Constant current source for supplying power to piezoresistive pressure sensor

Abstract

The invention belongs to the technical field of constant current source power supply. The constant current source comprises an operational amplifier, a P-MOS (P-Metal Oxide Semiconductor) tube, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor and an ADC (Analog to Digital Converter) module for acquiring output voltage of the sensor, the reference voltage of the constant current source circuit is simultaneously used as the reference voltage input of an analog-to-digital converter (ADC) module of the sensor output voltage acquisition circuit, so that the influence of constant source reference voltage fluctuation on the measured value of the output voltage of the pressure sensor is eliminated, and the pressure measurement precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of constant current source power supply, and in particular to a constant current source for powering a piezoresistive pressure sensor. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Piezoresistive pressure sensor is one of the most commonly used pressure sensors, with the advantages of high sensitivity, high linearity, small size, high reliability, and suitability for dynamic measurement. It is widely used in aircraft aerodynamic environment measurement, engine performance testing, shock wave measurement, oil well pressure measurement, etc. With the continuous improvement of sensor accuracy requirements in aircraft aerodynamic pressure measurement and other applications, the stability of the power supply has become one of the important factors limiting the accuracy of piezoresistive pressure sensors.

[0004] Constant current source power supply is a commonly used power supply method for piezoresistive pressure sensors. However, traditional constant current source power supply easily causes the sensor output voltage measurement value to be affected by changes in the reference voltage of the constant current source circuit, limiting the improvement of sensor accuracy and stability. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a constant current source for powering a piezoresistive pressure sensor. By using the reference voltage of the constant current source circuit as the reference voltage input of the analog-to-digital converter (ADC module) of the sensor output voltage acquisition circuit, the influence of the constant current source reference voltage fluctuation on the output voltage measurement value of the pressure sensor is eliminated, thereby improving the pressure measurement accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a constant current source for powering a piezoresistive pressure sensor.

[0008] A constant current source for powering a piezoresistive pressure sensor, comprising: an operational amplifier, a P-MOS tube, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and an ADC module for collecting the output voltage of the sensor;

[0009] The supply voltage is connected to the second resistor and the fifth resistor respectively, the second resistor is connected to the positive input terminal of the operational amplifier and the third resistor respectively, and the third resistor is grounded;

[0010] The fifth resistor is connected to the fourth resistor and the source of the P-MOS tube respectively, the fourth resistor is connected to the negative input terminal of the operational amplifier, the gate of the P-MOS tube is connected to the output terminal of the operational amplifier, and the drain of the P-MOS tube is used to be connected to the input terminal of the piezoresistive pressure sensor;

[0011] The reference voltage is connected to the first resistor and the ADC module respectively. The first resistor is connected to the negative input terminal of the operational amplifier. The input terminal of the ADC module is used to be connected to the output terminal of the piezoresistive pressure sensor.

[0012] As a further limitation of the present invention, the reference voltage is used as a reference voltage of the operational amplifier and also as a reference voltage of the ADC module.

[0013] As a further limitation of the present invention, it is assumed that the source position of the P-MOS tube is point b, the gate position of the P-MOS tube is point c, and the negative input terminal position of the operational amplifier is point a;

[0014] When the output current becomes smaller, the source current of the P-MOS tube decreases, the potential at point b rises, and is fed back to the negative input terminal of the operational amplifier through the fourth resistor. The potential at point a rises, the difference between the two input terminals of the operational amplifier decreases, the output voltage of the operational amplifier decreases, the gate potential at point c decreases, and the P-MOS tube adjusts the on-resistance to increase the output current, thereby achieving constant load current.

[0015] As a further limitation of the present invention, the piezoresistive pressure sensor adopts a Wheatstone bridge, comprising R b1 , R b2 , R b3 and R b4 , R b2 and R b3 The connection position is grounded, R b1 With R b4 The connection position is connected to the drain of the P-MOS tube, R b3 and R b4 The connection position is connected to the positive input terminal of the ADC module, R b1 and R b2 The connection position is connected to the negative input terminal of the ADC module.

[0016] As a further limitation of the present invention, the resistance change D of the piezoresistive pressure sensor is:

[0017]

[0018] Where ΔR is R b1 , R b2 , R b3 and R b4 The change in resistance value, R 5 is the fifth resistor, and n is the number of bits of ADC.

[0019] As a further limitation of the present invention, R b1 , R b2 , Rb3 and R b4 The resistance value is the same.

[0020] As a further limitation of the present invention, the output voltage formula of the piezoresistive pressure sensor is:

[0021]

[0022] Among them, V ref is the reference voltage.

[0023] As a further limitation of the present invention, the second resistor is equal to the third resistor, and the first resistor is equal to the fourth resistor.

[0024] In a second aspect, the present invention provides a piezoresistive pressure sensor, which is powered by the constant current source for powering the piezoresistive pressure sensor described in the first aspect of the present invention.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention innovatively uses the constant current source circuit reference voltage as the reference voltage input of the analog-to-digital converter (ADC) of the sensor output voltage acquisition circuit, thereby eliminating the influence of the constant current source reference voltage fluctuation on the output voltage measurement value of the pressure sensor and improving the pressure measurement accuracy.

[0027] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 A schematic diagram of the principle of a constant current source for powering a piezoresistive pressure sensor provided in Example 1 of the present invention;

[0030] Figure 2 This is a wiring diagram of a constant current source for powering the piezoresistive pressure sensor provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0033] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0034] Embodiment 1:

[0035] The stability of the constant current source directly affects the output accuracy of the piezoresistive pressure sensor. In this implementation, a constant current source for powering the piezoresistive pressure sensor is proposed, including an operational amplifier, a high-precision voltage regulator VCC, precision resistors R1 (i.e., the first resistor), R2 (i.e., the second resistor), R3 (i.e., the first resistor), R4 (i.e., the fourth resistor), R5 (i.e., the fifth resistor) and a P-MOS tube to achieve conversion from constant voltage to constant current.

[0036] The supply voltage VCC is connected to the second resistor R2 and the fifth resistor R5 respectively, the second resistor R2 is connected to the positive input terminal of the operational amplifier and the third resistor R3 respectively, and the third resistor R3 is grounded;

[0037] The fifth resistor R5 is connected to the fourth resistor R4 and the source of the P-MOS tube respectively, the fourth resistor R4 is connected to the negative input terminal of the operational amplifier, the gate of the P-MOS tube is connected to the output terminal of the operational amplifier, and the drain of the P-MOS tube is used to be connected to the input terminal of the piezoresistive pressure sensor;

[0038] The reference voltage is connected to the first resistor R1 and the ADC module respectively. The first resistor R1 is connected to the negative input terminal of the operational amplifier. The input terminal of the ADC module is used to be connected to the output terminal of the piezoresistive pressure sensor.

[0039] Figure 1 In, V ref is the high-precision reference voltage of the constant current source, Iout is the output current of the constant current source, and VCC is the supply voltage. In order to achieve the purpose of constant current, the circuit needs to be regulated by negative feedback. The regulation process is that when the output current Iout becomes smaller, in an ideal case, the drain current of the P-MOS tube is equal to the source current. At this time, the source current of the P-MOS tube decreases, then Figure 1 The potential at point b rises, and the feedback resistor R 4 Feedback to the negative input of the operational amplifier, that is Figure 1 The potential at point a rises, and the difference between the two input terminals of the operational amplifier decreases, so the output voltage of the operational amplifier will decrease, that is, Figure 1 When the gate potential at point c in the circuit decreases, the P-MOS tube will adjust its on-resistance to increase the output current Iout, thereby achieving the purpose of constant load current.

[0040] Under ideal conditions, according to the "virtual short" and "virtual open" principles of the operational amplifier, that is, the voltages at the two input terminals of the operational amplifier are equal and the input current is zero, the following formula can be obtained:

[0041]

[0042] Where V b is the voltage at the point in the diagram.

[0043] Simplifying the above formula, we can get:

[0044] V ref =VCC-V b (2)

[0045] So the output current is:

[0046]

[0047] For the sensor, according to the principle of piezoresistive pressure sensor, when powered by a constant current source, the output voltage of the Wheatstone bridge is:

[0048]

[0049] Assume that when R b1 =R b2 =R b3 =R b4 =R, when the change in resistance of each resistor is ΔR, we can get:

[0050] ΔV=I out *ΔR(5);

[0051] It can be seen from equation (5) that, ideally, the output voltage ΔV of the Wheatstone bridge is proportional to the change ΔR of the resistance under stress, and the stability of the constant current source will directly affect the output accuracy of the bridge.

[0052] Substituting equation (3) into equation (5), we can get the output voltage of the pressure sensor as:

[0053]

[0054] It can be seen from equation (6) that the accuracy of the pressure sensor will be different from the reference voltage V ref and resistor R 5 In order to eliminate the reference voltage V ref The influence of the pressure sensor output accuracy is to adjust the reference voltage V ref At the same time, it is used as the reference voltage input of ADC, so that ADC uses the reference voltage V ref Quantize the analog signal. After ADC quantization encoding, the output voltage formula of the measured pressure sensor can be obtained as follows:

[0055]

[0056] Where D is the digital value after ADC encoding; n is the number of bits of ADC.

[0057] Combining equation (6) with equation (7), we can get the change in resistance of the pressure sensor as:

[0058]

[0059] From equation (8), we can see that the measured digital value of the pressure sensor is only related to the resistance R 5 It is related to the number of ADC bits. Here, the reference voltage V ref At the same time, as a method of reference voltage input for ADC, the error caused by the reference voltage fluctuation of the constant current source circuit to the sensor output signal measurement is eliminated.

[0060] Therefore, the accuracy of measuring resistance change is related to the resistance R 5 When designing the constant current source module, the invention calculates the resistance R according to the parameters of the sensor. 5 Use low temperature drift and high precision resistors. In order to meet the resistor R 5 The voltage difference between the two ends is the reference voltage V ref , the resistor R 2 and R 3 Equal, resistance R 1 and R 4 Therefore, a low temperature drift and high precision resistor matching network is used in the design. In addition, for the selection of operational amplifiers, it is best to use one with excellent DC performance. The above measures comprehensively guarantee the superior performance of the constant current source and improve the measurement accuracy and stability of the piezoresistive pressure sensor.

[0061] According to the above requirements, this implementation method designs a specific constant current source circuit diagram, such as Figure 2 As shown. The ADC uses TI's eight-channel synchronous sampling ADS1278, which has a 24-bit resolution and a sampling rate of up to 144kSPS. This type of ADC uses incremental encoding for quantization encoding, with high resolution and high conversion rate. The resistor matching network in the constant current source module is implemented using the low-temperature drift, high-precision LT5400ACMS8E-3#PBF. The resistor R 5 It is realized by using low temperature drift and high precision resistor Y16291K00000B9R, with deviation ±0.1% and temperature coefficient ±0.2ppm / ℃. The reference voltage VREFP of ADC device ADS1278 is also used as the reference voltage of constant current source module, eliminating the influence of constant current source error on the output voltage measurement value of piezoresistive pressure sensor.

[0062] Embodiment 2:

[0063] This implementation provides a piezoresistive pressure sensor, which is powered by the constant current source for powering the piezoresistive pressure sensor described in Example 1 of the present invention.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A constant current source for powering a piezoresistive pressure sensor, characterized in that: It includes: an operational amplifier, a P-MOS tube, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and an ADC module for collecting the output voltage of the sensor; The supply voltage is connected to the second resistor and the fifth resistor respectively, the second resistor is connected to the positive input terminal of the operational amplifier and the third resistor respectively, and the third resistor is grounded; The fifth resistor is connected to the fourth resistor and the source of the P-MOS tube respectively, the fourth resistor is connected to the negative input terminal of the operational amplifier, the gate of the P-MOS tube is connected to the output terminal of the operational amplifier, and the drain of the P-MOS tube is used to be connected to the input terminal of the piezoresistive pressure sensor; The reference voltage is connected to the first resistor and the ADC module respectively. The first resistor is connected to the negative input terminal of the operational amplifier. The input terminal of the ADC module is used to be connected to the output terminal of the piezoresistive pressure sensor.

2. The constant current source for powering a piezoresistive pressure sensor according to claim 1, characterized in that: The reference voltage is used as the reference voltage of the operational amplifier and also as the reference voltage of the ADC module.

3. The constant current source for powering a piezoresistive pressure sensor according to claim 1, characterized in that: Assume that the source position of the P-MOS tube is point b, the gate position of the P-MOS tube is point c, and the negative input terminal position of the operational amplifier is point a; When the output current becomes smaller, the source current of the P-MOS tube decreases, the potential at point b rises, and is fed back to the negative input terminal of the operational amplifier through the fourth resistor. The potential at point a rises, the difference between the two input terminals of the operational amplifier decreases, the output voltage of the operational amplifier decreases, the gate potential at point c decreases, and the P-MOS tube adjusts the on-resistance to increase the output current, thereby achieving constant load current.

4. The constant current source for powering a piezoresistive pressure sensor according to claim 1, characterized in that: The piezoresistive pressure sensor uses a Wheatstone bridge circuit, which consists of R b1 , R b2 , R b3 and R b4 , R b2 and R b3 The connection position is grounded, R b1 With R b4 The connection position is connected to the drain of the P-MOS tube, R b3 and R b4 The connection position is connected to the positive input terminal of the ADC module, R b1 and R b2 The connection position is connected to the negative input terminal of the ADC module.

5. The constant current source for powering a piezoresistive pressure sensor according to claim 4, characterized in that: The resistance change D of the piezoresistive pressure sensor is: Where ΔR is R b1 , R b2 , R b3 and R b4 The change in the resistance value of the resistor, R5 is the fifth resistor, and n is the number of bits of the ADC.

6. The constant current source for powering a piezoresistive pressure sensor according to claim 5, characterized in that: R b1 , R b2 , R b3 and R b4 The resistance value is the same.

7. The constant current source for powering a piezoresistive pressure sensor according to claim 5, characterized in that: The output voltage formula of the piezoresistive pressure sensor is: Among them, V ref is the reference voltage.

8. The constant current source for powering a piezoresistive pressure sensor according to any one of claims 1 to 7, characterized in that: The second resistor is equal to the third resistor, and the first resistor is equal to the fourth resistor.

9. A piezoresistive pressure sensor, characterized in that: The piezoresistive pressure sensor is powered by a constant current source as described in any one of claims 1 to 8.

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