Pulse width modulation silicon resonant pressure sensor closed-loop circuit and debugging method

Abstract

The invention relates to a pulse width modulation silicon resonant pressure sensor closed-loop circuit and a debugging method, the pulse width modulation silicon resonant pressure sensor closed-loop circuit comprises a resonant sensor, a current and voltage conversion circuit, a comparator circuit, an amplitude control circuit and a pulse width modulation generation circuit, and the comparator circuit converts the amplified frequency signal into a square wave signal, generates a pulse signal through the pulse width modulation generation circuit, and is connected to the driving end of the resonator to generate a driving signal to form a closed-loop system. Wherein the amplitude control circuit is used for detecting the signal amplitude of the sensor and generating a control signal to adjust the impedance of the pulse width modulation generation circuit so as to adjust the pulse width of the driving signal and finally realize the stable closed loop of the sensor. According to the method of the closed-loop circuit based on pulse width modulation, the structure of the closed-loop driving circuit is optimized, the number of components is reduced, the pull-in risk is reduced, and the stability of the closed loop is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of resonant MEMS pressure sensors, and in particular relates to a pulse width modulated silicon resonant pressure sensor closed-loop circuit and a debugging method. Background Art

[0002] High-precision resonant pressure sensors are widely used in aerospace, industrial control and other fields. They are composed of a silicon resonant pressure sensitive core and a closed-loop circuit, and usually have requirements such as fast startup, low noise and high reliability. The closed-loop circuit is used to excite the resonator to vibrate and generate an oscillation signal of the resonator's natural frequency, thereby stably outputting a frequency signal related to pressure.

[0003] The resonant closed-loop circuit usually adopts AGC automatic gain control technology, which generally detects the output signal amplitude of the resonator and adjusts the driving voltage of the resonator to stabilize the output amplitude of the sensor. The larger the vibration amplitude of the sensor, the higher its signal-to-noise ratio and the more stable the output signal. However, excessive vibration amplitude can easily cause the vibrating parts of the resonator to approach the driving electrode, thereby causing electrostatic attraction and damage. If the vibration amplitude is too small, the signal-to-noise ratio is poor, and the sensor frequency data fluctuates greatly, which makes it difficult to meet the high reliability requirements of aerospace and other fields.

[0004] Li Haijuan and others from Beijing Aerospace proposed a digital phase-locked solution in the paper "Silicon Resonant Pressure Microsensor Closed-Loop System", which shielded stray capacitance technology by improving the symmetry of the excitation signal and other methods to achieve high-resolution capacitance detection. However, debugging is difficult and costly. "A Silicon Resonant Pressure Sensor Closed-Loop Control Circuit and Debugging Method" (CN104764559A) proposed a digital closed-loop control circuit, in which the introduction of an A / D conversion circuit introduces more op amp device noise than an analog circuit, and the structure is more complex.

[0005] Li Yinan and others from the Institute of Electronics of the Chinese Academy of Sciences proposed a simple closed-loop control circuit in the paper "Research on Key Technologies for Improving the Comprehensive Performance of Resonant MEMS Pressure Sensors". The resonator output signal is converted into a voltage signal through an I / V conversion circuit, and then divided into two paths through a gain adjustment circuit. One path is output through a bandpass filter, and the other path drives the resonator to vibrate continuously through an AGC control circuit. However, this circuit involves I / V conversion, precision half-wave rectification, comparator circuit, AGC automatic gain control and other parts. The structure is relatively complex, the circuit noise introduced is relatively large, and in order to improve reliability, the driving amplitude of the automatic gain control is small, and the system startup time is relatively long, which still needs further optimization. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a pulse width modulated silicon resonant pressure sensor closed-loop circuit and debugging method. The closed-loop circuit uses a pulse signal with a large signal amplitude for excitation, has higher instantaneous energy, can achieve rapid oscillation of the resonator, and reduces the use of circuit elements, reduces the noise introduced by the components, and has a higher system signal-to-noise ratio. At the same time, by setting appropriate parameters, it can ensure that the resonator is in linear operation and improve the reliability of the resonator system.

[0007] As an example to achieve the above purpose, the present invention provides a pulse width modulated silicon resonant pressure sensor closed-loop circuit, including a resonant sensor, a current-voltage conversion circuit, a comparator circuit, an amplitude control circuit and a pulse width modulation generating circuit, the output end of the resonant sensor is connected to the input end of the current-voltage conversion circuit, the output end of the current-voltage conversion circuit is respectively connected to the input end of the comparator circuit and the input end of the amplitude control circuit, the output end of the comparator circuit is connected to the input end of the pulse width modulation generating circuit, and the output end of the pulse width modulation generating circuit is connected to the input end of the resonant sensor. Among them, the pulse width modulation generating circuit includes a first capacitor, a first resistor and a first field effect transistor, the first field effect transistor forms a variable resistor, and the output end of the amplitude control circuit is connected to the first field effect transistor.

[0008] Furthermore, the current-to-voltage conversion circuit includes a second resistor, a second capacitor and a first operational amplifier, one end of the second resistor is connected to the negative input port of the first operational amplifier, and the other end is connected to the output port of the first operational amplifier.

[0009] Furthermore, the comparator circuit includes a second operational amplifier and adopts a zero-crossing comparison circuit, wherein a negative input port of the second operational amplifier is connected to an output port of the first operational amplifier.

[0010] Furthermore, the amplitude control circuit includes a peak detection circuit and an error amplifier circuit, wherein the peak detection circuit is used to detect the peak value of the voltage output by the current-to-voltage conversion circuit, and the error amplifier circuit is used to compare the peak voltage with the reference voltage to generate an error amplification signal, and then generate an amplitude control voltage.

[0011] Furthermore, the field effect transistor of the pulse width modulation generating circuit is a junction field effect transistor or a metal-oxide semi-conductor field effect transistor, wherein the resistance of the field effect transistor can be adjusted by the amplitude control voltage, thereby adjusting the pulse width of the pulse width modulation generating circuit, and further adjusting the signal strength input to the resonant sensor.

[0012] The present invention further provides a method for debugging a closed-loop circuit of a pulse width modulated silicon resonant pressure sensor, the steps comprising:

[0013] Step 1, test the vibration frequency and operating frequency range of the resonator;

[0014] Step 2: Determine the center frequency, vibration amplitude and phase of the resonator to be tested according to the vibration frequency and operating frequency range of the resonator, determine the parameters of the current-voltage conversion circuit according to the center frequency and vibration amplitude, and adjust the amplification strength of the signal of the resonator;

[0015] Step 3: adjusting the height and phase of the pulse width of the signal according to the output signal of the current-voltage conversion circuit so that the phase shift is 0°;

[0016] Step 4: Connect the comparator circuit and the pulse width modulation generating circuit to form a closed-loop system to realize the closed-loop of the sensor.

[0017] Furthermore, the height of the driving signal pulse width is adjusted by adjusting the first capacitor of the pulse width modulation generating circuit, and the loop phase is matched by adjusting the first capacitor of the pulse width modulation generating circuit and the second capacitor of the current-voltage conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A closed-loop circuit framework diagram of a pulse width modulated silicon resonant pressure sensor of the present invention is shown;

[0019] Figure 2 A schematic diagram showing a closed-loop circuit of a pulse width modulated silicon resonant pressure sensor of the present invention;

[0020] Figure 3 A circuit pulse excitation analysis diagram of the present invention is shown;

[0021] Figure 4 A schematic diagram showing a self-stabilizing amplitude control principle of a pulse width modulated silicon resonant pressure sensor closed-loop circuit of the present invention;

[0022] Figure 5 A schematic diagram showing a temperature compensated pulse width modulation closed loop circuit of the present invention;

[0023] Figure numerals: 1-resonant sensor; 2-current-voltage conversion circuit (I / V conversion circuit); 3-comparator circuit; 4-amplitude control circuit; 5-pulse width modulation generation circuit. DETAILED DESCRIPTION

[0024] In order to achieve the above object, the present invention adopts the following technical solution:

[0025] For better explanation, this embodiment is described by taking the electrostatic excitation / capacitive detection resonant pressure sensor as an example, and other types can be adaptively adjusted without affecting the principle. The pulse width modulated silicon resonant pressure sensor closed-loop circuit includes a resonant sensor, a current-to-voltage conversion circuit (I / V conversion circuit), a comparator circuit, an amplitude control circuit and a pulse width modulation generating circuit. Among them, the I / V conversion circuit converts the capacitance change of the resonant vibration into a voltage output, and the comparator circuit converts the amplified frequency signal into a power rail (or a Zener diode voltage) square wave signal, generates a pulse signal through the pulse width modulation generating circuit, and is connected to the driving end of the resonator to generate a driving signal to form a closed-loop system.

[0026] like Figure 1 As shown, the closed-loop circuit framework of the pulse width modulated silicon resonant pressure sensor includes a resonant sensor 1, a current-to-voltage conversion circuit (I / V conversion circuit) 2, a comparator circuit 3, an amplitude control circuit 4 and a pulse width modulation generation circuit 5.

[0027] Among them, firstly, a small signal is transmitted from the resonant sensor 1, and the signal current passes through the I / V conversion circuit 2, converting the signal current into a signal voltage, and amplifying the voltage value, in order to provide a strong signal for the subsequent circuit. The amplified signal is divided into two paths, one path passes through the comparator circuit 3, converting the amplified frequency signal into a square wave signal, which is used as a pulse source for feedback to the resonant sensor 1, and the other path passes through the amplitude control circuit 4, and generates a DC signal after passing through the amplitude detection circuit 4. The DC signal is used for the differential module circuit of the pulse width modulation generation circuit 5, and a pulse signal is generated through the pulse width modulation generation circuit, and input into the driving end of the resonator of the resonant sensor to generate a driving signal. The pulse width modulation generation circuit 5 can adjust the equivalent resistance, thereby controlling the driving signal, and realizing self-stabilizing amplitude control of the gain of the closed-loop circuit.

[0028] Specifically, Figure 2 As shown, Figure 2 The schematic diagram of the closed-loop circuit of the pulse width modulated silicon resonant pressure sensor is shown in FIG. The vibration sensor 1 is an electrostatic excitation / capacitive detection resonant pressure sensor, which includes a resonator, which is connected to the input end of the I / V conversion circuit. The resonator generates a signal current through oscillation, and the signal current is input to the I / V conversion circuit as an input current.

[0029] The I / V conversion circuit includes a resistor, a capacitor and an operational amplifier. One end of the resistor is connected to the negative input port of the operational amplifier, and the other end is connected to the output port of the operational amplifier to achieve negative feedback. The positive input port of the operational amplifier is connected to the ground.

[0030] Resistors are resistors with a current-to-voltage conversion ratio. If the resistor is 1KΩ, it means that there is a 1mA current input, and a 1V signal will be obtained at the output of the operational amplifier, and the current-to-voltage conversion ratio is 1000:1. Operational amplifiers are used to amplify input signals.

[0031] In a further embodiment, a capacitor is connected in parallel with a resistor. The introduction of the capacitor is used to change the frequency characteristics of the circuit and reduce high-frequency noise. When the signal frequency is too high, the junction capacitance and the feedback resistor may oscillate, so the capacitor also plays a role in phase compensation here, and can cooperate with the pulse width modulation differential circuit to fine-tune the phase.

[0032] After the input signal passes through the I / V conversion circuit, the signal strength is amplified to provide a strong signal for the subsequent circuit. The amplified signal is divided into two paths, one is formed into a DC signal through the amplitude detection circuit, and generates a control voltage through the error amplifier circuit, and the other is converted into a square wave signal through the comparator.

[0033] The comparator circuit adopts a zero-crossing comparison circuit. Among them, the negative input port of the operational amplifier in the comparator circuit is connected to the output port of the operational amplifier in the I / V conversion circuit to realize the conversion of sine wave to square wave. The comparator circuit needs to select an operational amplifier chip with higher accuracy, low noise and fast response. In this embodiment, a 3.3V voltage regulator diode is connected after the comparator to generate a square wave signal with a peak value of 3.3V.

[0034] In another embodiment, the square wave may be generated using an op amp hysteresis comparator circuit, a threshold comparison circuit, or a filter circuit.

[0035] Furthermore, the signal amplified by the I / V conversion circuit passes through a peak detection circuit before passing through the amplitude control circuit.

[0036] Furthermore, the peak detection circuit includes a diode and a filter circuit. The diode is used to selectively pass the sine wave signal in one direction, and obtain the highest voltage of the sine wave through the subsequent filter circuit (charging the capacitor) to obtain the peak value. By comparing the peak value with the reference voltage, an amplitude control signal is output.

[0037] The pulse width modulation generating circuit includes a differential module circuit. The DC signal generated after passing through the amplitude control circuit is used in the differential module circuit of the pulse width modulation generating circuit. The pulse signal is generated by the pulse width modulation generating circuit and input into the driving end of the resonator of the resonant sensor to generate a driving signal.

[0038] The differential module circuit includes a capacitor, a resistor and a field effect transistor, wherein one end of the capacitor is connected to the output end of the comparator circuit, the other end is connected to one end of the resistor, the other end of the resistor is connected to the output port of the field effect transistor, the field effect transistor and the capacitor form a series resistor, the gate port of the field effect transistor is connected to the output end of the amplitude detection circuit, and one end of the resistor connected to the capacitor serves as the output end of the pulse width modulation generating circuit and is connected to the resonator of the resonant sensor.

[0039] The field effect transistor uses its own variable resistance area, which is equivalent to a variable resistor. Therefore, the pulse width modulation circuit can achieve the effect of an RC differential circuit, thereby differentiating the square wave signal generated by the comparator to obtain a pulse signal.

[0040] The differential module is a key link in the pulse excitation circuit. After the signal passes through the comparator and is converted from a sine wave to a square wave, it passes through the differential module to generate a pulse waveform.

[0041] The differential module is not only a high-pass filter circuit, but also a differential circuit. The following is an analysis of the module. When the input signal is a square wave, the time domain method is used to obtain its output voltage:

[0042]

[0043] like Figure 3 As shown, when t = t 1 When V I From 0 to V m Since capacitor C cannot be charged instantly (equivalent to short circuit), the voltage on the capacitor remains zero (V C =0), so at this moment the input voltage V I On the resistor R, the output voltage V O Equal to the voltage across the resistor, V O =V R =V I =V m . Then t>>t 1 , the voltage of capacitor C rises exponentially, and the output voltage decreases accordingly (because V O =V I -V C =V m -V C ), after about 3τ (τ = R × C), the capacitor is charged to the same voltage as the input voltage (V = V m ), output voltage V O =0, the smaller the value of the time constant RC, the faster the charging and discharging process, and the narrower the width of the output positive pulse.

[0044] Furthermore, the field effect transistor is a junction field effect transistor (FET).

[0045] Pulse width modulation control: First, the AC signal output by the current-voltage conversion circuit is converted into a DC signal through the amplitude detection circuit. Because the equivalent resistance of FET is different under different feedback DC signals, when the signal strength increases, the control voltage becomes larger, and the equivalent resistance of the FET tube decreases, resulting in a decrease in the output pulse signal pulse width, achieving the effect of reducing the drive, thereby realizing self-stabilizing amplitude control of the pulse circuit.

[0046] Combination Figure 2 and Figure 4 , when the resonator output signal decreases due to environmental changes and other factors, that is, U i The decrease leads to a decrease in the DC signal output by the amplitude detection circuit, that is, U p Then the gate-source voltage decreases, that is, U GS decreases, that is, the equivalent resistance of the FET tube increases, that is, R j Increase, the differential module outputs the pulse signal acting on the resonator to increase U o Increase, thus enhancing the resonator output signal to achieve self-stabilizing amplitude control.

[0047] Furthermore, the field effect transistor may also be a metal-oxide-semiconductor field effect transistor (MOSFET).

[0048] Another embodiment of this solution is as follows Figure 5 As shown, Figure 5 The following is a schematic diagram of a temperature compensated pulse width modulation closed-loop circuit. To further simplify the circuit architecture, the closed-loop circuit consists of a current-to-voltage conversion circuit, a comparator circuit, and a differential circuit. The resonator is excited by a constant pulse width signal, and the amplitude of the resonator is not controlled.

[0049] Considering that the amplitude of the resonator is affected by temperature, the amplitude of the resonator usually decreases as the temperature increases. Therefore, in this embodiment, in order to compensate for the decrease in the driving signal, a thermistor is used to replace the field effect tube in the first embodiment to form a differential circuit for pulse width modulation. Specifically, a positive temperature coefficient thermistor (PTC) is used. When the temperature increases, the resistance increases, the pulse width of the driving signal becomes wider, and the driving signal increases, thereby compensating for the attenuation of the resonator signal.

[0050] The present invention also provides a pulse width modulated silicon resonant pressure sensor closed-loop circuit debugging method, comprising the following steps:

[0051] Step 1: Test the vibration frequency and operating frequency range of the resonator.

[0052] Specifically, an open-loop test is performed on the resonator using equipment such as a network analyzer to determine its center frequency and operating frequency range.

[0053] Step 2: Determine the center frequency and frequency variation range of the resonator, and determine the current-to-voltage conversion circuit parameters based on the frequency, so that the resonator output signal strength reaches more than 100mV and can be used for square wave conversion.

[0054] Step 3: Adjust the height and phase of the signal pulse width.

[0055] Specifically, the comparator circuit output of the circuit is disconnected and connected to a signal generator to generate a square wave signal of the resonator frequency. The signal is passed through a pulse width modulation generating circuit, a resonator, an I / V conversion circuit, an amplitude control circuit and a comparator circuit. Finally, the comparator circuit outputs a square wave signal, and an oscilloscope, a signal analyzer and other equipment are used to perform phase analysis on the signal generator signal and the output signal. Near-zero phase shift is achieved by adjusting circuit parameters such as the I / V conversion circuit and the differential circuit.

[0056] Specifically, by adjusting the resistance of the pulse width generating circuit, the pulse width height and phase can be adjusted. By adjusting the parallel capacitor of the I / V conversion circuit, the pulse width output circuit signal attenuation and phase shift can be compensated, thereby meeting the closed-loop gain condition.

[0057] Step 4: The output of the comparator circuit is connected to the pulse width generating circuit to form a closed-loop system to realize the closed-loop of the sensor.

[0058] The advantages of the present invention are:

[0059] (1) This design adopts the pulse excitation method. Compared with sinusoidal excitation, the initial voltage signal of pulse excitation is larger and the driving force is stronger. When the resonator is at the maximum amplitude, the driving force drops to 0, which can achieve a larger amplitude while avoiding the potential influence of electrostatic attraction, thereby improving the signal-to-noise ratio of the sensor during operation and ensuring the reliability of the resonant sensor.

[0060] (2) The closed-loop drive circuit designed in this paper adopts a pulse excitation scheme. A new self-stabilizing amplitude control scheme is studied, which acts on the FET tube to change its equivalent resistance to achieve self-stabilizing amplitude control. This scheme can ensure that the amplitude of the control resonator is maintained within a suitable range, thereby improving the stability of the resonant sensor;

[0061] (3) Compared with other circuits, the circuit structure of this design is simpler and uses fewer op amp chips. Therefore, the noise introduced by components will be less.

[0062] (4) By utilizing the high slew rate characteristics of the comparator, a small-amplitude signal can be quickly converted into a square wave signal, and at the same time converted into a pulse signal through a differential circuit. Due to the large energy of the pulse excitation signal in a very short time, compared with the continuous action of the traditional sinusoidal excitation, its startup time is shorter at a larger energy, meeting the fast startup and fast response characteristics in the fields of industrial control and aerospace.

Claims

1. A pulse width modulated silicon resonant pressure sensor closed-loop circuit, comprising a resonant sensor, a current-to-voltage conversion circuit, a comparator circuit, an amplitude control circuit and a pulse width modulation generating circuit, wherein the output end of the resonant sensor is connected to the input end of the current-to-voltage conversion circuit, the output end of the current-to-voltage conversion circuit is respectively connected to the input end of the comparator circuit and the input end of the amplitude control circuit, the output end of the comparator circuit is connected to the input end of the pulse width modulation generating circuit, and the output end of the pulse width modulation generating circuit is connected to the input end of the resonant sensor, wherein: The pulse width modulation generating circuit includes a first capacitor, a first resistor and a first field effect transistor. The first field effect transistor forms a variable resistor. The output end of the amplitude control circuit is connected to the first field effect transistor.

2. According to the pulse width modulated silicon resonant pressure sensor closed-loop circuit of claim 1, the current-to-voltage conversion circuit includes a second resistor, a second capacitor and a first operational amplifier, one end of the second resistor is connected to the negative input port of the first operational amplifier, and the other end is connected to the output port of the first operational amplifier.

3. According to the pulse width modulated silicon resonant pressure sensor closed-loop circuit of claims 1 and 2, the comparator circuit comprises a second operational amplifier and adopts a zero-crossing comparison circuit, wherein: A negative input port of the second operational amplifier is connected to an output port of the first operational amplifier.

4. According to the pulse width modulated silicon resonant pressure sensor closed-loop circuit described in claim 1, the amplitude control circuit includes a peak detection circuit and an error amplifier circuit, wherein the peak detection circuit is used to detect the peak value of the voltage output by the current-to-voltage conversion circuit, and the error amplifier circuit is used to compare the peak voltage with the reference voltage to generate an error amplification signal, and then generate an amplitude control voltage.

5. According to the pulse width modulated silicon resonant pressure sensor closed-loop circuit of claim 1, the field effect transistor of the pulse width modulation generating circuit is a junction field effect transistor or a metal-oxide semi-conductor field effect transistor, wherein the resistance of the field effect transistor can be adjusted by the amplitude control voltage, thereby adjusting the pulse width of the pulse width modulation generating circuit, and further adjusting the signal strength input to the resonant sensor.

6. A method for debugging a closed-loop circuit of a pulse width modulated silicon resonant pressure sensor, characterized in that: The debugging method comprises the following steps: Step 1, test the vibration frequency and operating frequency range of the resonator; Step 2: Determine the center frequency, vibration amplitude and phase of the resonator to be tested according to the vibration frequency and operating frequency range of the resonator, determine the parameters of the current-to-voltage conversion circuit according to the center frequency and the vibration amplitude, and adjust the amplification strength of the signal of the resonator; Step 3, adjusting the pulse width and phase of the signal according to the output signal of the current-voltage conversion circuit so that the phase shift is 0°; Step 4: Connect the comparator circuit and the pulse width modulation generating circuit to form a closed-loop system to realize the closed-loop of the sensor.

7. The debugging method of the pulse width modulated silicon resonant pressure sensor closed-loop circuit according to claim 6, characterized in that: The height of the driving signal pulse width is adjusted by adjusting the first capacitor of the pulse width modulation generating circuit, and the loop phase is matched by adjusting the first capacitor of the pulse width modulation generating circuit and the second capacitor of the current-voltage conversion circuit.

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