximately 200Ω, and also to determine the internal impedance of a sensor circuit having an internal impedance of less than 10Ω. The test circuit includes a load resistor R load , excitation circuit 208 and measurement circuit 210. The load resistor may have a resistance value of 100Ω (in some embodiments, the load resistor has a resistance value of approximately 200Ω). The measurement circuit may include logic circuitry that performs the functions described. In a variant, the measurement circuit includes a processor such as a microprocessor. Figure 2A In the embodiment of the present invention, when a sensor circuit having a low impedance is to be monitored, the measurement circuit 210 connects a load resistor in series with the internal impedance of the sensor circuit to form a series resistor. The excitation circuit 208 applies an excitation signal having a predetermined voltage to the series resistor. In a variation, the predetermined voltage is less than or equal to 20 mV. The measurement circuit uses the resulting current and the predetermined voltage to determine the series resistor. Figure 2B In the CMOS sensor circuit, the test circuit then applies only the excitation signal to the load resistor. The excitation signal uses the resulting current and a predetermined voltage to determine the load resistance. The test circuit determines the internal impedance of the sensor circuit by subtracting the load resistance from the series resistance.

[0045] Increasing the load resistance results in comparable internal impedances between the two sensor types. This improves the accuracy of the impedance value determined by the test circuit. In some examples, the measurement circuit calibrates the excitation signal to a predetermined voltage. A calibration resistor of predetermined resistance can be electrically connected to the output of the test circuit, and the test circuit can adjust the excitation signal until a specific current corresponding to the predetermined voltage of the excitation signal is measured.

[0046] Figure 3 1 is a flow chart of an example of a method 300 for controlling a test circuit to measure the internal impedance of an electronic sensor. At 305, a load resistor is electrically connected in series with the sensor to form a series resistance of the load resistor and the internal impedance of the sensor. At 310, an excitation signal having a predetermined voltage is applied to the series resistance, and the series resistance is determined (e.g., by Ohm's law). At 315, a predetermined voltage is applied to the load resistor and the load resistance is determined. At 320, the internal impedance of the sensor is determined using the determined load resistance and series resistance. The value of the internal impedance is provided to a user or a processing program. The method can be used for other ranges of internal impedance. For example, the test circuit can be used to measure the internal impedance of a sensor between approximately 1 kΩ and 1 Ω.

[0047] Figure 4 4 is a circuit diagram of an example portion of a test circuit 404 electrically coupled to a resistor (Rx) representing the internal impedance of a sensor circuit 406. Test circuit 404 may be included on an integrated circuit. Test circuit 404 includes a digital-to-analog converter (DAC) circuit 412, an excitation circuit 414, and a measurement circuit 416. To measure the internal impedance, a test signal is generated using the DAC circuit 412. Using an excitation operational amplifier 424, excitation circuit 414 applies an excitation signal generated using the test signal to the sensor circuit. Measurement circuit 416 uses a monitoring signal generated by the excitation to determine the internal impedance. For example, an excitation signal of a predetermined voltage may be applied to the sensor circuit, and the resulting current signal may be used to determine the internal impedance. DAC circuit 412 allows for the generation of excitation signals of varying frequencies and magnitudes, such as by controlling DAC circuit 412 using a processor or other control circuit (e.g., a waveform generator).

[0048] When the internal impedance to be measured is low, it may be necessary to reduce the voltage of the excitation signal to limit the current through the sensor and thus the power consumption of the test. The challenge in measuring the internal impedance of different types of sensors with very different internal impedances is that as the voltage of the excitation signal is reduced, the circuit noise can become significant.

[0049] Excitation circuit 414 includes a configurable first circuit gain stage 420 and a configurable second circuit gain stage 418. First circuit gain stage 420 includes a programmable gain amplifier (PGA). Second circuit gain stage includes resistor Rd and cross-coupling switch circuit 422. The gain of the first circuit stage can be configured by changing the programmable gain, and the gain of second circuit gain stage 418 can be configured by changing the state of cross-coupling switch circuit 422. The combined signal gain of excitation circuit 414 is configured by measurement circuitry (e.g., using a control circuit) based on whether the internal impedance of the sensor circuit to be measured is in a higher impedance range or a lower impedance range. When the internal impedance is in the higher impedance range, a higher signal gain is provided.

[0050] When the sensor circuit has an internal impedance value within a higher range, the excitation circuit 414 is configured to operate in a first gain mode. The excitation circuit generates a first excitation signal from the DAC circuit test signal using a first signal gain applied by the first circuit gain stage and a second signal gain applied by the second circuit gain stage. In an example not intended to be limiting, the gain of the first circuit gain stage 420 is 1, and the gain of the second circuit gain stage 418 is 2, providing an overall signal gain of 2 to the test signal in the first gain mode.

[0051] When the sensor circuit has an internal impedance value within the lower range, the excitation circuit 414 is configured to operate in a second gain mode. The excitation circuit generates a second excitation signal from the DAC circuit test signal using a third signal gain applied by the first circuit gain stage and a fourth signal gain applied by the second circuit gain stage. The gain in the second gain mode can be a gain value between 0 and 1. In an example, the gain of the first circuit gain stage 420 is one-tenth (1 / 10), and the gain of the second circuit gain stage 418 is one-half (1 / 2), providing an overall signal gain of one-twentieth (1 / 20) to the test signal in the second gain mode. The value of the signal gain provided by the second gain mode can be varied by changing the resistor values. In certain examples, the second gain stage provides a gain of 4 or 5 in the first gain mode and a gain of one-quarter (1 / 4) or one-fifth (1 / 5) in the second gain mode. The measurement circuit 416 selectively enables application of the first excitation signal or the second excitation signal to the electronic sensor and calculates the sensor's internal impedance. When the internal impedance is in the lower range, the small signal gain reduces the circuit noise of the PGA and the driver operational amplifier 424. This improves the accuracy of the internal impedance measurement in the lower range.

[0052] Figure 51 is a flow chart of an example method 500 of controlling a test circuit to measure the internal impedance of an electronic sensor. At 505, a first excitation signal in a first gain mode is applied to the sensor when the internal impedance of the sensor has a first internal impedance range. In the first gain mode, the first excitation signal is generated from a test signal using a first signal gain generated using a first circuit gain stage and a second signal gain generated using a second circuit gain stage.

[0053] At 510, when the internal impedance of the sensor has a second internal impedance range, a second excitation signal in a second gain mode is applied to the sensor. In some examples, the impedance values ​​in the second impedance range are lower than the impedance values ​​in the first impedance range. In the second gain mode, the second excitation signal is generated from the test signal using a third signal gain using the first circuit gain stage and a fourth signal gain using the second signal gain stage.

[0054] At 515, the internal impedance of the sensor is calculated using the first excitation signal when in the first gain mode, and the internal impedance of the sensor is calculated using the second excitation signal when in the second gain mode. The calculated internal impedance can be provided to a user or a processing program. The internal impedance range of the sensor circuit, and therefore the signal gain used to measure the sensor circuit, can be known in advance (e.g., by the type of sensor) and programmed by the user. In other examples, the measurement circuit can determine which signal gain to apply to the excitation circuit. In some examples, the sensor circuit includes an identifier (e.g., a machine-readable type code) that is read by the test circuit. In some examples, an excitation signal of a predetermined voltage is applied to the sensor circuit to determine a rough impedance measurement to determine the internal impedance range of the sensor circuit and to set the signal gain accordingly.

[0055] Figure 6 FIG6 is a circuit diagram of another example portion of a test circuit 604 electrically coupled to a sensor circuit 606. The test circuit may be included in an integrated circuit. In some examples, the sensor circuit and the test circuit are included in the same integrated circuit. The electronic sensor may be an electrochemical sensor or a gas sensor. The impedance of an electronic sensor may change with sensor use, and measuring the impedance of the sensor can be used to estimate the remaining useful life of the sensor. If the sensor is used to sense toxic substances or gases, determining when the sensor is nearing the end of its useful life may be more important.

[0056] Test circuit 604 includes excitation circuitry 614 and measurement circuitry 616. The excitation circuitry provides an excitation signal for measuring impedance. The measurement circuitry may include logic circuitry for performing the described functions and may include control circuitry for initiating measurements and calculations. To determine the unknown impedance of sensor circuit Rx, an excitation signal Vexc may be applied to the sensor circuit, and sensor current Ix may be measured, where Ix = Vexc / Rx. The same excitation signal Vexc is applied to a known calibration resistor 626 (Rcal), and calibration current Ical is measured, where Ical = Vexc / Rcal. Because Vexc is the same in both measurements, the unknown impedance of the sensor can be determined as Rx = Rcal(Ical / Ix).

[0057] This measurement method works well if the value of Rx is of the same order of magnitude as Rcal. However, if the sensor impedance differs significantly from Rcal, the method does not work well. For example, if Rcal is approximately 200Ω and Vexc is 1V, then Iexc is approximately 5 milliamperes (5mA). If Rx is 1 megohm (1MΩ), then Ix is approximately 1 microampere (1μA). These current values ​​are too different for the measurement circuit to provide the desired accuracy. Increasing the gain of the signal being measured may also increase the gain of the signal error, which can increase the error in the signal measurement.

[0058] In addition to the calibration resistors, Figure 6 The test circuit 604 also includes an adjustable bridge resistor 628. The bridge resistor is adjusted to a value between the Rcal resistance and the sensor impedance. The bridge resistor can be an inexpensive resistor circuit, and the resistance may not be known to the desired accuracy. The test circuit 604 can include a multiplexer circuit that can be used to selectively apply an excitation signal to the calibration resistor, the adjustable bridge resistor, or the sensor circuit 606.

[0059] A first predetermined excitation signal may be applied to Rcal and bridge resistor Rb, and a second predetermined excitation signal may be applied to bridge resistor Rb and sensor circuit Rx. Different signal gains may be applied to the separate excitation signals, and the measured current may be used to determine the impedance of the electronic sensor.

[0060] For example, the measurement circuit 616 may apply a first excitation signal Vexc1 to the calibration resistor Rcal and measure the calibration current Ical. A first excitation signal may be applied to the bridge resistor Rb and may measure a first bridge current Ib1. The measurement circuit 616 may apply a second excitation signal Vexc2 to the bridge resistor and may measure a second bridge current Ib2. A second excitation signal may be applied to the sensor and may measure the sensor current Ix. The impedance of the sensor is determined to be

[0061] Rx=(Rcal)(Ical / Ib1)(Ib2 / Ix),

[0062] where Ib1 is the current in the bridge resistor when the excitation is Vexc1, and Ib2 is the current in the bridge resistor when the excitation is Vexc2. Because the measurement excitation voltage and gain are the same for each pair of current measurements, the accuracy of the measurement voltage and gain in the measurement system is not important.

[0063] In an example intended to be illustrative and not limiting, if the sensor impedance is known to be in the range of approximately 200Ω and Rcal is 10kΩ, then the bridge resistance may be 1.128kΩ. In this case, the ratio of the bridge resistance to the calibration resistance and the ratio of the bridge resistance to the sensor impedance may not be very large, and a single bridge resistance value can be used. The measurement circuit can apply an excitation signal to the sensor to obtain an estimate of the impedance before setting the bridge resistance value. The measured value is an estimate because the excitation signal generally does not have the required accuracy. The measurement circuit 616 can set the bridge resistance value to a rough or approximate resistance value before more accurately determining the bridge resistance value. If desired, the measurement circuit 616 can also be used to measure the resistance of Rcal. The multiplexer circuit 630 can be used to apply the excitation signal to the calibration resistance, and the measurement circuit 616 can use the excitation signal to calculate the calibration resistance.

[0064] In another example, if the impedance difference between the sensor impedance Rx and the calibration resistor Rcal is too large, multiple bridge resistance steps may be used to bridge the measurement value between Rcal and Rx. For example, as described in the previous example, the measurement circuit 616 may apply the first excitation signal Vexc1 to the calibration and first bridge resistor Rb1 to measure the calibration current Ical and the first bridge current Ib. 11 , where Ib 11 Ib is the bridge current for the first bridge resistance value and the first excitation signal. The first bridge resistance value can be set to be closer to Rcal than Rx. The measurement circuit 616 applies the second excitation signal to the first bridge resistance value and measures the second bridge current Ib. 12 , where Ib 12 is the bridge current for the first bridge resistance Rb1 and the second excitation signal Vexc2.

[0065] The bridge resistance is then changed to a second value, Rb2, which is closer to Rx than Rcal. In an example intended to be illustrative and not limiting, if the sensor impedance is known to be in the range of approximately 200Ω and Rcal is 10kΩ, then the value of Rb1 can be set to 712Ω and Rb2 can be 2.53kΩ. A second excitation signal, Vexc2, is applied to the second bridge resistance, and a third bridge current, Ib, is measured. 22Apply the third excitation signal Vexc3 to the second bridge resistor Rb2 and measure the fourth bridge current Ib 23 , where Ib 23 is the bridge current for the second bridge resistance Rb2 and the third excitation signal Vexc3. Then, the third excitation signal is applied to the sensor impedance Rx, and the sensor current Ix is measured. Then, the calibration resistor Rcal, the calibration current Ical, the first bridge current Ib 11 , the second bridge current Ib 12 , the third bridge current Ib 22 , the fourth bridge current Ib 23 The impedance of the sensor Rx is determined by the following formula:

[0066] Rx=(Rcal)(Ical / Ib 11 )(Ib 12 / Ib 22 )(Ib 23 / Ix).

[0067] Figure 7 1 is a flow chart of an example method 700 for controlling a test circuit to measure the internal impedance of an electronic sensor. At 705, a first predetermined excitation signal is applied to a calibration resistor and a calibration current is measured. A bridge resistance value is then selected. In some examples, the test circuit determines an approximate or rough value of the sensor impedance, and the test circuit or a user sets the bridge resistance value accordingly. The test circuit may include a table stored in memory, and the test circuit may set the bridge resistance by using the approximate sensor impedance as an index into the table. At 710, the same first excitation signal is applied to the bridge resistor and a first bridge current is measured.

[0068] At 715, a second predetermined excitation signal is applied to the bridge resistor and a second bridge current is measured. At 720, a second excitation signal is applied to the sensor and the sensor current is measured. At 725, the internal impedance of the sensor is calculated by the test circuit using the calibration resistor, the calibration current, the first bridge current, the second bridge current, and the sensor current. The calculated internal impedance can then be provided to a user or a processing program. For example, the internal impedance can be used to estimate the remaining useful life of the electronic sensor.

[0069] More than one bridge resistor may be required. The bridge resistor can be determined based on a ratio. The test circuit can determine the bridge resistor to maintain a ratio of the calibration impedance to the bridge impedance of approximately 4. If the ratio of the selected bridge impedance to the approximate sensor value is not within the expected ratio range, the test circuit can select a second bridge resistor that is within the expected ratio range for the sensor and within the expected ratio range for the first bridge resistor value. The sensor impedance is then determined using the calibration resistor, calibration current, four bridge currents, and sensor current as in the previous example. This approach is scalable. If the difference between the calibration resistor and sensor impedance values ​​is too large, more than two bridge resistors may be required.

[0070] Figure 8 is a circuit diagram of a portion of another example of a test circuit 804 electrically coupled to a sensor circuit 806. In addition to addressing power consumption and circuit noise, circuits for monitoring electronic sensor outputs may need to tailor the output of the sensor circuit to improve accuracy.

[0071] The test circuit 804 may be included on an integrated circuit and includes inputs for receiving electrical signals from the sensor circuit 806, the DAC circuit 832, the PGA 834, and the measurement circuit 836. In some examples, the sensor circuit is included on the same integrated circuit and the test circuit. The sensor can be used to detect the concentration of a chemical or gas within an environment containing the sensor. The internal impedance of the sensor varies with the concentration. The sensor is coupled to a resistor divider including a reference resistor 840 (Rref). A switch 842 can enable the resistor divider during measurement of the sensor output. The switch can also be activated for a short time (e.g., 200 microseconds (200 μs)) to allow the current path through the sensor to briefly heat the sensor, and then deactivated to save power. By measuring Rref, the current can be monitored to accurately control the average power burned on the sensor, and the temperature can be accurately controlled to accurately control the sensitivity of the sensor to the measurement.

[0072] Measurement circuit 836 may include a controller to disconnect the switch when not performing measurements to conserve energy. The voltage Vcc applied to the sensor is divided by the internal impedance of sensor 806 and reference resistor 840. To monitor the sensor, the voltage of the signal from the sensor varies with the concentration of the chemical or gas. For example, the sensor may be a gas sensor. The internal impedance of the sensor may vary with the gas concentration, providing a voltage proportional to the gas concentration.

[0073] The signal from sensor circuit 806 includes a direct current (DC) offset and a varying signal component. A DC offset can occur when the internal impedance of the sensor circuit has a small, approximate impedance variation. For example, the internal impedance of a sensor can vary between 18Ω and 20Ω over a range of gas concentrations. The voltage generated by the 18Ω impedance will appear as a DC offset in the electrical signal from the sensor.

[0074] Figure 9 9 is a graph of an example of the output of the sensor circuit 806 as a function of gas concentration. The DC component is shown as Vshift. Graph 905 shows that the voltage output varies between 2.37 volts (2.37V) and 2.5V. If necessary, the DC offset prevents the use of a lower voltage measurement circuit and can limit the measurable range of output variation, which may affect measurement accuracy. To improve accuracy, the DC offset is removed. Graph 910 shows the sensor output after shifting the output to be centered around 0 volts and the signal gain applied to the signal from the sensor. Graph 910 shows that the accuracy of the measurement can be improved by a larger signal range, and a measurement circuit with a lower voltage can be used to monitor the output.

[0075] The test circuit 804 includes a DAC circuit 832 to remove DC offsets from signals received from the sensor. The DAC circuit 832 can be programmed by the user to subtract a known DC offset or automatically adjusted by the control circuit to subtract a measured DC offset. The PGA 834 applies signal gain to the signal shifted by the DAC circuit. The amount of gain provided by the PGA 834 can also be set by the user or automatically adjusted using the control circuit. The measurement circuit 836 generates a measurement of the varying signal component. In some embodiments, the measurement circuit 836 includes an analog-to-digital converter (ADC) circuit 838 for generating a digital value representing the signal from the sensor circuit 806. Figure 8 In the example shown, the ADC circuit is a 16-bit ADC circuit. The signal gain provided by the PGA allows for more signal swing, which makes the accuracy of the 16-bit ADC more useful. Depending on the application, the measurement circuit may also include a fast Fourier transform (FFT) circuit configured to measure the frequency response of varying signal components.

[0076] Figure 101 is a flow chart of an example of a method 1000 of controlling a test circuit to measure the internal impedance of an electronic sensor. At 1005, the test circuit receives an input signal from an electronic sensor. The input signal includes a DC offset component and a varying signal component. At 1010, the DC offset is removed from the input signal using a DAC circuit, and a signal gain is applied to the remaining varying signal component. At 1015, the varying signal component with the applied signal gain is measured using a measurement circuit. The measurement may include a digital value determined using an ADC circuit. The measurement may be provided to one or both of a user or a processing program. For example, the sensor may be an oxygen sensor. Figure 8 As shown in FIG, the test circuit may include a detection circuit 844. The detection circuit may generate an indication of a lower explosion limit (LEL) based on a measure of the varying signal component. The indication may be used to generate an alarm regarding the LEL.

[0077] The devices, methods, and systems described herein allow for monitoring smart sensors with low power consumption and improved accuracy.

[0078] Additional Notes

[0079] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The accompanying drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "examples." All publications, patents, and patent documents mentioned in this document are incorporated herein by reference in their entirety, as if individually incorporated by reference. In the event of a discrepancy between the usages of this document and a document incorporated herein by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable discrepancies, the usage in this document controls.

[0080] In this document, as is common in patent documents, the terms "a" or "an" are used to include one or more than one, independent of any other examples or usages of "at least one" or "one or more." In this document, unless otherwise indicated, the term "or" is used to refer to non-exclusivity, for example, "A or B" includes "A but not B," "B but not A," and "A and B." In the appended claims, the terms "including" and "in which" are used as the plain English equivalents of the respective terms "comprising" and "wherein." Moreover, in the following claims, the terms "including" and "comprising" are open-ended, that is, systems, devices, articles, or processes that include elements other than those listed after such terms in the claim are still considered to fall within the scope of the claim. Additionally, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels and are not intended to impose numerical requirements on their objects. The method examples described herein may be implemented, at least in part, by a machine or computer.

[0081] The above description is intended to be illustrative and not restrictive. For example, the above examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments may be used by those of ordinary skill in the art when viewing the above description. The provision of the abstract complies with 37 CFR § 1.72 (b) to enable the reader to quickly determine the nature of the technical disclosure. It should be understood at the time of submission that the abstract will not be used to interpret or limit the scope or meaning of the claims. Moreover, in the above specific embodiments, various features may be combined together to simplify the present disclosure. This should not be interpreted as an intention to indicate that the disclosed functions that are not claimed for protection are essential to any claim. On the contrary, the subject matter of the invention may be present in less than all the features of a particular disclosed embodiment. Therefore, the attached claims are hereby incorporated into the embodiments, with each claim independently serving as a separate embodiment. The scope of the present invention should be determined with reference to the attached claims together with the entire scope of equivalents authorized by these claims.

Claims

1. A test circuit, the test circuit comprising: an excitation circuit configured to apply an excitation signal to the electronic sensor, wherein the excitation circuit includes a configurable first circuit gain stage and a configurable second circuit gain stage, wherein in a first gain mode, the excitation circuit generates a first excitation signal from a test signal using a first signal gain applied by the first circuit gain stage and a second signal gain applied by the second circuit gain stage, and wherein in a second gain mode, the excitation circuit generates a second excitation signal from the test signal using a third signal gain applied by the first circuit gain stage and a fourth signal gain applied by the second circuit gain stage; as well as a measurement circuit configured to selectively initiate application of the first excitation signal or the second excitation signal to the electronic sensor and calculate an internal impedance of the electronic sensor; The measurement circuit is configured to start applying a first excitation signal to the electronic sensor when the internal impedance of the sensor has a first internal impedance range, and to start applying a second excitation signal to the electronic sensor when the internal impedance of the electronic sensor has a second internal impedance range, wherein the first internal impedance is greater than the second internal impedance range. 2 . The test circuit of claim 1 , wherein the signal gain of the second circuit gain stage is 1 in the first gain mode, and is less than 1 and greater than 0 in the second gain mode. 3 . The test circuit of claim 1 , wherein the signal gain of the first gain circuit stage is greater than 1 in the first gain mode, and is less than 1 and greater than 0 in the second gain mode. 4 . The test circuit of claim 1 , comprising a digital-to-analog converter circuit configured to generate the test signal. 5 . The test circuit of claim 4 , comprising a control circuit configured to control the digital-to-analog converter circuit to change one or both of the frequency of the test signal and the amplitude of the test signal.

6. The test circuit of claim 1 , wherein the measurement circuit is configured to: Determine the type code of the electronic sensor; and A signal gain of one or both of the first circuit gain stage and the second circuit gain stage is selected based on the determined type code.

7. A method of monitoring an electronic sensor using a test circuit, the method comprising: When the internal impedance of the electronic sensor has a first internal impedance range, applying a first excitation signal to the electronic sensor in a first gain mode; wherein in the first gain mode, the first excitation signal is generated from the test signal using a first signal gain generated using a first circuit gain stage and a second signal gain generated using a second circuit gain stage; applying a second excitation signal to the electronic sensor in a second gain mode when the internal impedance of the electronic sensor has a second internal impedance range, wherein the first internal impedance is greater than the second internal impedance range; wherein in the second gain mode, the second excitation signal is generated from the test signal using a third signal gain generated using the first circuit gain stage and a fourth signal gain generated using the second circuit gain stage; and calculating an internal impedance of the electronic sensor using the test circuit using a first excitation signal in a first gain mode and using a second excitation signal in a second gain mode; and Provides the calculated internal impedance to the user or process.

8. The method according to claim 7, wherein applying the first excitation signal comprises generating the first excitation signal using a signal gain of 1 in the second circuit gain stage; and Wherein applying the second excitation signal includes generating a second gain signal using a signal gain less than 1 and greater than 0 in a second circuit gain stage.

9. The method according to claim 7, wherein applying the first excitation signal comprises generating the first excitation signal using a signal gain greater than 1 in a first circuit gain stage; and Wherein applying the second excitation signal comprises generating the second excitation signal using a signal gain less than 1 and greater than 0 in the first circuit gain stage.

10. The method of claim 7, comprising generating the test signal using a digital-to-analog converter circuit.

11. The method of claim 10, comprising controlling the digital-to-analog converter circuit to vary one or both of the frequency of the test signal and the amplitude of the test signal.

12. The method of claim 7, wherein the signal gain of the first gain stage is changed from a first signal gain to a third signal gain by changing the gain of a programmable gain amplifier of the first circuit gain stage, and the signal gain of the second gain stage is changed from a second signal gain to a fourth signal gain by changing the resistance value of a circuit element of the second circuit gain stage.

13. An integrated circuit comprising: Sensor circuit; an excitation circuit configured to apply an excitation signal to the sensor circuit, wherein the excitation circuit includes a configurable first circuit gain stage and a configurable second circuit gain stage, wherein in a first gain mode, the excitation circuit generates a first excitation signal from a test signal using a first signal gain applied by the first circuit gain stage and a second signal gain applied by the second circuit gain stage, and wherein in a second gain mode, the excitation circuit generates a second excitation signal from the test signal using a third signal gain applied by the first circuit gain stage and a fourth signal gain applied by the second circuit gain stage; as well as a measurement circuit configured to selectively initiate application of a first excitation signal or a second excitation signal to the sensor circuit and calculate an internal impedance of the sensor circuit, apply a predetermined excitation signal to the sensor circuit, determine a range of the internal impedance of the sensor circuit, and select a signal gain of one or both of the first circuit gain stage and the second circuit gain stage based on the determined range of the internal impedance; as well as The measurement circuit is configured to start applying a first excitation signal to the sensor circuit when the internal impedance of the sensor circuit has a first internal impedance range, and to start applying a second excitation signal to the sensor circuit when the internal impedance of the sensor circuit has a second internal impedance range, wherein the first internal impedance is greater than the second internal impedance range.

14. The integrated circuit of claim 13, further comprising a digital-to-analog converter circuit configured to generate a test signal.

15. The integrated circuit of claim 14, comprising a control circuit configured to control the digital-to-analog converter circuit to vary one or both of a frequency of the test signal and an amplitude of the test signal.

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