CN217738500U - Conditioning circuit of piezoresistive pressure sensor - Google Patents
Conditioning circuit of piezoresistive pressure sensor Download PDFInfo
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- CN217738500U CN217738500U CN202222052278.6U CN202222052278U CN217738500U CN 217738500 U CN217738500 U CN 217738500U CN 202222052278 U CN202222052278 U CN 202222052278U CN 217738500 U CN217738500 U CN 217738500U
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Abstract
The utility model discloses a piezoresistive pressure sensor's conditioning circuit belongs to sensor technical field. The design comprises an amplifying circuit design for outputting signals to a pressure sensor, wherein the amplifying circuit design adopts three operational amplifiers OP77 to form an instrument amplifier module, a front-stage two operational amplifier circuit mainly carries out interference removal and preliminary amplification on the signals, a rear-stage operational amplifier carries out high-gain amplification on the signals, one pin of two input ends of the instrument amplifier is connected with the output signals of a sensor chip, the other end of the two input ends of the instrument amplifier is connected with a voltage regulating circuit, a sliding rheostat is used for carrying out voltage division on the voltages, and then proper voltage is taken out and input to the input end of the amplifying circuit to serve as a clamping voltage for fixing the output voltage range of the module. Compared with the prior art, this application still designs the power supply and the circuit temperature drift suppression of circuit to pressure sensor temperature characteristic, and the measuring error that effectual suppression temperature arouses in the circuit compares in software compensation, and hardware circuit temperature compensation is more convenient and real-time compensation.
Description
Technical Field
The utility model relates to a sensor technical field, concretely relates to piezoresistive pressure sensor's conditioning circuit.
Background
The sensor plays an important role in the fields of automatic detection, automatic control systems and the like, and has the function of sensing and collecting signals. For example, in a relay valve braking system test bed, the most important thing is to realize the conversion of electric signals, the pressure sensor module is used as one of the important rings, and the accuracy and the stability of the signals are all important. The original output signal of the piezoresistive pressure sensor belongs to a weak signal, is easily interfered by a noise signal, and is not beneficial to subsequent acquisition and utilization. Meanwhile, the device is easily influenced by temperature in the test process. Therefore, proper conditioning methods are needed to solve these characteristics. At present, aiming at the design of a conditioning circuit of a pressure sensor, the stability of the conditioning circuit is emphasized, most of common circuits are temperature compensation or gain compensation on a software algorithm, most of the circuits are complex, and the compensation precision is limited.
The amplification gain of the output signal of the sensor is also important, and the radio frequency interference existing between the sensor and the multistage amplification circuit and the offset voltage of the input end of the amplifier are also considered when the signal is sampled and output.
SUMMERY OF THE UTILITY MODEL
To the not enough of prior art, the utility model provides a piezoresistive pressure sensor's conditioning circuit. Temperature compensation is carried out on a hardware circuit, the influence of temperature on the input signal of the sensor is eliminated by selecting a proper power supply circuit, so that the stability of signal acquisition is ensured, an amplification gain module of a system is further improved, an instrumentation amplifier circuit consisting of three operational amplifiers is used for enhancing the acquired signal, and radio frequency interference between the sensor and the instrumentation amplifier is effectively filtered through a filter circuit; and an ADC analog-to-digital conversion circuit is selected, so that signals amplified by the sensor are collected and provided to the single chip microcomputer for processing and displaying.
The purpose of the utility model can be realized by the following technical scheme: the device comprises an instrument amplifier module, a power supply circuit and an ADC signal acquisition circuit;
the instrument amplifier module adopts a three-operational amplifier circuit design, a front-stage operational amplifier circuit is used for carrying out interference removal and preliminary amplification on signals, and a rear-stage operational amplifier circuit is used for carrying out high-gain amplification on the signals;
the instrument amplifier module includes voltage regulating circuit, instrument amplifier, slide rheostat, low pass filter circuit, switch diode, an input end foot of two operational amplifier circuit in instrument amplifier's preceding stage connects sensor chip's output signal, a voltage regulating circuit is connected to another input of two operational amplifier circuit in instrument amplifier's preceding stage, two operational amplifier circuit's in instrument amplifier's preceding stage output and two input connections of instrument amplifier's back level operational amplifier circuit, instrument amplifier is differential input, two input low pass filter circuit of two operational amplifier circuit in instrument amplifier's preceding stage, a switch diode is connected at the output to instrument amplifier's back level operational amplifier circuit.
Furthermore, the power supply circuit is a power supply input circuit of the instrumentation amplifier module, and the input power supply signal is subjected to anti-interference processing to generate various power supply signals required by the instrumentation amplifier module;
the power supply circuit comprises a power supply conversion module, a 12V power supply is input into the power supply conversion module, the voltage signal input is converted through a fixed voltage three-terminal integrated voltage stabilizer, 5V voltage is output, the output end of the power supply conversion module is connected with a constant current source circuit, a peripheral circuit of the constant current source circuit is connected with two resistors and a diode to form a temperature compensation circuit, and one resistor and one diode are connected with the other resistor in parallel.
Further, the ADC signal acquisition circuit is used for acquiring and converting the output signal of the pressure sensor module; the ADC signal acquisition circuit is connected with the output end of the instrumentation amplifier module, and an analog-to-digital conversion chip adopted by the ADC signal acquisition circuit supports the acquisition of 8 paths of signals and converts the output voltage of the instrumentation amplifier.
Furthermore, the voltage regulating circuit utilizes the slide rheostat to divide voltage, and then takes out proper voltage to be input to the input end of the instrument amplifier module to serve as clamping voltage for fixing the output voltage range of the module.
Furthermore, the instrumentation amplifier module adopts a symmetrical design to suppress interference of common mode signals and suppress voltage offset.
Furthermore, the switching diode protects the output signal, a range is regulated for the output voltage, the damage of a preceding stage circuit is prevented, and therefore the output voltage is too large and a lower stage circuit is damaged.
Furthermore, the instrumentation amplifier needs positive and negative power supplies, a chip for inverting the voltage is adopted in the instrumentation amplifier module to provide negative voltage, a 5V voltage signal output by the integrated voltage stabilizer with three fixed voltage ends is connected to the input end of a chip circuit for inverting the voltage, and the voltage is subjected to polarity conversion by the chip for inverting the voltage so that the output voltage of the instrumentation amplifier module is equal to the voltage of the input end of the chip for inverting the voltage.
Further, before the constant current source is connected, the circuit provides 5V power supply voltage through a linear stabilized voltage power supply 78L05 chip circuit, the chip adopted by the constant current source circuit is LM134, and the current generated by the chip is related to the temperature according to a chip characteristic manual, so that when the current source is designed, a peripheral circuit is required to be designed to eliminate the influence of the temperature, the current source is realized by adopting a mode of adding a resistor and a diode, and the temperature drift of the diode 1N457 and the LM134 can be mutually offset according to the temperature coefficient calculation of the diode. In addition, the pressure sensor MPX5999D selected by the design has a temperature compensation function within the range of 0-85 ℃. Thus, both together eliminate the effect of temperature on the pressure signal.
Furthermore, a split-board design is adopted between the instrument amplifier module and the ADC signal acquisition circuit, and certain interference signals can be formed on the design of the integrated circuit and the external environment; the instrument amplifier module is connected with a low-pass filter circuit at the signal input part, the low-pass filter circuit adopts a second-order RC low-pass filter circuit, and the second-order RC low-pass filter circuit attenuates the input high-frequency signal, so that the low-frequency signal can stably pass through the low-pass filter circuit.
The utility model has the advantages that:
(1) The power supply and the circuit temperature drift suppression of the circuit are designed aiming at the temperature characteristic of the pressure sensor, the measurement error caused by temperature can be effectively suppressed in the circuit, and compared with software compensation, the hardware circuit temperature compensation is more convenient and can be compensated in real time.
(2) Aiming at better guaranteeing the effectiveness of the signals of the pressure sensor, an instrument amplifier consisting of three operational amplifiers is designed to amplify the signals, namely a differential amplifying circuit, the differential amplifying circuit has extremely high common mode rejection ratio, the secondary amplifying circuit part is subjected to rejection design aiming at radio frequency interference signals which are possibly generated, and a variable resistor is added at an input end, so that the control of the multiple of the amplifying circuit can be completed, the problems of low output precision, easy external interference and small conversion gain of a common conditioning amplifying circuit are effectively solved, and a protection measure is added at an output end to prevent the use of a lower circuit from being influenced by abnormal output.
(3) In order to ensure that the single chip microcomputer can acquire accurate pressure signals, a 12-bit high-precision AD7606 sampling chip is adopted, the energy consumption is low, error correction can be completed, and external adjustment is not needed. The design adopts the internal reference voltage without adding a reference voltage circuit, thereby ensuring the integration and miniaturization of the circuit board. And the external interference and aliasing phenomena are considered, and a second-order RC circuit is adopted to carry out high-frequency filtering on the signal, so that the module cost is effectively controlled while the working precision requirement is ensured.
Drawings
The present invention will be further described with reference to the accompanying drawings.
FIG. 1 is a block flow diagram of the overall conditioning circuit design of the present application;
FIG. 2 is a schematic diagram of the circuit design of the power supply portion of the present application;
FIG. 3 is a schematic diagram of a voltage inverting circuit within the circuit of the present application;
FIG. 4 is a schematic diagram of the circuit design of an instrumentation amplifier module comprising three operational amplifiers according to the present application;
FIG. 5 is a circuit diagram of the A/D analog-to-digital conversion circuit of the present application;
FIG. 6 is a diagram of an 8-way second order RC filter circuit of the present application;
fig. 7 is a schematic diagram of the conditioning circuit of the present application as a soldered PCB board.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.
In a specific embodiment, when designing a piezoresistive pressure sensor signal acquisition module, firstly, the type of chips such as a sensor used by the module is selected, and after the type selection of the sensor chip is finished, a driving circuit and a signal conversion circuit of the piezoresistive pressure sensor signal acquisition module need to be designed, as shown in fig. 1, the main design part is the design of supplying power by a constant current source and effectively amplifying a sensor signal by an instrumentation amplifier.
The power supply circuit is a power supply input circuit of the module, input power supply signals generate various power supply signals required by the circuit module after being subjected to anti-interference processing, the processed power supply signals and voltage signals converted by the sensor are further processed by the instrumentation amplifier to obtain voltage signals, the voltage signals are transmitted to the single chip microcomputer through the AD analog-to-digital conversion module to be processed, and finally a real-time pressure curve is displayed on an upper computer, and the working mode of the module is described in detail below.
Under the condition of ensuring that a main power supply is normal, a 12V power supply is input into a power supply conversion module, an input voltage signal is converted through a 78L05, a 5V voltage is output, compared with the direct power supply of a common constant voltage source, the temperature influence of a circuit is difficult to eliminate, therefore, the design connects the output end of the 78L05 with a constant current source circuit, the output end of the 78L05 is processed through an LM134 chip, a temperature compensation circuit design is formed by adding a diode to two resistors of a peripheral circuit of the LM134, and the temperature drift of the LM134 and the peripheral circuit of the LM134 is balanced and eliminated through calculation and analysis of a temperature coefficient (-2.5 mV/. Degree.C.) of the carried-in diode when the circuit meets the following formula, referring to the attached figure 2, the circuit of figure 2 consists of two parts, namely a main 5V power supply output circuit and a sensor current source power supply circuit.
In which I 1 To flow through R 11 Is approximately expressed as the current flowing through the diode, I 2 Represents a flow through R 12 When the following formula is satisfied, the selected sensor chip can carry out temperature compensation within a certain range, and the current and the sensor chip jointly eliminate the influence of temperature on the pressure signal.
In addition, since the operational amplifier needs a negative power supply, the 5V voltage signal output by 78L05 needs to be connected to the input terminal of the ic 7660 circuit of the chip, and the polarity of the voltage can be converted by the ic 7660 circuit to make VOUT = -VIN, as shown in the attached drawing3, wherein the electrolytic capacitor E is arranged at the periphery 1 、E 2 Is an external energy storage capacitor of the chip, C 9 、C 10 Is a filter capacitor.
The constant current signal is output to the sensor through the LM314 for power supply, furthermore, the sensor transmits a signal generated by measuring air pressure to an instrument amplifier circuit module, the instrument amplifier is IN differential input, one negative input port (IN 1) is connected with a slide rheostat and then connected with a 5v power supply, so that an adjustable clamping voltage is input to a port, the output range of the whole module is controlled, the other end (IN 2) of the amplifier is connected with signal input of the sensor, a low-pass filter circuit design is firstly connected to two ports, radio frequency interference signals are filtered, the whole amplifying circuit is IN a symmetrical design, namely, an internal resistor R is arranged 3 ＝R 7 、R 4 ＝R 6 、R 2 ＝R 8 ，R 9 ＝R 10 ，C 1 ＝C 3 ，R 0 For adjusting the amplification, C, of instrumentation amplifiers 2 Has the function of reducing the matching requirement of two low-pass filter cut-off frequencies, and the value of the low-pass filter cut-off frequency is about C 1 The output voltage calculation and the difference bandwidth and common mode bandwidth calculation are as follows, the operational amplifiers of the two input ends of the module perform basic amplification firstly, and the input impedance of the whole instrument amplification circuit tends to infinity, so compared with a common operational amplifier circuit, the instrument amplification circuit adopted by the design has the excellent characteristics of high input impedance, high common mode rejection ratio and the like, radio frequency interference suppression is performed on the circuit, the accuracy and stability of an output signal are improved, the two primary operational amplifiers are amplified and then input into a high-gain amplifier at the rear end for accurate amplification, the output is connected into the MMBD7000 finally, the MMBD7000 consists of two diodes at the upper part and the lower part, and when the output voltage is overlarge, the diodes can be conducted to prevent the output voltage from being overlarge and damaging a lower circuit. Vout in the following formula 1 ，Vout 2 ，Vin 1 ，Vin 2 Vout is respectively represented as U shown in FIG. 1 1 ，U 2 Output voltage, input voltage and output voltage of the entire instrumentation amplifier, D 1 Representing differential bandwidth, D 2 Representing common mode bandwidthReference is made to fig. 2.
Further, after the amplifier is output, the signal is connected to a second-order filter circuit, and due to the design of the integrated circuit and the fact that a certain interference signal is formed in the external environment, the output information of the integrated circuit is also easily affected by noise, the second-order RC low-pass filter design is carried out on the signal input part of the integrated circuit, and therefore the low-frequency signal can stably pass through the integrated circuit, as shown in the attached drawing 4, the integrated circuit is symmetrically designed, namely the capacitance and resistance values of the upper part and the lower part are the same. For 8 input and output paths relative to ADC sampling, as shown in fig. 6, eight input ports corresponding to the analog-to-digital conversion circuit respectively perform a high-frequency filtering process, and then lead to the ADC module.
And in the next step, the filtered signals are input into an ADC7606 module for analog-to-digital conversion, and finally are calculated and output to a single chip microcomputer for further processing and display. As shown in FIG. 5, after the sensor signal is amplified, the output port of the meter sensor is connected to AD7606 fine analog-to-digital conversion, and the input conversion of 8 sensor signals can be simultaneously supported. The input-output calculation is as follows.
Wherein Vout in the formula represents the voltage signal, U, output by the instrumentation amplifier ADC Representing reference voltage of ADC, number of bits is N, and measuring range is D 1 。
As shown in FIG. 7, the circuit board punching schematic diagram is a front and back surface component, which is convenient for packaging for integration miniaturization, and the utility model discloses independently punch the circuit board, the external processing of analog-to-digital conversion circuit board part.
In the description of the present invention, it is to be understood that the terms "open hole", "upper", "lower", "thickness", "top", "middle", "length", "inner", "around", etc. indicate an orientation or positional relationship only for the convenience of description of the present invention and to simplify the description, and do not indicate or imply that the component or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present invention.
In the description herein, references to the description of "one embodiment," "an example," "a specific example," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the above embodiments, and that the foregoing embodiments and descriptions are provided only to illustrate the principles of the present invention without departing from the spirit and scope of the present invention.
Claims (9)
1. A conditioning circuit of a piezoresistive pressure sensor is characterized by comprising an instrument amplifier module, a power supply circuit and an ADC signal acquisition circuit;
the instrument amplifier module adopts a three-operational-amplifier design, the two operational amplifier circuits at the front stage are used for carrying out interference removal and primary amplification on signals, and the operational amplifier circuits at the rear stage are used for carrying out high-gain amplification on the signals;
the instrument amplifier module includes voltage regulating circuit, instrument amplifier, slide rheostat, low pass filter circuit and switch diode, an input pin of two operational amplifier circuit in instrument amplifier's preceding stage meets sensor chip's output signal, a voltage regulating circuit is connected to another input of two operational amplifier circuit in instrument amplifier's preceding stage, two operational amplifier circuit's in instrument amplifier's preceding stage output and two input of instrument amplifier's back level operational amplifier circuit are connected, instrument amplifier is differential input, two input low pass filter circuit of two operational amplifier circuit in instrument amplifier's preceding stage, a switch diode is connected at the output to instrument amplifier's back level operational amplifier circuit.
2. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the power supply circuit is a power supply input circuit of the instrumentation amplifier module, and the input power supply signal is subjected to anti-interference processing to generate various power supply signals required by the instrumentation amplifier module;
the power supply circuit comprises a power supply conversion module, a 12V power supply is input into the power supply conversion module, the voltage signal input is converted through a fixed voltage three-terminal integrated voltage stabilizer, 5V voltage is output, the output end of the power supply conversion module is connected with a constant current source circuit, a peripheral circuit of the constant current source circuit is connected with two resistors and a diode to form a temperature compensation circuit, and one resistor and one diode are connected with the other resistor in parallel.
3. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the ADC signal acquisition circuit is used for acquiring and converting the output signal of the pressure sensor module; the ADC signal acquisition circuit is connected with the output end of the instrumentation amplifier module, and an analog-to-digital conversion chip adopted by the ADC signal acquisition circuit supports the acquisition of 8 paths of signals and converts the output voltage of the instrumentation amplifier.
4. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the voltage regulating circuit divides the voltage by using a slide rheostat, and then takes out a proper voltage to input to the input end of the instrumentation amplifier module as a clamping voltage for fixing the output voltage range of the module.
5. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the instrumentation amplifier module is designed symmetrically to suppress common mode signal interference and suppress voltage offset.
6. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the switching diode protects the output signal to define a range for the output voltage.
7. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein the instrumentation amplifier requires positive and negative power supplies, a voltage-inverting chip is used inside the instrumentation amplifier module to provide negative voltage, a 5V voltage signal output by the three-terminal integrated voltage regulator is connected to the input end of the voltage-inverting chip circuit, and VOUT = -VIN is obtained by inverting the polarity of the voltage by the voltage-inverting chip.
8. The conditioning circuit of a piezoresistive pressure sensor according to claim 1, wherein said piezoresistive pressure sensor comprises a wheatstone bridge inside, and when the sensor uses a constant current source to supply power to the sensor.
9. The conditioning circuit of the piezoresistive pressure sensor according to claim 1, wherein a splitter is arranged between the instrumentation amplifier module and the ADC signal acquisition circuit, the low-pass filter circuit is a second-order RC low-pass filter circuit, and the second-order RC low-pass filter circuit attenuates the input high-frequency signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202222052278.6U CN217738500U (en) | 2022-08-05 | 2022-08-05 | Conditioning circuit of piezoresistive pressure sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202222052278.6U CN217738500U (en) | 2022-08-05 | 2022-08-05 | Conditioning circuit of piezoresistive pressure sensor |
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| Publication Number | Publication Date |
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| CN217738500U true CN217738500U (en) | 2022-11-04 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202222052278.6U Active CN217738500U (en) | 2022-08-05 | 2022-08-05 | Conditioning circuit of piezoresistive pressure sensor |
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- 2022-08-05 CN CN202222052278.6U patent/CN217738500U/en active Active
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