Improving the precision of a non-amplified MEMS pressure sensor

Abstract

The invention discloses utilizing a four-thermistor circuit to improve the precision of a pressure sensing device. In a particular embodiment, a pressure sensor includes a pressure sensing element; two or more first thermistors electrically coupled to the pressure sensing element, the two or more first thermistors providing compensation for deviations of the pressure sensing element within a lower heat range; and two or more second thermistors electrically coupled to the pressure sensing element, the two or more second thermistors providing compensation for deviations of the pressure sensing element within a lower heat range.

Description

Background Art

[0001] In the aerospace industry, it is reported that more than 80% of piezoresistive micro-electromechanical system (MEMS) pressure sensors are configured with passive electronics (also called "unamplified") for their higher reliability and operating temperature range. In contrast to "amplified" sensors that use application specific integrated circuits (ASICs) (signal conditioners) to calibrate the unit and adjust the sensor output, unamplified sensors are calibrated using a series of resistors and thermistors (whose resistance changes with temperature). For amplified sensors, the ASIC can be programmed to thermally compensate for deviations of the piezoresistive micro-electromechanical system (MEMS) die from the rated output, while for passive circuits, the thermistor plays the role of thermal compensation. Summary of the invention

[0002] According to an embodiment of the present disclosure, a calibration mechanism for an unamplified MEMS pressure sensor using at least four thermistors is provided, wherein at least two of these thermistors are provided to compensate for thermal deviations of the MEMS die within a higher temperature range (e.g., at room temperature and thermal temperature), and at least two thermistors are provided to compensate for thermal deviations within a lower temperature range (e.g., low temperature). A passive circuit using one or two thermistors can thermally compensate for MEMS die deviations at room temperature and thermal temperature. However, at low temperatures (below -20°C), the sensor output error will increase. In some cases, the sensor error may be close to 4% of the full scale at -55°C. Compared to a one or two thermistor configuration, the four thermistor configuration according to the present disclosure provides higher reading accuracy, with significant accuracy improvements at low temperatures below -20°C.

[0003] One embodiment relates to a pressure sensor that utilizes a four-thermistor circuit to improve accuracy. The pressure sensor includes a pressure sensing element. The pressure sensor also includes two or more first thermistors electrically coupled to the pressure sensing element, the two or more first thermistors providing compensation for deviations of the pressure sensing element in a lower thermal range. The pressure sensor also includes two or more second thermistors electrically coupled to the pressure sensing element, the two or more second thermistors providing compensation for deviations of the pressure sensing element in an upper thermal range. In some examples, the pressure sensor is an amplified pressure sensor. In some examples, the pressure sensor is a piezoresistive pressure sensor.

[0004] In some examples, the two or more first thermistors have a resistance of 10Ω at room temperature and a beta (β) sensitivity coefficient of 3470. In some examples, the two or more second thermistors have a resistance of 500Ω at room temperature and a β sensitivity coefficient of 2941.

[0005] In some examples, the pressure sensing element is a microelectromechanical system (MEMS) die. The MEMS die can be mounted on a printed circuit board (PCB) assembly, and two or more first thermistors and two or more second thermistors are arranged on the PCB assembly. In some examples, the PCB assembly includes a first lower thermal range compensation stage, a second lower thermal range compensation stage, a first upper thermal range compensation stage, at least one zero offset adjustment stage, at least one zero offset thermal compensation stage, and at least one span adjustment stage, the first lower thermal range compensation stage includes one of the first thermistors and one or more linearization resistors, the second lower thermal range compensation stage includes one of the first thermistors and one or more linearization resistors, the first upper thermal range compensation stage includes one of the second thermistors and one or more linearization resistors, and the second upper thermal range compensation stage includes one of the second thermistors and one or more linearization resistors.

[0006] In some examples, the maximum error of the pressure sensing element is + / - 1.5% of full scale.In some examples, the lower thermal range includes 0 degrees Celsius to -55 degrees Celsius, and wherein the upper thermal range includes 85 degrees Celsius to 150 degrees Celsius.

[0007] Another embodiment relates to a method of manufacturing a pressure sensor using a four-thermistor circuit. The method includes coupling a first thermistor that compensates in a lower thermal range and a second thermistor that compensates in an upper thermal range in series to a first input of an unamplified microelectromechanical system (MEMS) pressure sensing die. The method also includes coupling a third thermistor that compensates in the lower thermal range and a fourth thermistor that compensates in the upper thermal range in series to a second input of the unamplified MEMS pressure sensing element. The method also includes coupling one or more outputs of the MEMS pressure sensing element to a connector configured to engage with an external device.

[0008] The foregoing and other objects, features and advantages of the present invention will become apparent from the following more particular description of exemplary embodiments of the present invention as illustrated in the accompanying drawings, wherein like reference numerals generally refer to like parts of exemplary embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A schematic diagram of an example pressure sensor utilizing a four-thermistor circuit to improve the accuracy of an unamplified MEMS pressure sensor is shown in accordance with some embodiments of the present disclosure.

[0010] Figure 2 A schematic diagram is shown of an example circuit utilizing a four-thermistor circuit to improve the accuracy of an unamplified MEMS pressure sensor according to some embodiments of the present disclosure.

[0011] Figure 3 A schematic diagram is shown of an example circuit utilizing a four-thermistor circuit to improve the accuracy of an unamplified MEMS pressure sensor according to some embodiments of the present disclosure.

[0012] Figure 4 A schematic diagram is shown of an example circuit utilizing a four-thermistor circuit to improve the accuracy of an unamplified MEMS pressure sensor according to some embodiments of the present disclosure.

[0013] Figure 5 A flow chart illustrating an example method for improving the accuracy of an unamplified MEMS pressure sensor using a four-thermistor circuit according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0014] Advantages and other features of the systems and methods disclosed herein will become more readily apparent to those skilled in the art from the following detailed description of certain embodiments taken in conjunction with the accompanying drawings that illustrate representative embodiments of the invention.

[0015] In the specification, common features in the drawings are represented by common reference numerals. As used herein, various terms are used only for the purpose of describing a specific implementation and are not intended to be limited. For example, the singular forms "a", "an" and "the" also include plural forms unless the context clearly states otherwise. It can be further understood that the terms "comprise", "comprises" and "comprising" can be used interchangeably with "include", "includes" or "including". In addition, it can be understood that the term "wherein" can be interchanged with the term "wherein". As used herein, "exemplary" can represent examples, implementations and / or aspects, and should not be interpreted as limiting or indicating preferences or preferred implementations. As used herein, ordinal numbers (such as "first", "second", "third", etc.) used to modify elements (such as structures, components, operations, etc.) do not themselves represent any priority or order of the element relative to another element, but only distinguish the element from another element with the same name (except for the use of ordinal numbers). As used herein, the term "set" refers to a grouping of one or more elements and the term "plurality" refers to a plurality of elements.

[0016] As used herein, "coupling" may include "communication coupling", "electrical coupling" or "physical coupling", and may also (or alternatively) include any combination thereof. Two devices (or components) may be directly or indirectly coupled (e.g., communication coupling, electrical coupling or physical coupling) through one or more other devices, components, wires, etc. As illustrative, non-limiting examples, two electrically coupled devices (or components) may be included in the same device or in different devices, and may be connected by electronic devices, one or more connectors or inductive coupling. In some implementations, two devices (or components) that are communicatively coupled (e.g., electrically communicating) may directly or indirectly send and receive electrical signals (digital signals or analog signals), such as through one or more wires, buses, networks, etc. As used herein, "direct coupling" may include two devices that are coupled (e.g., communication coupling, electrical coupling or physical coupling) without intermediate components.

[0017] Additionally, directional words, such as "up," "down," "inside," and "outside," are used only to help describe the position of parts relative to each other. For example, the "inside" surface of a part is used only to describe a surface that is separate from the "outside" surface of the same part. There are no directional words used to describe absolute directions (i.e., the "inside" part must always be inside a part).

[0018] Note that the techniques herein are well suited for use in any type of sensor application, such as the pressure sensor assembly described herein. However, it should be noted that the embodiments herein are not limited to use in these applications, and the techniques discussed herein are also well suited for other applications.

[0019] Figure 1 A schematic diagram of an example pressure sensor 100 is shown that utilizes a four-thermistor circuit to improve the accuracy of an unamplified MEMS pressure sensor in accordance with some embodiments of the present disclosure. The pressure sensor is configured for use in a variety of applications, such as aerospace applications. Figure 1 An exemplary pressure sensor of includes a connector 110, a housing 112, and a solid steel port body 114, which are coupled together and surround the other components of the pressure sensor 100. An opening in the port body 114 allows fluid to flow from the fluid medium into an internal passage 118 defined by the peripheral wall of the port body 114. In some examples, threads on the exterior of the port body 114 allow the port body 114 to be fixed to a structure (not shown) surrounding the fluid medium, keeping the internal passage 118 fluidly connected to the fluid medium. For example, the port body 114 can be threaded to be screwed into a structure surrounding the fluid medium. In other examples, the port body 114 can include a threaded cavity to receive a threaded member, or can be fixed by brazing or other techniques that occur to those skilled in the art.

[0020] The pressure sensor includes a pressure sensing element 130. In some examples, the pressure sensing element 130 is disposed within an inner cavity 132 defined by a peripheral wall of a port body 114 that is fluidly connected to an internal passage 118. In some examples, the pressure sensing element 130 is a micro-electromechanical system (MEMS) die that includes a diaphragm in contact with one or more piezoresistive strain gauges. Changes in the pressure of the fluid medium exert a force on the diaphragm that is measured by the strain gauge, which in turn generates an electrical signal representative of the pressure change, as is known in the art.

[0021] The pressure sensing element is electrically coupled to a printed circuit board (PCB) 142 or other electronic module assembly (EMA). In some examples, the seal between the port body 114 and the PCB 142 prevents the fluid medium from escaping from the inner cavity 132 in which the pressure sensing element 130 is arranged. In some examples, the pressure sensing element 130 is directly mounted to the PCB 142. Alternatively, the pressure sensing element 130 can be electrically coupled to the PCB 142 by wiring or ribbon. In some examples, the PCB 142 is disposed in an inner cavity 150 defined by the peripheral wall of the housing 112. The housing 112 can also enclose wiring, springs, or other electrical couplers that connect the PCB 142 to the monitoring device through the connector 110. The circuit on the PCB 142 receives the electrical signal from the strain gauge of the pressure sensing element 130 and provides a calibrated electrical output through one or more output ports of the connector 110.

[0022] In piezoresistive microelectromechanical system (MEMS) pressure sensors, the sensitivity of the sensor decreases with increasing temperature. For unamplified pressure sensors, passive components such as thermistors are used to provide thermal compensation to calibrate the pressure sensor. In particular, negative temperature coefficient (NTC) thermistors are used for thermal compensation. NTC thermistors are resistors with a negative temperature coefficient, which means that the resistance decreases as the temperature increases. Thermistors have high sensitivity because small changes in temperature result in large changes in resistance. In addition, the response of thermistors is not linear over the entire operating temperature range of the thermistor. That is, the change in resistance for a given temperature change is not constant over the temperature range of the thermistor. The thermistor response can be linearized by connecting a fixed resistor in parallel and / or in series with it.

[0023] To better understand the role of NTC thermistors in thermal compensation, it will be appreciated that NTC thermistors are characterized by having a number of manufacturer-specified operating parameters. One such parameter is resistance, which is the resistance of the thermistor at the manufacturer's specified temperature (usually 25°C). Another parameter is tolerance, which indicates how much the resistance can vary from the specified value, usually expressed as a percentage. For example, if a thermistor with a 10% tolerance has a specified resistance of 10,000 ohms at 25°C, the measured resistance at that temperature will range from 9,000 ohms to 11,000 ohms. Another parameter is the beta coefficient (also called the beta constant, beta sensitivity parameter, or simply beta). The beta coefficient is a value that represents the relationship between resistance and temperature over a specified temperature range. For example, "338025 / 50" means that over the temperature range of 25°C to 50°C, the beta constant is 3380. Often, the beta coefficient is simply specified as, for example, 3380 degrees Kelvin. Another parameter is the operating temperature range, which includes the minimum and maximum operating temperatures of the thermistor. Yet another parameter is the thermal time constant, which indicates the time required to reach 63% of the difference between the old and new temperatures. Yet another parameter is the heat dissipation constant, which is the amount of power required to raise the temperature of the thermistor by 1°C due to self-heating. Generally, power dissipation should be kept low to prevent self-heating. Yet another parameter is the maximum power dissipation to prevent damage to the thermistor. Other characteristics include the resistance-temperature table, which is a table of resistance values ​​and associated temperatures within the thermistor's operating temperature range as specified by the thermistor manufacturer.

[0024] When the pressure sensor is operated in the "hot" temperature range, an NTC thermistor can be provided on the input voltage of the MEMS sensing element to provide thermal compensation. As used herein, the "hot" temperature range can be approximately room temperature and above (e.g., approximately 25°C to approximately 150°C). NTC thermistors have been shown to effectively reduce the errors of pressure sensors in the hot temperature range. However, the pressure sensor may also experience significant errors in the "cold" temperature range. As used herein, the "cold" temperature range may be approximately freezing point and below (e.g., approximately 0°C to approximately -55°C). At -55°C, the percentage error over the full scale may reach 4%. In the cold temperature range, thermistors used for hot thermal compensation generally cannot provide adequate thermal compensation.

[0025] According to an embodiment of the present disclosure, the pressure sensor is equipped with a plurality of thermistors with different characteristics to provide both hot and cold thermal compensation. In some examples, the pressure sensor 100 includes one or more lower thermal range (or "cold") compensation thermistors and one or more upper thermal range (or "hot") compensation thermistors, one or more lower thermal range (or "cold") compensation thermistors are used to calibrate the output signal of the pressure sensing element 130 to compensate for thermal deviations under cold temperature conditions (e.g., below about 0°C), and one or more upper thermal range (or "hot") compensation thermistors are used to calibrate the output signal of the temperature sensing element 30 to compensate for thermal deviations under hot temperature conditions (e.g., above about 85°C). In some examples, the PCB 142 includes two or more cold temperature compensation thermistors and two or more hot temperature compensation thermistors.

[0026] To explain further, Figure 2 A block diagram of an example pressure sensor 200 utilizing a four-thermistor circuit to improve accuracy is presented in accordance with some embodiments of the present disclosure. Figure 2 Examples of passive components for compensating and adjusting the MEMS pressure sensing element 250 are provided. Figure 2 An example of includes a positive voltage input 202, which is fed to a lower thermal range compensation stage 204, or a "cold" compensation stage, for compensating for deviations of the MEMS pressure sensing element 250 at low temperatures. The lower thermal range compensation stage 204 includes one or more resistors and at least one lower thermal range compensation thermistor 206. The one or more resistors in the lower thermal range compensation stage 204 may also include a resistor for linearizing the output of the lower thermal range compensation thermistor 206, and may include one or more adjustable resistors. In some examples, the lower thermal range compensation thermistor 206 is an NTC thermistor with an impedance of 10Ω and a beta coefficient of 3470K. However, it should be understood that other values ​​of the lower thermal range compensation thermistor 206 may be selected based on the operating characteristics and operating conditions of the pressure sensor. For example, the input voltage, MEMS sensing element characteristics, target pressure range, and target temperature range may affect the selection of the value of the thermistor 206.

[0027] The output of the lower thermal range compensation stage 204 is fed to a span compensation stage 208. The span adjustment stage 208 includes one or more resistors for adjusting the span of the full-scale output of the MEMS pressure sensing element 250. In some examples, the span adjustment stage 208 includes an adjustable resistor.

[0028] The output of the span compensation stage 208 is fed to an upper thermal range compensation stage 210, or a "thermal" compensation stage, which compensates for the deviation of the MEMS pressure sensing element 250 when the ambient conditions are within an upper thermal range relative to the lower thermal range (e.g., 85°C to 150°C). The upper thermal range compensation stage 210 includes one or more resistors and at least one upper thermal range compensation thermistor 212. The upper thermal range compensation stage 210 may also include other resistors for linearizing the output of the upper thermal range compensation thermistor 212, which may include one or more adjustable resistors. In some examples, the upper thermal range compensation thermistor 212 is an NTC thermistor with an impedance of 500Ω and a beta coefficient of 2941K. NTC thermistors with such values ​​are common. However, it should be understood that other values ​​of the upper thermal range compensation thermistor 212 may be selected based on the operating characteristics and operating conditions of the pressure sensor. For example, as will be appreciated by those skilled in the art, input voltage, MEMS sensing element characteristics, target pressure range, and target temperature range may influence the selection of the value of the upper thermal range compensation thermistor 212 .

[0029] The output of the upper thermal range compensation stage 210 is fed to a first zero-offset thermal compensation stage 214 and a second zero-offset thermal compensation stage 242 connected in parallel with the MEMS pressure sensing element 250. The zero-offset thermal compensation stages 214, 242 each include one or more resistors that are used to compensate for the thermal sensitivity of the offset voltage of the MEMS pressure sensing die 250. The zero-offset thermal compensation stages 214, 242 may include adjustable resistors.

[0030] The positive output terminal 216 is connected in parallel to the output of the zero offset thermal compensation stage 214 and the positive output of the MEMS pressure sensing element 250. The negative output terminal 236 is connected in parallel to the output of the zero offset thermal compensation stage 242 and the negative output of the MEMS pressure sensing element 250.

[0031] Figure 2The example also includes a negative input 218 fed to a lower thermal range compensation stage 224 (or "cold" compensation stage), which is used to compensate for the deviation of the MEMS pressure sensing element 250 at low temperatures (e.g., below 0°C). The lower thermal range compensation stage 224 includes one or more resistors and at least one lower thermal range compensation thermistor 226. The lower thermal range compensation stage 224 may also include a resistor for linearizing the output of the lower thermal range compensation thermistor 226, and may include one or more adjustable resistors. In some examples, the lower thermal range compensation thermistor 226 is an NTC thermistor with an impedance of 10Ω and a beta coefficient of 3470K. NTC thermistors with such values ​​are common. However, it should be understood that other values ​​of the lower thermal range compensation thermistor 226 can be selected based on the operating characteristics and operating conditions of the pressure sensor. For example, input voltage, MEMS sensing element characteristics, target pressure range, and target temperature range may influence the selection of the value of thermistor 226 , as will be appreciated by one skilled in the art.

[0032] The output of the lower thermal range compensation stage 224 is fed to a span adjustment stage 228. The span adjustment stage 228 includes one or more resistors for adjusting the span of the full-scale output of the MEMS pressure sensing element 250. In some examples, the span adjustment stage 228 includes an adjustable resistor.

[0033] The output of the span compensation stage 228 is fed to the upper thermal range compensation stage 230, or "thermal" compensation stage, for compensating for the deviation of the MEMS pressure sensing element 250 in the upper thermal range. The upper thermal range compensation stage 230 includes one or more resistors and at least one upper thermal range compensation thermistor 232. The upper thermal range compensation stage 230 may also include other resistors for linearizing the output of the upper thermal range compensation thermistor 232, which may include one or more adjustable resistors. In some examples, the upper thermal range compensation thermistor 232 is an NTC thermistor with an impedance of 500Ω and a beta coefficient of 2941K. NTC thermistors with such values ​​are common. However, it should be understood that other values ​​of the upper thermal range compensation thermistor 232 can be selected based on the operating characteristics and operating conditions of the pressure sensor. For example, as will be understood by those skilled in the art, the input voltage, MEMS sensing element characteristics, target pressure range, and target temperature range can affect the selection of the value of the upper thermal range compensation thermistor 232.

[0034] The output of the upper thermal range compensation stage 230 is fed to the zero offset adjustment stage 240. When no pressure is applied, the MEMS pressure sensing element 250 outputs an offset voltage. One or more resistors (which may include an adjustable resistor) in the zero offset adjustment stage 240 calibrate the offset voltage. The output of the zero offset adjustment stage 240 is provided to the MEMS pressure sensing element 250 as a negative input.

[0035] To explain further, Figure 3 A schematic diagram of an example circuit 300 for improving the accuracy of an unamplified MEMS pressure sensor using a four-thermistor circuit according to some embodiments of the present disclosure is shown. The example circuit 300 includes a pressure sensor element 302 as a MEMS pressure sensing die. For cold temperature calibration, a first voltage input (e.g., a positive input in this example) to the pressure sensor element 302 is calibrated by a first cold compensation thermistor network 312. The first cold compensation thermistor network 312 includes a resistor network including a first cold compensation thermistor 314 (labeled "RT3") and other resistors R21, R22, R23 for linearization. In one example, the first cold compensation thermistor 314 is an NTC thermistor with a resistance of 10Ω at room temperature. In such an example, the beta coefficient of the thermistor 314 can be 3470. As will be appreciated by one of ordinary skill in the art, the values ​​of the other resistors R21, R22, R23 can be selected according to the desired circuit characteristics of a particular application. For room temperature and / or thermal temperature calibration, the first voltage input is further calibrated by a first thermal compensation thermistor network 304. The first thermal compensation thermistor network 304 includes a resistor network including a first thermal compensation thermistor 306 (labeled "RT2") and other resistors R14, R15, R16 for linearization. In one example, the first thermal compensation thermistor 306 is an NTC thermistor with a resistance of 500Ω at room temperature. In such an example, the beta coefficient of the thermistor 306 can be 2941. As will be appreciated by one of ordinary skill in the art, the values ​​of the other resistors R14, R15, R16 can be selected based on the desired circuit characteristics of a particular application. The example circuit 300 also includes a span adjustment network 330, which includes one or more resistors (labeled R18, R19) coupling the first cold compensation thermistor network 312 and the first thermal compensation thermistor network 304. The example circuit 300 also includes one or more zero offset adjustment resistor networks 322 , 324 including one or more resistors (eg, labeled R10 , R11 , R12 , R13 ) for zero offset adjustment.

[0036] For cold temperature calibration, one or more second voltage inputs (e.g., negative inputs in this example) to the pressure sensor element 302 are calibrated by a second cold compensation thermistor network 316. The second cold compensation thermistor network 316 includes a resistor network that includes a second cold compensation thermistor 320 (labeled "RT3") and other resistors R21, R22, R23 for linearization. In one example, the second cold compensation thermistor 320 is an NTC thermistor with a resistance of 10Ω at room temperature. In such an example, the beta coefficient of thermistor 320 can be 3470. As will be appreciated by one of ordinary skill in the art, the values ​​of the other resistors R21, R22, R23 can be selected based on the desired circuit characteristics of a particular application. For hot temperature calibration, the first voltage input is further calibrated by the second hot compensation thermistor network 308. The second thermal compensation thermistor network 308 includes a resistor network including a second thermal compensation thermistor 310 (labeled "RT1") and other resistors R3, R4, R5 for linearization. In one example, the second thermal compensation thermistor 310 is an NTC thermistor with a resistance of 500Ω at room temperature. In such an example, the beta coefficient of the thermistor 310 can be 3941. As will be appreciated by one of ordinary skill in the art, the values ​​of the other resistors R3, R4, R5 can be selected based on the desired circuit characteristics of a particular application. The example circuit 300 also includes a span adjustment network 328, which includes one or more resistors (labeled R1, R2) coupling the second cold compensation thermistor network 316 and the second thermal compensation thermistor network 308. The example circuit 300 also includes one or more zero-offset resistor networks 332 including one or more resistors (eg, labeled R6 , R7 , R8 , R9 ) for zero-offset thermal compensation or adjustment.

[0037] To explain further, Figure 4A schematic diagram of an example circuit 400 for improving the accuracy of an unamplified MEMS pressure sensor using a four-thermistor circuit according to some embodiments of the present disclosure is shown. The example circuit 400 includes a pressure sensor element 402 as a MEMS pressure sensing die. For cold temperature calibration, a first voltage input (e.g., a positive input in this example) to the pressure sensor element 402 is calibrated by a first cold compensation thermistor network 412. The first cold compensation thermistor network 412 includes a resistor network that includes a first cold compensation thermal resistor 414 (labeled "RT3") and one or more adjustable resistors RV9 for linearization. In one example, the first cold compensation thermistor 414 is an NTC thermistor with a resistance of 10Ω at room temperature. In such an example, the beta coefficient of the thermistor 414 can be 3470. For room temperature and / or hot temperature calibration, the first voltage input is further calibrated by the first hot compensation thermistor network 404. The first thermal compensation thermistor network 404 includes a resistor network including a first thermal compensation thermistor 406 (labeled "RT2") and one or more adjustable resistors RV1, RV2 for linearization. In one example, the first thermal compensation thermistor 406 is an NTC thermistor having a resistance of 500Ω at room temperature. In such an example, the beta coefficient of the thermistor 406 can be 2941. The example circuit 400 also includes a span adjustment network 430, which includes one or more adjustable resistors RV3 coupling the first cold compensation thermistor network 412 and the first thermal compensation thermistor network 404. The example circuit 400 also includes one or more zero offset thermal compensation resistor networks 422, 424, which include one or more resistors (e.g., labeled R11, R12) for zero offset thermal compensation.

[0038] For cold temperature calibration, one or more second voltage inputs (e.g., negative inputs in this example) to the pressure sensor element 402 are calibrated by a second cold compensation thermistor network 416. The second cold compensation thermistor network 416 includes a resistor network that includes a second cold compensation thermistor 420 (labeled "RT3") and one or more other adjustable resistors RV9 for linearization. In one example, the second cold compensation thermistor 420 is an NTC thermistor with a resistance of 10Ω at room temperature. In such an example, the beta sensitivity coefficient of thermistor 420 can be 3470. For room temperature and / or hot temperature calibration, the first voltage input is further calibrated by a second thermal compensation thermistor network 408. The second thermal compensation thermistor network 408 includes a resistor network that includes a second thermal compensation thermistor 410 (labeled "RT1") and one or more adjustable resistors RV7, RV8 for linearization. In one example, the second thermal compensation thermistor 410 is an NTC thermistor having a resistance of 500Ω at room temperature. In such an example, the beta coefficient of the thermistor 410 can be 2941. The example circuit 400 also includes a span adjustment network 428, which includes one or more adjustable resistors RV4 coupling the second cold compensation thermistor network 416 and the second thermal compensation thermistor network 408. The example circuit 400 also includes one or more zero offset adjustment networks 432, and the one or more zero offset adjustment networks 432 include one or more resistors RV5, RV6 for zero offset adjustment.

[0039] The improved circuit design according to the present disclosure, in which four thermistors are used, demonstrates an improvement in overall accuracy, especially at low temperatures. Test results for low pressure / high pressure sensors from 25 pounds per square inch (PSI) to 5000 PSI show that over a wide temperature range, such as from -55°C to +150°C, accuracy is improved by reducing the error to ±1.5% of full scale.

[0040] To explain further, Figure 5 A flow chart is presented of an example method for improving the accuracy of an unamplified MEMS pressure sensor using a four-thermistor circuit according to some embodiments of the present disclosure. Figure 5The method includes coupling 502 in series a first thermistor that compensates in a lower thermal range and a second thermistor that compensates in an upper thermal range to a first input of a non-amplified MEMS pressure sensing element. In some examples, coupling 502 the first thermistor and the second thermistor in series to the first input of the MEMS pressure sensing element can be performed by attaching a MEMS pressure sensing die to a printed circuit board (PCB), attaching a first thermistor to the PCB, attaching a second thermistor to the PCB, and providing a signal path that connects the first thermistor and the second thermistor in series to a positive input of the MEMS pressure sensing element. In a specific example, coupling 502 the first thermistor and the second thermistor in series to the first input of the MEMS pressure sensing element can be performed by, for example, implementing one of the above-described circuits on a PCB.

[0041] Figure 5 The method also includes coupling 504 in series a third thermistor for compensating in the lower thermal range and a fourth thermistor for compensating in the upper thermal range to a second input of the non-amplified MEMS pressure sensing element. In some examples, coupling 504 in series the third and fourth thermistors to the second input of the MEMS pressure sensing element can be implemented by attaching the third thermistor to a PCB, attaching the fourth thermistor to a PCB, and providing a signal path that connects the third and fourth thermistors in series to the negative input of the MEMS pressure sensing element. In a specific example, coupling 504 in series the third and fourth thermistors to the second input of the MEMS pressure sensing element can be performed by, for example, implementing one of the above circuits on a PCB.

[0042] Figure 5 The method also includes coupling 506 one or more outputs of the MEMS pressure sensing element to a connector configured to interface with an external device. In some examples, coupling 506 the one or more outputs of the MEMS pressure sensing element to the connector is performed by connecting a positive output of the MEMS pressure sensing element to a positive output terminal and connecting a negative output of the MEMS pressure sensing element to a negative output terminal on a PCB, and electrically connecting the positive output terminal and the negative output terminal to a connector to couple with an external device that measures a difference between the positive and negative outputs.

[0043] In view of the foregoing, it can be appreciated that a pressure sensor including two or more thermistors for lower thermal range compensation and two or more thermistors for upper thermal range compensation can reduce errors, improve the reliability of pressure sensor measurements, and expand the temperature conditions under which the pressure sensor can be reliably operated.

[0044] It can be understood from the above description that the various embodiments of the present invention may be modified and changed without departing from the true spirit of the present invention. The description in this specification is for illustrative purposes only and should not be interpreted as limiting. The scope of the present invention is limited only by the language of the appended claims.

Claims

1. A pressure sensor using a four-thermistor circuit to improve accuracy, the pressure sensor comprising: Pressure sensing element; two or more first thermistors electrically coupled to the pressure sensing element, the two or more first thermistors providing compensation for deviations of the pressure sensing element in a lower thermal range; as well as Two or more second thermistors are electrically coupled to the pressure sensing element, the two or more second thermistors providing compensation for deviations of the pressure sensing element in an upper thermal range.

2. The pressure sensor according to claim 1, wherein: The maximum error of the pressure sensing element is + / -1.5% of full scale.

3. The pressure sensor according to claim 1, wherein: The lower heat range includes 0 degrees Celsius to -55 degrees Celsius, and wherein the upper heat range includes 85 degrees Celsius to 150 degrees Celsius.

4. The pressure sensor according to claim 1, wherein: The two or more first thermistors have a resistance of 10Ω at room temperature.

5. The pressure sensor according to claim 1, wherein: The β sensitivity coefficient of the two or more first thermistors is 3470.

6. The pressure sensor according to claim 1, wherein: The two or more second thermistors have a resistance of 500Ω at room temperature.

7. The pressure sensor according to claim 1, wherein: The β sensitivity coefficient of the two or more second thermistors is 2941.

8. The pressure sensor according to claim 1, wherein: The pressure sensing element is a micro-electromechanical system (MEMS) die.

9. The pressure sensor according to claim 8, wherein: The MEMS die is mounted on a printed circuit board (PCB) assembly; and wherein the two or more first thermistors and the two or more second thermistors are arranged on the PCB assembly.

10. The pressure sensor according to claim 9, wherein: The PCB assembly comprises: a first lower thermal range compensation stage including one of said first thermistors and one or more linearization resistors; a second lower thermal range compensation stage including one of said first thermistors and one or more linearizing resistors; a first upper thermal range compensation stage including one of said second thermistors and one or more linearization resistors; a second upper thermal range compensation stage including one of said second thermistors and one or more linearizing resistors; at least one zero offset adjustment stage; at least one zero-offset thermal compensation stage; and At least one span adjustment stage.

11. The pressure sensor according to claim 1, wherein: The pressure sensor is an unamplified pressure sensor.

12. The pressure sensor according to claim 1, wherein: The pressure sensor is a piezoresistive pressure sensor.

13. A method of a pressure sensor utilizing a four-thermistor circuit, the method comprising: coupling a first thermistor for compensating in a lower thermal range and a second thermistor for compensating in an upper thermal range in series to a first input of an unamplified microelectromechanical system (MEMS) pressure sensing die; coupling in series a third thermistor for compensating in the lower thermal range and a fourth thermistor for compensating in the upper thermal range to a second input of the unamplified MEMS pressure sensing element; as well as One or more outputs of the MEMS pressure sensing element are coupled to a connector configured to interface with an external device.

14. The method according to claim 13, wherein: The maximum error of the MEMS pressure sensing element is + / -1.5% of the full scale.

15. The method according to claim 13, wherein: The lower heat range includes 0 degrees Celsius to -55 degrees Celsius, and wherein the upper heat range includes 85 degrees Celsius to 150 degrees Celsius.

16. The method according to claim 13, wherein: The two or more first thermistors have a resistance of 10Ω at room temperature.

17. The method according to claim 13, wherein: The β sensitivity coefficient of the two or more first thermistors is 3470.

18. The method according to claim 13, wherein: The two or more second thermistors have a resistance of 500Ω at room temperature.

19. The method according to claim 13, wherein: The β sensitivity coefficient of the two or more second thermistors is 2941.

20. The method according to claim 13, wherein: The pressure sensor is a piezoresistive pressure sensor.

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