A synchronous measurement system for natural frequency and quality factor of microresonator

Abstract

The present invention discloses a synchronous measurement system for the natural frequency and quality factor of a micro-resonator, which is used to control the on and off of an electric control switch through an FPGA for measurement. When the first input end of the switch is closed, the resonator driving electrode is connected to the AGC output end, and the C / V interface detection circuit and the AGC form a closed-loop driving circuit, so that the resonator works at a stable amplitude; when the second input end of the switch is closed, the resonator driving electrode is grounded, the driving circuit is open-loop, and the resonator amplitude is attenuated. During the attenuation process, the signal is collected by a comparator; the positive ends of the two comparators are connected to the output end of the C / V interface detection circuit, and the negative ends are provided with different threshold voltages, which are used to convert the detection signal into a square wave signal and input it into the FPGA; the FPGA calculates and outputs the natural frequency and quality factor according to the square wave signal. The present invention is characterized in that the synchronous reading of the natural frequency and the quality factor can be completed only by the comparator and the FPGA, and the test cost is low and the operation is simple.

Description

Technical Field

[0001] The invention belongs to the field of resonant sensors, in particular to a micro-resonator natural frequency and quality factor synchronous measurement system. Background Art

[0002] With the rapid development of MEMS (Micro-Electro-Mechanical System) technology, micro-resonators have gradually become a research hotspot, which has greatly improved the technology of micro-resonant sensors. Compared with other types of sensors, micro-resonant sensors use micro-resonators as sensitive units, which have significant advantages such as small size, light weight, compact structure, high resolution, and strong anti-interference ability. Based on MEMS technology, micro-resonators can convert changes in the measured parameters into changes in their own parameters. Among them, the natural frequency and quality factor of the micro-resonator have important physical significance in the sensor measurement process. For example, in a resonant acceleration sensor, the natural frequency of the resonator can be used to characterize acceleration, and the quality factor of the resonator can be used for temperature compensation; in a resonant pressure sensor, the quality factor of the resonator can be used to characterize pressure; in a resonant gyroscope, the natural frequency of the resonator can be used to characterize temperature. Therefore, whether the natural frequency and quality factor of the resonator can be accurately and real-time extracted is directly related to the measurement accuracy of the resonant sensor.

[0003] Measuring the natural frequency of a micro-resonator is relatively simple. First, the resonator starts to resonate under the action of a closed-loop drive circuit. At this time, the frequency of the detection signal in the circuit is the natural frequency of the resonator, and the detection signal is a sine wave signal, which can be converted into a digital signal through a simple conversion to find its frequency. The quality factor measurement of a resonant sensor is more complicated. The quality factor of a resonant sensor, also known as the Q value, is used to characterize the damping properties of the resonator oscillator. Chinese patent CN110553666 A discloses a method for obtaining the quality factor of a MEMS gyroscope. First, a signal generator is connected to the input end of the gyroscope open-loop drive circuit, and an oscilloscope is connected to the output end of the drive circuit. The signal generator sends a test signal according to the natural frequency of the gyroscope. At this time, the peak value of the output signal of the drive circuit is linearly related to the amplitude of the resonator. The oscilloscope is set to collect the output of the drive circuit at a higher sampling rate, and the decay time constant of the output signal is calculated to calculate the quality factor. This method is not only cumbersome to operate, but also requires too many measuring equipment and the testing cost is too high. Summary of the invention

[0004] The object of the present invention is to provide a micro-resonator natural frequency and quality factor synchronous measurement system, which can realize the synchronous extraction and output of the micro-resonator natural frequency and quality factor without the aid of an analog-to-digital converter and a host computer.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A micro-resonator natural frequency and quality factor synchronous measurement system, comprising a C / V interface detection circuit, an automatic gain control circuit AGC, an electric control switch, a first comparator, a second comparator, and a field programmable gate array FPGA;

[0007] The input end of the C / V interface detection circuit is connected to the detection electrode of the micro-resonator, and the detection current signal I obtained by the resonator detection electrode is s Converted into detection signal V s The automatic gain control circuit AGC is connected to the output end of the C / V interface detection circuit to control the detection signal V s The amplitude of the output drive signal V d The first input terminal S1 of the electric control switch is connected to the output terminal of the automatic gain control circuit, the second input terminal S2 is grounded, and the output terminal is connected to the driving electrode of the resonator, which is used to switch the vibration mode of the micro-resonator; the two comparator input terminals are connected to the output terminal of the C / V interface detection circuit, which is used to collect the detection signal V s The two comparator output ends are connected to the field programmable gate array FPGA; the field programmable gate array FPGA and the electric control switch are used to control the on and off of the electric control switch; when the first input end S1 of the electric control switch is closed and the second input end S2 is disconnected, the output end of the automatic gain control circuit is connected to the micro-resonator driving electrode to form a closed-loop driving circuit, and the driving signal V d The micro-resonator is driven to operate at a stable amplitude; when the first input terminal S1 of the electric control switch is disconnected and the second input terminal S2 is closed, the micro-resonator driving electrode is grounded, the resonator enters a free oscillation mode, the amplitude gradually decays, and the field programmable gate array FPGA begins to synchronously measure the natural frequency and quality factor of the micro-resonator.

[0008] Compared with the prior art, the present invention has the following significant advantages:

[0009] (1) Compared with the traditional method of using an analog-to-digital converter (ADC) for data acquisition, the microresonator natural frequency and quality factor measurement system of the present invention directly converts the analog signal containing frequency information and quality factor information into a digital signal for processing through two comparators with a given threshold, which has a lower test cost and does not have the quantization error inherent in the analog-to-digital converter (ADC) acquisition.

[0010] (2) Compared with the traditional method of transmitting the collected information to the host computer software for calculation and then obtaining the results, the microresonator natural frequency and quality factor measurement system of the present invention uses FPGA to directly calculate the natural frequency and quality factor of the microresonator and output them through the serial port, which simplifies the test steps and has a higher degree of automation.

[0011] (3) Compared with the traditional method of manually controlling the on and off of the closed-loop circuit for data collection, the resonant sensor natural frequency and quality factor measurement system of the present invention uses FPGA to automatically control the on and off of the closed-loop drive circuit. Each on and off process can output a set of frequency and quality factor data, ensuring the real-time and accuracy of the data, and the output rate can reach more than 100 Hz. The higher output rate also eliminates the need for cumbersome test operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a block diagram of the resonator natural frequency and quality factor measurement system of the present invention.

[0013] Figure 2 It is a schematic diagram of comparator signal acquisition of the present invention.

[0014] Figure 3 This is a schematic diagram of the switch control module of the present invention controlling the resonator to switch vibration modes. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0016] Combination Figure 1 , the present invention is a micro-resonator natural frequency and quality factor synchronous measurement system, including a C / V interface detection circuit, an automatic gain control circuit AGC, an electric control switch, a first comparator, a second comparator, and a field programmable gate array FPGA;

[0017] The input end of the C / V interface detection circuit is connected to the detection electrode of the micro-resonator, and the detection current signal I obtained by the resonator detection electrode is s Converted into detection signal V s The automatic gain control circuit AGC is connected to the output end of the C / V interface detection circuit to control the detection signal V s The amplitude of the output drive signal V d The first input terminal S1 of the electric control switch is connected to the output terminal of the automatic gain control circuit, the second input terminal S2 is grounded, and the output terminal is connected to the driving electrode of the resonator, which is used to switch the vibration mode of the micro-resonator; the two comparator input terminals are connected to the output terminal of the C / V interface detection circuit, which is used to collect the detection signal V s The two comparator output ends are connected to a field programmable gate array FPGA, and the field programmable gate array FPGA is used to realize the synchronous measurement of the natural frequency and quality factor of the microresonator.

[0018] Furthermore, the automatic gain control circuit AGC comprises a full-wave rectifier circuit, a low-pass filter circuit, a PI control circuit, and a multiplier connected in sequence;

[0019] The full-wave rectifier circuit is connected to the C / V interface detection circuit to convert the detection signal V s The negative half-cycle signal is converted into a positive half-cycle signal;

[0020] The low-pass filter circuit is used to perform low-pass filtering on the output signal of the full-wave rectifier circuit to extract the amplitude of the detection signal;

[0021] The PI control circuit is used to compare the amplitude extracted by the low-pass filter circuit with the reference voltage V ref The comparison is performed and the difference is integrated to output a DC gain signal V g ;

[0022] The multiplier is connected to the first input terminal S1 of the electronically controlled switch and is used to convert the DC gain signal V output by the PI control circuit into g With the detection signal V s Multiply them to get the driving voltage signal V d , output to the driving electrode of the microresonator, driving the microresonator to vibrate.

[0023] When the detection signal V s The amplitude is less than the reference voltage V ref When the automatic gain control circuit outputs the drive signal V d becomes larger, the vibration amplitude of the resonator becomes larger, making the detection current signal I obtained by the resonator detection electrode s becomes larger, thereby increasing the detection signal V s The amplitude of the detection signal V s The amplitude is greater than the reference voltage V ref When the automatic gain control circuit outputs the drive signal V d becomes smaller, the vibration amplitude of the resonator becomes smaller, making the detection current signal I obtained by the resonator detection electrode s becomes smaller, thereby reducing the detection signal V s After a period of stabilization, the detection signal V s The amplitude will be different from the reference voltage V ref The microresonator will vibrate at its own natural frequency while maintaining a fixed amplitude. s The frequency is the same as the natural frequency of the resonator, and the detection signal V s The amplitude of the resonator directly reflects the amplitude of the resonator. When calculating the natural frequency and quality factor of the resonator, the detection signal V s The frequency represents the natural frequency of the resonator, and the detection signal V s The amplitude decay rate characterizes the decay rate of the resonator amplitude.

[0024] Furthermore, the electronically controlled switch is a single-pole double-throw switch controlled by an FPGA. When the first input terminal S1 of the electronically controlled switch is closed and the second input terminal S2 is disconnected, the output terminal of the automatic gain control circuit is connected to the micro-resonator driving electrode to form a closed-loop driving circuit, and the driving signal V d The microresonator is driven to operate at a stable amplitude; when the first input terminal S1 of the electric control switch is disconnected and the second input terminal S2 is closed, the microresonator driving electrode is grounded, the resonator enters a free oscillation mode, and the amplitude gradually decays.

[0025] Furthermore, the first comparator and the second comparator are used to collect the detection signal V s , convert it into a digital signal and send it to FPGA for processing. The positive input of the first comparator and the second comparator are both detection signals V s The negative inputs of the first comparator and the second comparator are the upper threshold voltage V th1 and the lower threshold voltage V th2 , the outputs are square wave signals V b1 、V b2 When the comparator's positive input voltage is greater than the negative input voltage, the comparator outputs a high level; when the comparator's positive input voltage is less than the negative input voltage, the comparator outputs a low level. The set upper threshold voltage V th1 , lower threshold voltage V th2 According to the detection voltage V s The maximum amplitude is determined by, for example, the upper threshold voltage V th1 Can be set to detect voltage V s 80% of the amplitude, signal lower threshold voltage V th2 Can be set as the detection voltage V s 20% of the amplitude.

[0026] When the electronically controlled switch S1 is open and S2 is closed, the detection signal V s The frequency remains unchanged, and the amplitude begins to decay. At this time, the detection signal V s The natural frequency and quality factor of the microresonator are extracted from the microresonator. In this stage, two comparators detect the signal V s The specific collection process is as follows Figure 2 As shown, it is mainly divided into the following three stages:

[0027] (a) Detection signal V s The peak value is greater than the upper threshold voltage V th1 ,like Figure 2 From t0 to t1: In each detection signal cycle of this stage, the positive terminals of the two comparators detect the signal V sThe voltage is first smaller than the negative reference voltage, then larger than the negative reference voltage, and finally smaller than the negative reference voltage. Therefore, the comparator outputs low level, high level, and low level in each cycle, which is a square wave signal. s The peak value of the comparator positive terminal voltage is smaller and smaller, and the time when the comparator positive terminal voltage is greater than the negative terminal voltage is shorter and shorter, so the square wave signal V b1 、V b2 The medium and high level time is also getting shorter and shorter, that is, the signal duty cycle is getting smaller and smaller;

[0028] (b) Detection signal V s The peak value is greater than the lower threshold voltage V th2 and is less than the upper threshold voltage V th1 ,like Figure 2 From t1 to t2 in the process: in each detection signal cycle of this phase, the positive input voltage of the first comparator is always less than the negative input voltage, so the output is a constant low level; the state of the second comparator is still the same as that of phase (a), and the output is a square wave signal with a gradually decreasing duty cycle;

[0029] (c) Detection signal V s The peak value is less than the lower threshold voltage V th2 ,like Figure 2 The stage after t2: In each detection signal cycle of this stage, the positive input voltage of the two comparators is always smaller than the negative input voltage, so both comparators output a constant low level.

[0030] Furthermore, the field programmable gate array FPGA includes a switch control module, a first counter, a second counter, a third counter, a natural frequency readout module, a quality factor readout module, and a serial port output module;

[0031] The switch control module controls the on and off of the electronically controlled switch by outputting high and low levels, and controls three counters to collect the output signals of the two comparators and the clock signal. The control signal is in the form of a square wave. When the switch control module outputs a high level, that is, Figure 3 At time T1 in the figure, the switch output terminal D is connected to the first switch input terminal S1, and the drive signal V output by the amplitude control circuit is d It is connected to the driving electrode of the resonator to form a feedback drive loop. After a period of stability, the resonator vibrates at its own natural frequency and maintains a fixed amplitude. At this time, the three counters are closed and do not count. When the switch control module outputs a high level, that is, Figure 3At time T2 in the circuit, the switch output terminal D is connected to the second switch input terminal S2, the driving electrode of the resonator is grounded, the driving circuit is open-loop, and the resonator enters a free oscillation state. Due to the existence of damping, the amplitude of the resonator begins to gradually decay. In this stage, the switch control module controls three counters to collect the output signals of the two comparators and the clock signal. After the collection is completed, the switch control module outputs a high level again to make the resonator re-enter the forced vibration state, and so on.

[0032] The switch control module controls the on and off of the electronically controlled switch by outputting high and low levels, and controls three counters to collect the output signals of the two comparators and the clock signal.

[0033] The first timer input terminal is connected to the first comparator output terminal, and the square wave signal V output by the first comparator is captured. b1 The rising edge of the first comparator counts the number of square waves output by the first comparator;

[0034] The second timer input terminal is connected to the second comparator output terminal, and the second comparator square wave signal V is captured. b2 The rising edge of the second comparator counts the number of square waves output by the second comparator;

[0035] The third timer inputs a standard clock signal and counts the number of square waves of the clock signal by capturing the rising edge of the clock signal;

[0036] When the electronically controlled switch S1 is disconnected and S2 is closed, and the detection signal begins to decay, the three timers start counting at the same time. When the first comparator outputs a constant low level, the first counter stops counting, and the count value is recorded as N1; when the second comparator outputs a constant low level, the second counter and the third counter stop counting, and the count values ​​are recorded as N2 and N3 respectively. r ;

[0037] The natural frequency reading module calculates the natural frequency of the resonator according to the count values ​​output by the second counter and the third counter;

[0038] The specific process is as follows: The natural frequency of the microresonator and the detection signal V s The frequency is the same as that of the detection signal V s The frequency of the micro-resonator can be obtained. From the above, it can be seen that the second counter and the third counter start counting at the same time and end counting at the same time. The second counter collects the square wave signal V b1 The number of detection signals V s Same frequency; the third counter collects the number of clock signals, the clock frequency f r Known, therefore, the natural frequency f0 can be obtained by the following formula:

[0039]

[0040] The quality factor reading module calculates the quality factor of the resonator according to the count values ​​output by the first counter and the second counter;

[0041] The specific process is as follows: According to the definition, the quality factor Q of the resonator is usually calculated using the following formula:

[0042]

[0043] In the formula, ω n represents the natural frequency of the resonator, and k represents the resonator amplitude attenuation rate. From the above acquisition stage, it can be seen that when the detection signal V s The peak voltage is from the upper threshold voltage V th1 Drop to the lower threshold voltage V th2 During this time t, the FPGA collected a total of (N2-N1) square waves, and the square wave has the same frequency as the detection signal, so this time t can be calculated by the following formula:

[0044]

[0045] Therefore, the resonator amplitude decay rate can be given by:

[0046]

[0047] Substituting equations (1) and (4) into equation (2), we can obtain:

[0048]

[0049] Therefore, the natural frequency and quality factor of the microresonator can be obtained by equations (1) and (5). By implementing the calculation process of equation (1) in the FPGA natural frequency readout module, the corresponding natural frequency can be obtained; by implementing the calculation process of equation (5) in the FPGA quality factor readout module, the corresponding quality factor can be obtained.

[0050] The serial port output module is connected to the output ends of the natural frequency readout module and the quality factor readout module, and outputs the natural frequency and quality factor calculated by the natural frequency readout module and the quality factor readout module in real time through the serial port.

[0051] Furthermore, the above scheme can collect and calculate a set of natural frequency and quality factor data in each set of switch on and off processes, and the two parameters are collected simultaneously in the same free vibration process, ensuring the real-time and accuracy of the data.

Claims

1. A microresonator natural frequency and quality factor synchronous measurement system, characterized in that: It includes a C / V interface detection circuit, an automatic gain control circuit AGC, an electric control switch, a first comparator, a second comparator, and a field programmable gate array FPGA; The input end of the C / V interface detection circuit is connected to the detection electrode of the micro-resonator, and the detection current signal I obtained by the resonator detection electrode is s Converted into detection signal V s The automatic gain control circuit AGC is connected to the output end of the C / V interface detection circuit to control the detection signal V s The amplitude of the output drive signal V d The first input terminal S1 of the electric control switch is connected to the output terminal of the automatic gain control circuit, the second input terminal S2 is grounded, and the output terminal is connected to the driving electrode of the resonator, which is used to switch the vibration mode of the micro-resonator; the two comparator input terminals are connected to the output terminal of the C / V interface detection circuit, which is used to collect the detection signal V s ; The output ends of the two comparators are connected to the field programmable gate array FPGA; the on and off of the electric control switch is controlled by the field programmable gate array FPGA; When the first input terminal S1 of the electric control switch is closed and the second input terminal S2 is disconnected, the output terminal of the automatic gain control circuit is connected to the micro-resonator driving electrode to form a closed-loop driving circuit. d Driving the microresonator to operate at a stable amplitude; When the first input terminal S1 of the electric control switch is disconnected and the second input terminal S2 is closed, the micro-resonator driving electrode is grounded, the resonator enters a free oscillation mode, the amplitude gradually decays, and the field programmable gate array FPGA begins to synchronously measure and output the natural frequency and quality factor of the micro-resonator.

2. The measuring system according to claim 1, characterized in that The automatic gain control circuit AGC comprises a full-wave rectifier circuit, a low-pass filter circuit, a PI control circuit, and a multiplier connected in sequence; The full-wave rectifier circuit is connected to the C / V interface detection circuit to convert the detection signal V s The negative half-cycle signal is converted into a positive half-cycle signal; The low-pass filter circuit is used to perform low-pass filtering on the output signal of the full-wave rectifier circuit to extract the amplitude of the detection signal; The PI control circuit is used to compare the amplitude extracted by the low-pass filter circuit with the reference voltage V ref The comparison is performed and the difference is integrated to output a DC gain signal V g ; The multiplier is connected to the first input terminal S1 of the electronically controlled switch and is used to convert the DC gain signal V output by the PI control circuit into g With the detection signal V s Multiply them to get the driving voltage signal V d , output to the driving electrode of the microresonator, driving the microresonator to vibrate.

3. The measuring system according to claim 1, characterized in that The two comparators collect the detection signal V s The process is as follows: the positive inputs of the two comparators are both detection signals V s , and its negative input is the upper threshold voltage V th1 and the lower threshold voltage V th2 , and its outputs are square wave signals V b1 、V b2 ; When the positive input voltage of the comparator is greater than the negative input voltage, the comparator outputs a high level; when the positive input voltage of the comparator is less than the negative input voltage, the comparator outputs a low level; specifically, it can be divided into the following three processes: (a) When the detection signal V s The peak value is greater than the upper threshold voltage V th1 In this stage, in each detection signal cycle, the positive detection signal V s The voltage is first smaller than the negative reference voltage, then larger than the negative reference voltage, and finally smaller than the negative reference voltage. s The peak value of is getting smaller and smaller, and the time during which the positive terminal voltage of the comparator is greater than the negative terminal voltage is getting shorter and shorter. Therefore, both comparators output square wave signals with gradually decreasing duty cycle. (b) When the detection signal V s The peak value is greater than the lower threshold voltage V th2 and is less than the upper threshold voltage V th1 In this stage, in each detection signal cycle, the positive input voltage of the first comparator is always less than the negative input voltage, and the output is a constant low level; the state of the second comparator is still the same as in stage (a), and the output is a square wave signal with a gradually decreasing duty cycle; (c) When the detection signal V s The peak value is less than the lower threshold voltage V th2 During each detection signal cycle of this stage, the positive input voltage of the two comparators is always less than the negative input voltage, and both comparators output a constant low level.

4. The measuring system according to claim 1, characterized in that The field programmable gate array FPGA includes a switch control module, a first counter, a second counter, a third counter, a natural frequency readout module, a quality factor readout module, and a serial port output module; The switch control module controls the on and off of the electronically controlled switch by outputting high and low levels, and controls three counters to collect the output signals of the two comparators and the clock signal. The first counter input terminal is connected to the first comparator output terminal, and the square wave signal V output by the first comparator is captured. b1 The rising edge of the first comparator counts the number of square waves output by the first comparator; The second counter input terminal is connected to the second comparator output terminal, and the second comparator square wave signal V is captured. b2 The rising edge of the second comparator counts the number of square waves output by the second comparator; The third counter inputs a standard clock signal, and counts the number of square waves of the clock signal by capturing the rising edge of the clock signal; The natural frequency reading module is used to calculate the natural frequency of the resonator according to the count values ​​output by the second counter and the third counter; The quality factor reading module is used to calculate the quality factor of the resonator according to the count values ​​output by the first counter and the second counter; The serial port output module is connected to the output ends of the natural frequency readout module and the quality factor readout module, and outputs the natural frequency and quality factor calculated by the natural frequency readout module and the quality factor readout module in real time through the serial port.

5. The measuring system according to claim 4, characterized in that The process of calculating the natural frequency of the resonator by the natural frequency readout module is as follows: Natural frequency f0: where f r is the standard clock signal frequency, N2 and N r are the count values ​​of the second counter and the third counter respectively.

6. The measuring system according to claim 4, characterized in that The process of calculating the quality factor of the resonator by the quality factor readout module is: Quality factor Q: where ω n represents the natural frequency of the resonator, k represents the amplitude attenuation rate of the resonator; when the detection signal V s The peak voltage is from the upper threshold voltage V th1 Drop to the lower threshold voltage V th2 During this time t, FPGA collected a total of (N2-N1) square waves. This time t is: Resonator amplitude decay rate k: Substituting equations (1) and (4) into equation (2), we obtain:

7. The measuring system according to claim 1, characterized in that The electric control switch is a single-pole double-throw switch.

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