Temperature compensation circuit of piezoresistive pressure sensor and piezoresistive pressure sensor

Abstract

The utility model relates to a temperature compensation circuit of a piezoresistive pressure sensor and the piezoresistive pressure sensor, a Wheatstone bridge adopts a constant voltage power supply mode, and the power supply current of the Wheatstone bridge is sampled as a positive feedback signal to compensate the temperature drift of the pressure sensor. The output voltage of the instrument amplifier returns to zero through the zeroing unit when the measured pressure is zero, and the output voltage (unit is millivolt) of the instrument amplifier is just the pressure value (unit is kilopascal) detected by the pressure sensor through the gain resistor, so that the direct reading of the pressure detected by the sensor is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of pressure sensors, in particular to a temperature compensation circuit of a piezoresistive pressure sensor and the piezoresistive pressure sensor. Background Art

[0002] High-temperature MEMS piezoresistive pressure sensors can operate over a wide temperature range, from -55°C to over 250°C. The natural frequency of these leadless MEMS piezoresistive pressure sensors is greater than 200kHz, ensuring high frequency response. MEMS piezoresistive pressure sensors typically incorporate a Wheatstone bridge circuit. Because the resistors in the Wheatstone bridge are made of silicon semiconductor material, their physical properties change with temperature. This causes the zero position and sensitivity of the MEMS pressure sensor's output signal to drift at different temperatures, referred to as temperature drift. The simplest way to address temperature drift in these MEMS piezoresistive pressure sensors is to connect resistors in series and parallel with the Wheatstone bridge to achieve temperature compensation and sensitivity adjustment. This method, while subject to high temperature compensation variability, is simple and widely used in applications where accuracy requirements are low. Another approach often uses Texas Instruments' PGA309 series chips for signal processing, reading calibration data from an external EEPROM for temperature compensation and pressure curve correction. This approach offers advantages such as low error and pressure curve correction, but is complex to debug and has a narrow bandwidth due to multiple amplification stages. Patent CN102252788A proposes using a negative temperature coefficient (NTC) thermistor (NTC) to offset the temperature drift caused by the increase in resistance of the silicon resistor strip in a MEMS pressure sensor over temperature. However, the major drawback of this method is that the NTC thermistor exhibits a nonlinear temperature dependence. Because the diffused silicon resistor strips made from MEMS have excellent linearity with temperature, using the nonlinear negative temperature dependence of the NTC thermistor to offset the highly linear positive temperature dependence of the MEMS pressure sensor resistor strips is difficult to achieve within an acceptable range. Other approaches include diode-based temperature control circuits, but most of these methods result in a narrower operating temperature threshold. Utility Model Content

[0003] The purpose of the utility model is to provide a temperature compensation circuit of a piezoresistive pressure sensor and a piezoresistive pressure sensor, which dynamically performs temperature compensation when measuring pressure at different temperatures, so that the output voltage-measured pressure line diagram of the pressure sensor at different temperatures tends to be consistent.

[0004] To achieve the above-mentioned objectives, the present utility model discloses a temperature compensation circuit for a piezoresistive pressure sensor, which includes a temperature compensation resistor Rs, an amplifying element, and a zero adjustment unit. The input end of the Wheatstone bridge of the piezoresistive pressure sensor is connected to a constant voltage power supply via the temperature compensation resistor Rs, and the output end of the Wheatstone bridge of the piezoresistive pressure sensor is connected to the input end of the amplifying element; the zero adjustment unit samples the power supply current of the Wheatstone bridge and converts it into a voltage, which is output to the zero adjustment end of the amplifying unit; the temperature compensation resistor Rs is a fixed-value resistor.

[0005] With the above settings, when the Wheatstone bridge resistor changes due to temperature, as illustrated by the example of an increase in the Wheatstone bridge resistor caused by temperature rise, the current flowing through the Wheatstone bridge resistor and the Wheatstone bridge decreases. Since the Wheatstone bridge is powered by a constant voltage and the temperature compensation resistor Rs is a fixed resistor, the voltage across the Wheatstone bridge decreases. Since the temperature compensation resistor Rs and the Wheatstone bridge are in series, the voltage across the temperature compensation resistor Rs decreases. Consequently, the voltage across the Wheatstone bridge increases, and the voltage at the input of the amplifier increases, which in turn increases the voltage at the output of the amplifier, thereby achieving temperature compensation. Simultaneously, the zeroing unit samples the Wheatstone bridge supply current and converts it into a voltage, which is output to the zeroing terminal of the amplifier, dynamically returning the output of the amplifier to zero (so that when the measured pressure is zero, the voltage output of the amplifier returns to zero). Through the above settings, temperature compensation can be actively performed according to the change in the resistance of the Wheatstone bridge due to temperature, and the slope and zero point of the output voltage-measured pressure line graph of the pressure sensor can be adjusted, so that the output voltage-measured pressure line graph of the pressure sensor at different temperatures tends to be consistent (the output voltage-measured pressure line graph under constant temperature conditions tends to be consistent with the standard temperature).

[0006] Preferably, the amplifying element is an instrumentation amplifier U1.

[0007] Preferably, the zero adjustment unit includes a sampling resistor R8, an operational amplifier U4 and a zero adjustment voltage source V adj The sampling resistor R8 is connected in series to the front end of the constant voltage power supply, the non-inverting input end of the operational amplifier U4 is connected to the connection between the sampling resistor R8 and the constant voltage power supply, and the zero voltage source V adj The inverting input terminal of the operational amplifier U4 is connected, and the output terminal of the operational amplifier U4 is connected to the zero adjustment terminal of the amplifying element; the zero adjustment voltage source V adj The sampling resistor R8 is set at the front end of the constant voltage power supply to sample the power supply current of the Wheatstone bridge, which will cause less interference to the Wheatstone bridge and ensure the detection accuracy. Vadj The voltage is adapted to the instrument amplifier U1, and the sampling voltage is matched to the zero voltage source VadjThe voltage difference is amplified by operational amplifier U4. The sampled voltage changes with the temperature of the Wheatstone bridge. Therefore, the voltage output by operational amplifier U4 to the zero-adjust terminal of instrumentation amplifier U1 also changes dynamically, thus achieving dynamic zero adjustment. In addition, this zero-adjust unit has a simple structure, which helps reduce the difficulty and cost of temperature compensation circuit board manufacturing.

[0008] Preferably, a voltage stabilizing chip U3 is further included, the output end of the voltage stabilizing chip U3 being the constant voltage power supply, and the sampling resistor R8 being connected in series with the input end of the voltage stabilizing chip U3. By providing the voltage stabilizing chip U3, a constant voltage power supply of the Wheatstone bridge can be ensured, thereby ensuring the reliability of temperature compensation.

[0009] Preferably, a gain resistor R is also included G , the gain resistor R G is a fixed value resistor, the gain resistor R G Connect one end of the instrumentation amplifier U1 to R G - pin, the gain resistor R G The other end of the instrumentation amplifier U1 is connected to the R G + pin. By setting the gain resistor R G The sensitivity or gain of the output voltage of the instrumentation amplifier U1 is adjusted so that the output voltage (mV) of the instrumentation amplifier U1 is consistent with the measured pressure value (kPa) of the pressure sensor, thereby achieving direct reading of the measured pressure value.

[0010] Preferably, the bandwidth of the instrumentation amplifier U1 is no less than 0.1 MHz. The output voltage of the Wheatstone bridge is amplified only once by the instrumentation amplifier U1. Using an instrumentation amplifier U1 with a large bandwidth ensures that the pressure sensor has a large bandwidth. Setting the bandwidth of the instrumentation amplifier U1 to no less than 0.1 MHz ensures that the leadless packaged pressure sensor achieves a high frequency response.

[0011] The utility model also discloses a piezoresistive pressure sensor adopting the temperature compensation circuit.

[0012] Preferably, the piezoresistive pressure sensor includes a sensor body, a connecting cable, and a compensation module. A Wheatstone bridge circuit is provided on the sensor body, and the temperature compensation resistor Rs, amplifier element, and zero adjustment unit are provided on the compensation module. The constant voltage power supply, temperature compensation resistor Rs, and amplifier element are connected to the Wheatstone bridge circuit via a connecting cable. With this configuration, the sensor body only needs to be placed in the measured environment, and the temperature compensation circuit can be placed in a normal temperature environment, thereby ensuring the accuracy of temperature compensation and the reliability of pressure detection.

[0013] Preferably, the connecting cable is a high-temperature resistant cable. The connecting cable is a high-temperature resistant cable to ensure the reliability and safety of the connection between the temperature compensation circuit and the Wheatstone bridge.

[0014] Preferably, the length of the connecting cable is not less than 0.5 m. This configuration ensures that the temperature compensation circuit is not affected by the temperature of the test environment.

[0015] The utility model has the following beneficial effects:

[0016] 1. This utility model employs a constant voltage power supply method and utilizes the Wheatstone bridge current as a feedback signal. When the Wheatstone bridge resistance changes with temperature, the output voltage of the amplifier element can be dynamically adjusted, thus providing active temperature compensation. Simultaneously, a zeroing unit samples the Wheatstone bridge supply current, converts it into an amplified voltage, and outputs it to the zeroing terminal of the amplifier element. This ensures that when the measured pressure reaches zero, the output voltage of the pressure sensor returns to zero. This arrangement ensures that the output voltage-measured pressure graph of the pressure sensor approaches a consistent value under different temperature conditions (approaching the output voltage-measured pressure graph under constant temperature conditions at a standard temperature), thereby simplifying the processing of the pressure sensor's output voltage.

[0017] 2. The output voltage of the pressure sensor is only amplified by one stage (instrumentation amplifier), so the bandwidth of the pressure sensor is less limited and can have a large bandwidth.

[0018] 3. Because the output voltage-measured pressure line graph of the pressure sensor tends to be consistent under different temperature conditions (the output voltage-measured pressure line graph under constant temperature conditions tends to be close to the standard temperature), by setting the gain resistor, the output voltage value (mV) of the pressure sensor and the measured pressure value (kPa) of the pressure sensor can be made consistent, realizing direct reading of the measured pressure value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the present utility model.

[0020] Figure 2 This is a circuit diagram of the utility model.

[0021] Description of main components symbols:

[0022] Sensor body 10, Wheatstone bridge 11;

[0023] Connecting cable 21, ordinary cable 22;

[0024] Compensation module 30. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] like Figure 1-2 As shown, this embodiment discloses a MEMS piezoresistive pressure sensor, which includes a sensor body 10, a connecting cable 21 and a compensation module 30. The sensor body 10 is used to detect pressure and is provided with a MEMS chip. A Wheatstone bridge 11 (composed of R1 / R2 / R3 / R4) is provided on the MEMS chip.

[0027] The compensation module 30 is equipped with a temperature compensation circuit to compensate for temperature drift caused by temperature-induced resistance changes in the Wheatstone bridge 11, ensuring that the pressure sensor can reliably and accurately output measured pressure values ​​even at different temperatures. The temperature compensation circuit is connected to the Wheatstone bridge 11 via a connecting cable 21. The compensation module 30 is also connected to an external power supply and output voltage signal (i.e., the voltage signal of the measured pressure) via a conventional cable 22. Because the sensor body 10 may be subjected to varying testing environments, such as high temperatures, to ensure reliable connection between the temperature compensation circuit and the Wheatstone bridge 11 and to reduce temperature interference on the temperature compensation circuit, in this embodiment, the connecting cable 21 is preferably a high-temperature-resistant cable, such as a PTFE Teflon cable, a mica fiberglass cable, a polyimide cable, or an MI metal-armored heating cable. Furthermore, the length of the connecting cable 21 is required to be no less than 0.5m.

[0028] The temperature compensation circuit includes a temperature compensation resistor Rs, a power supply unit, an amplifier element and a zero adjustment unit. The power supply unit includes two voltage regulator chips, namely, a voltage regulator chip U2, a voltage regulator chip U3 and a negative voltage charge pump U5. The IN end of the voltage regulator chip U2 is connected to the external power supply VDC through a common cable 22, and the GND end of the voltage regulator chip U2 is connected to the external ground wire through a common cable 22. The OUT end of the voltage regulator chip U2 directly powers the amplifier element (that is, connected to the V CC Pin), on the other hand, it is connected to the IN terminal of the voltage stabilizing chip U3 via the sampling resistor R8, the GND terminal of the voltage stabilizing chip U3 is grounded, and the OUT terminal of the voltage stabilizing chip U3 is a constant voltage power supply, which supplies power to the Wheatstone bridge 11. In this embodiment, the OUT terminal of the voltage stabilizing chip U3 is connected to the positive input terminal of the Wheatstone bridge 11 via the temperature compensation resistor Rs, and the negative input terminal of the Wheatstone bridge 11 is grounded.

[0029] In this case, the amplifier element is the instrumentation amplifier U1, whose input terminals (IN- and IN+) are connected to the output terminals of the Wheatstone bridge 11. The IN terminal of the negative charge pump U5 is connected to the OUT terminal of the voltage regulator chip U2, and the OUT terminal of the negative charge pump U5 is connected to the V EEThe output voltage of the OUT terminal of the voltage regulator chip U2 is +NV, and the output voltage of the OUT terminal of the negative charge pump U5 is -NV. The value of N is adapted to the instrumentation amplifier U1. G + Feet and R G - Connect a gain resistor R between the pins G The OUT pin of the instrumentation amplifier U1 is a voltage output terminal, which is connected to an external display component or other voltage signal receiving component through a common cable 22.

[0030] The REF pin of the instrumentation amplifier U1 is connected to the output of the zero adjustment unit. The zero adjustment unit samples the supply current of the Wheatstone bridge 11 and converts it into a voltage and outputs it to the zero adjustment terminal (i.e., the REF pin) of the instrumentation amplifier U1, so that the output voltage of the instrumentation amplifier U1 is returned to zero when the measured pressure is zero. Specifically, the zero adjustment unit includes a sampling resistor R8, an operational amplifier U4, and a zero adjustment voltage source V adj The non-inverting input of the operational amplifier U4 is connected to the connection between the sampling resistor R8 and the IN pin of the voltage regulator chip U3, and the zero voltage source V adj Connect to the inverting input of the operational amplifier U4, and the output of the operational amplifier U4 is connected to the zero adjustment terminal of the instrumentation amplifier U1. adj Output constant voltage, zero voltage source V adj This can be obtained by connecting voltage divider resistors R9 and R10 to the output end of the voltage regulator chip U2, and its voltage is adapted to the instrumentation amplifier U1.

[0031] In this case, the sampling resistor R8, the temperature compensation resistor Rs and the gain resistor R G They are all fixed resistors. When the resistance value of the Wheatstone bridge 11 changes due to temperature, the example of the increase in the resistance value of the Wheatstone bridge 11 caused by temperature increase is used for explanation. Because the Wheatstone bridge 11 is powered by a constant voltage, at this time, the current flowing through the temperature compensation resistor Rs and the Wheatstone bridge 11 becomes smaller, and the temperature compensation resistor Rs and the Wheatstone bridge 11 are in a series relationship, so the voltage of the temperature compensation resistor Rs decreases. Correspondingly, the voltage of the Wheatstone bridge 11 increases, the voltage input to the amplifier element increases, and correspondingly, the voltage output by the amplifier element also increases, thereby playing a role in temperature compensation. Moreover, this temperature compensation is dynamic and changes with the temperature change of the Wheatstone bridge 11, so that the slope (sensitivity) of the output voltage-measured pressure line graph of the pressure sensor at different temperatures tends to be consistent (the slope of the output voltage-measured pressure line graph under constant temperature conditions tends to be consistent with the standard temperature). In addition, the supply current of the Wheatstone bridge 11 is sampled through the sampling resistor R8 and then converted into a sampling voltage. The sampling voltage is directly proportional to the zero voltage source V adjThe voltage difference is amplified by the operational amplifier U4, and the sampling voltage changes with the temperature change of the Wheatstone bridge 11. Therefore, the voltage output by the operational amplifier U4 to the zero adjustment terminal of the instrumentation amplifier U1 also changes dynamically, thereby realizing dynamic zero adjustment.

[0032] The principle of the present invention is as follows: under constant temperature conditions of standard temperature (preferably, +25°C), first, a constant voltage power supply mode is adopted, and the current of the Wheatstone bridge 11 is used as a feedback signal to adjust the output offset of the instrument amplifier U1, thereby correcting the output temperature drift of the pressure sensor caused by temperature changes; second, a fixed resistor (temperature compensation resistor Rs) is connected in series between the power supply end of the Wheatstone bridge 11 and the constant voltage power supply to adjust the sensitivity of the sensor; third, the output voltage of the instrument amplifier U1 is returned to zero when the measured pressure is zero through the zero adjustment unit; finally, the gain resistor R G , so that the output voltage value of the instrumentation amplifier U1 (in mV) is consistent with the measured pressure value of the sensor (in kPa).

[0033] With the above solution, the output voltage of the Wheatstone bridge 11 is amplified only by the instrumentation amplifier U1. By using an instrumentation amplifier U1 with a large bandwidth, it is possible to ensure that the pressure sensor has a large bandwidth. Preferably, in this embodiment, the bandwidth of the instrumentation amplifier U1 is required to be no less than 0.1 MHz, and preferably, the bandwidth of the instrumentation amplifier U1 is 1 MHz.

[0034] A MEMS pressure sensor equipped with a compensation module 30 was tested under different ambient temperatures, with a full-scale forward and reverse pressure range of 500 kPa. The pressure applied to the pressure sensor was the nitrogen pressure (in kPa) supplied by a pressure controller. Table 1 shows the test results for the pressure sensor equipped with the compensation circuit of the present invention, under a full-scale forward and reverse pressure range of 500 kPa at temperatures of 25°C, 70°C, 150°C, 180°C, and 220°C. As shown in Table 1, the DC voltage output of the pressure sensor (in mV) can be used as the measured pressure value (in kPa), with a reading accuracy of ±1%. This direct reading eliminates the need for conventional linear analog calculations, greatly facilitating practical applications. If the direct reading accuracy is allowed to be within ±3%, the compensation temperature range can be extended to 350°C. The compensation module 30 of the present invention ensures high frequency response for leadless packaged pressure sensors.

[0035] Table 1

[0036]

[0037] The above is only a preferred specific implementation method of the present invention, but the protection scope of the present invention is not limited to this. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A temperature compensation circuit for a piezoresistive pressure sensor, characterized in that: The piezoresistive pressure sensor comprises a temperature compensation resistor Rs, an amplifying element, and a zero adjustment unit. The input end of the Wheatstone bridge of the piezoresistive pressure sensor is connected to a constant voltage power supply via the temperature compensation resistor Rs, and the output end of the Wheatstone bridge of the piezoresistive pressure sensor is connected to the input end of the amplifying element. The zero adjustment unit samples the power supply current of the Wheatstone bridge and converts it into a voltage, which is then output to the zero adjustment end of the amplifying unit. The temperature compensation resistor Rs is a fixed-value resistor.

2. The temperature compensation circuit of the piezoresistive pressure sensor according to claim 1, wherein: The amplifying element is an instrumentation amplifier U1.

3. The temperature compensation circuit of the piezoresistive pressure sensor according to claim 1 or 2, characterized in that: The zero adjustment unit includes a sampling resistor R8, an operational amplifier U4 and a zero adjustment voltage source V adj The sampling resistor R8 is connected in series to the front end of the constant voltage power supply, the non-inverting input end of the operational amplifier U4 is connected to the connection between the sampling resistor R8 and the constant voltage power supply, and the zero voltage source V adj The inverting input terminal of the operational amplifier U4 is connected, and the output terminal of the operational amplifier U4 is connected to the zero adjustment terminal of the amplifying element; the zero adjustment voltage source V adj Output constant voltage.

4. The temperature compensation circuit of the piezoresistive pressure sensor according to claim 3, wherein: It also includes a voltage stabilizing chip U3, the output end of the voltage stabilizing chip U3 is the constant voltage power supply, and the sampling resistor R8 is connected in series with the input end of the voltage stabilizing chip U3.

5. The temperature compensation circuit of the piezoresistive pressure sensor according to claim 3, wherein: Also includes the gain resistor R G , the gain resistor R G is a fixed value resistor, the gain resistor R G Connect one end of the instrumentation amplifier U1 to R G - pin, the gain resistor R G The other end of the instrumentation amplifier U1 is connected to the R G + feet.

6. The temperature compensation circuit of the piezoresistive pressure sensor according to claim 2, wherein: The bandwidth of the instrumentation amplifier U1 is not less than 0.1 MHz.

7. A piezoresistive pressure sensor using the temperature compensation circuit according to any one of claims 1 to 6.

8. The piezoresistive pressure sensor according to claim 7, wherein: It includes a sensor body, a connecting cable and a compensation module. The sensor body is provided with a Wheatstone bridge. The temperature compensation resistor Rs, the amplifying element and the zero adjustment unit are arranged on the compensation module. The constant voltage power supply, the temperature compensation resistor Rs and the amplifying element are connected to the Wheatstone bridge via the connecting cable.

9. The piezoresistive pressure sensor according to claim 8, wherein: The connecting cable is a high temperature resistant cable.

10. The piezoresistive pressure sensor according to claim 8, wherein: The length of the connecting cable is not less than 0.5m.

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