CN212134821U - Micro-resonator natural frequency and quality factor synchronous measurement system - Google Patents
Micro-resonator natural frequency and quality factor synchronous measurement system Download PDFInfo
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- CN212134821U CN212134821U CN202020163468.3U CN202020163468U CN212134821U CN 212134821 U CN212134821 U CN 212134821U CN 202020163468 U CN202020163468 U CN 202020163468U CN 212134821 U CN212134821 U CN 212134821U
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Abstract
The utility model discloses a synchronous measurement system of microresonator natural frequency and figure of merit, break-make through FPGA control electric control switch is in order to measure. When the first input end of the switch is closed, the driving electrode of the resonator is connected with the output end of the AGC, 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 driving electrode of the resonator is grounded, the driving circuit is opened, the amplitude of the resonator is attenuated, and the comparator finishes signal acquisition in the attenuation process; the positive ends of the two comparators are connected with the output end of the C/V interface detection circuit, and the negative ends of the two comparators are provided with different threshold voltages and are used for converting detection signals into square wave signals to be input into the FPGA; and the FPGA calculates and outputs natural frequency and quality factor according to the square wave signal. The utility model discloses only can accomplish the synchronous reading out of natural frequency and quality factor through comparator and FPGA, the test cost is low and easy operation.
Description
Technical Field
The utility model belongs to resonant mode sensor field, especially a micro resonator natural frequency and quality factor synchronous measurement system.
Background
With the rapid development of the MEMS (Micro-Electro-Mechanical System) technology, the Micro resonator gradually becomes a research hotspot, so that the Micro resonant sensor technology is greatly improved. Compared with other types of sensors, the micro-resonance type sensor takes the micro-resonator as a sensitive unit, and has the remarkable advantages of small volume, light weight, compact structure, high resolution, strong anti-interference capability and the like. The micro-resonator is based on MEMS technology, and can convert the parameter change to be measured into the parameter change of the micro-resonator. Among them, the natural frequency and the 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 the 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 the pressure; in a resonant gyroscope, the natural frequency of the resonator can be used to characterize temperature. Therefore, whether the natural frequency and the quality factor of the resonator can be accurately extracted in real time or not is directly related to the measurement accuracy of the resonant sensor.
It is relatively simple to measure the natural frequency of the microresonator. The resonator is first made to start resonance under the action of closed loop driving circuit, and the frequency of the detected signal in the circuit is the natural frequency of the resonator while the detected signal is sine wave signal and may be converted into digital signal through simple conversion to find its frequency. The quality factor measurement of the resonant sensor is complicated. The quality factor of the resonant sensor, also called Q-value, is used to characterize the damping properties of the resonator element. Chinese patent CN110553666A discloses a method for obtaining quality factor of MEMS gyroscope. Firstly, a signal generator is connected to the input end of a gyroscope open-loop driving circuit, an oscilloscope is connected to the output end of the driving circuit, the signal generator sends out a test signal according to the natural frequency of a gyroscope, at the moment, the peak value of the output signal of the driving circuit is linearly related to the amplitude of a resonator, the oscilloscope is set to collect the output of the driving circuit at a higher sampling rate, and the attenuation time constant of the output signal is calculated, so that the quality factor is calculated. The method is not only complicated to operate, but also needs too many measuring devices and has high testing cost.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide a synchronous measurement system of microresonator natural frequency and figure of merit under the condition of not with the help of adc and host computer, realizes that the synchronization of microresonator natural frequency and figure of merit draws and output.
Realize the utility model discloses the technical solution of purpose does:
a synchronous measurement system for the natural frequency and the quality factor of a micro-resonator comprises 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 with the detection electrode of the micro-resonator, and the detection current signal I acquired by the detection electrode of the micro-resonatorsConverted into a detection signal Vs(ii) a The AGC circuit is connected with the output end of the C/V interface detection circuit and is used for controlling a detection signal VsAnd outputs a drive signal Vd(ii) a The first input end S1 of the electric control switch is connected with the output end of the automatic gain control circuit, the second input end S2 is grounded, and the output end is connected with the driving electrode of the resonator and is used for switching the vibration mode of the micro-resonator; the input ends of the two comparators are connected with the output end of the C/V interface detection circuit and used for collecting a detection signal Vs(ii) a The output ends of the two comparators are connected with a field programmable gate array FPGA; the field programmable gate array FPGA and the electric control switch are used for controlling the on-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 open, the output end of the automatic gain control circuit and the micro-resonanceThe driving electrodes of the driving circuit are connected to form a closed-loop driving circuit, and a driving signal VdDriving the microresonator to operate at a stable amplitude; when the first input end S1 of the electric control switch is disconnected and the second input end S2 is closed, the driving electrode of the micro resonator is grounded, the resonator enters a free oscillation mode, the amplitude is gradually attenuated, and the field programmable gate array FPGA starts to synchronously measure the natural frequency and the quality factor of the micro resonator.
Compared with the prior art, the utility model, it is showing the advantage and is:
(1) use analog to digital converter ADC to carry out data acquisition in with traditional approach and compare, the utility model discloses a microresonator natural frequency and quality factor measurement system are directly will contain the analog signal conversion of frequency information and quality factor information to digital signal through two comparators that are equipped with given threshold value and are handled, and testing cost is lower, and inherent quantization error when not having analog to digital converter ADC to gather.
(2) Carry in the information collection carries host computer software to calculate among the traditional method and reachs the result again and compare, the utility model discloses a microresonator natural frequency and quality factor measurement system adopt FPGA to directly calculate microresonator natural frequency and quality factor and through serial ports output, have simplified the test procedure, and degree of automation is higher.
(3) Compare in order to gather with manual control closed loop break-make among the traditional approach, the utility model discloses a resonant transducer natural frequency and quality factor measurement system adopt FPGA to come automatic control closed loop drive circuit's break-make, and the break-make process can output a set of frequency and quality factor data each time, has guaranteed the real-time and the accuracy of data, and the output rate can reach more than 100Hz, has still removed loaded down with trivial details test operation from when the output rate is higher.
Drawings
Fig. 1 is a block diagram of the system for measuring the natural frequency and the quality factor of the resonator according to the present invention.
Fig. 2 is a schematic diagram of the signal acquisition of the comparator of the present invention.
Fig. 3 is a schematic diagram of the switch control module controlling the resonator to switch the vibration mode.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific embodiments.
With reference to fig. 1, the present invention is a synchronous measurement system for natural frequency and quality factor of micro-resonator, which comprises 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 with the detection electrode of the micro-resonator, and the detection current signal I acquired by the detection electrode of the micro-resonatorsConverted into a detection signal Vs(ii) a The AGC circuit is connected with the output end of the C/V interface detection circuit and is used for controlling a detection signal VsAnd outputs a drive signal Vd(ii) a The first input end S1 of the electric control switch is connected with the output end of the automatic gain control circuit, the second input end S2 is grounded, and the output end is connected with the driving electrode of the resonator and is used for switching the vibration mode of the micro-resonator; the input ends of the two comparators are connected with the output end of the C/V interface detection circuit and used for collecting a detection signal Vs(ii) a The output ends of the two comparators are connected with a field programmable gate array FPGA, and the field programmable gate array FPGA is used for realizing synchronous measurement of the natural frequency and the quality factor of the micro-resonator.
Further, the automatic gain control circuit AGC comprises a full-wave rectifying circuit, a low-pass filter circuit, a PI control circuit and a multiplier which are connected in sequence;
the full-wave rectification circuit is connected with the C/V interface detection circuit and is used for detecting a signal VsConverting the middle-negative half-cycle signal into a positive half-cycle signal;
the low-pass filter circuit is used for performing low-pass filtering on an output signal of the full-wave rectifying circuit to extract an amplitude value of a detection signal;
the PI control circuit is used for extracting the amplitude value from the low-pass filter circuit and the reference voltage VrefComparing the difference values to obtain a DC gain signal Vg；
The multiplier is connected with the first input end S1 of the electric control switch and is used for outputting a direct current gain signal V output by the PI control circuitgAnd a detection signal VsMultiplying to obtain a driving voltage signal VdAnd then output to the driving electrode of the micro resonator to drive the micro resonator to vibrate.
When detecting the signal VsIs less than the reference voltage VrefThe driving signal V output by the automatic gain control circuitdThe amplitude of the vibration of the resonator is increased, and the detection current signal I obtained by the detection electrode of the resonator is increasedsBecomes large, thereby increasing the detection signal VsThe amplitude of (d); when detecting the signal VsIs greater than the reference voltage VrefThe driving signal V output by the automatic gain control circuitdThe vibration amplitude of the resonator is reduced, and the detection current signal I obtained by the resonator detection electrode is reducedsBecomes small, thereby reducing the detection signal VsThe amplitude of (c). After a period of time has stabilized, the signal V is detectedsWill be equal to the reference voltage VrefWill vibrate at its own natural frequency while maintaining a fixed amplitude. Thus, the detection signal VsHas the same frequency as the natural frequency of the resonator, and detects the signal VsThe magnitude of (c) is directly reflective of the magnitude of the resonator amplitude. By measuring the detection signal V in the calculation of the natural frequency and the quality factor of the resonatorsIs characteristic of the natural frequency of the resonator, measuring the detection signal VsThe rate of decay of the amplitude characterizes the rate of decay of the resonator amplitude.
Furthermore, the electric control switch is a single-pole double-throw switch controlled by the FPGA. When the first input end S1 of the electric control switch is closed and the second input end S2 is opened, the output end of the automatic gain control circuit is connected with the driving electrode of the micro resonator to form a closed loop driving circuit, and a driving signal V is generateddDriving the microresonator to operate at a stable amplitude; when the first input end S1 of the electric control switch is opened and the second input end S2 is closed, the driving electrode of the micro-resonator is grounded, the resonator enters a free oscillation mode, and the amplitude is gradually attenuated.
Further, in the above-mentioned case,the first comparator and the second comparator are used for collecting a detection signal VsAnd the digital signals are converted into digital signals and are transmitted to the FPGA for processing. The positive end inputs of the first comparator and the second comparator are both detection signals VsThe negative end inputs of the first comparator and the second comparator are respectively an upper threshold voltage Vth1And a lower threshold voltage Vth2Respectively, the output is a square wave signal Vb1、Vb2. When the input voltage of the positive end of the comparator is greater than that of the negative end, the comparator outputs high level; when the input voltage of the positive end of the comparator is smaller than that of the negative end, the comparator outputs low level. Set upper threshold voltage Vth1Lower threshold voltage Vth2According to the detected voltage VsFor maximum amplitude, e.g. threshold voltage V on the signalth1Can be set to a detection voltage Vs80% of amplitude, lower threshold voltage V of signalth2Can be set to the detection voltage Vs20% of the amplitude.
When the electric control switch S1 is opened and the electric control switch S2 is closed, the signal V is detectedsIs constant and the amplitude begins to decay, at which point the signal V can be detectedsThe natural frequency and quality factor of the microresonator are extracted. At this stage, two comparators detect signal VsThe specific acquisition process is shown in fig. 2 and mainly comprises the following three stages:
(a) detection signal VsHas a peak value greater than the upper threshold voltage Vth1E.g. t in FIG. 20To t1Stage (2): in each detection signal period of the stage, two comparator positive end detection signals VsThe voltage of the comparator is smaller than the reference voltage of the negative terminal, then larger than the reference voltage of the negative terminal, and finally smaller than the reference voltage of the negative terminal, so that the comparator outputs a low level, a high level and a low level in each period in sequence, and the comparator is a square wave signal. With detection of signal VsThe peak value of the comparator becomes smaller and smaller, and the time that the voltage of the positive end of the comparator is larger than the voltage of the negative end of the comparator becomes shorter and shorter, so that the square wave signal Vb1、Vb2The time of the middle and high level is shorter and shorter, namely the duty ratio of the signal is smaller and smaller;
(b) detection signal VsIs greater than the lower threshold voltage Vth2And is smallAt an upper threshold voltage Vth1E.g. t in FIG. 21To t2Stage (2): in each detection signal period of the stage, the positive terminal input voltage of the first comparator is always smaller than the negative terminal voltage, so that a constant low level is output; the state of the second comparator is still the same as that of the stage (a), and a square wave signal with gradually reduced duty ratio is output;
(c) detection signal VsIs less than the lower threshold voltage Vth2E.g. t in FIG. 22The later stage is as follows: in each detection signal period of the stage, the positive terminal input voltage of the two comparators is always smaller than the negative terminal voltage, so that the two comparators output constant low levels.
Furthermore, the field programmable gate array FPGA comprises a switch control module, a first counter, a second counter, a third counter, a natural frequency reading module, a quality factor reading module and a serial port output module;
the switch control module controls the on-off of the electric control switch by outputting high and low levels, and controls the three counters to collect output signals of the two comparators and clock signals. The control signal is in the form of square wave, and when the switch control module outputs high level, i.e. T in FIG. 31At the moment, the switch output end D is connected with the first switch input end S1, and the driving signal V output by the amplitude control circuitdThe three counters are closed and do not count at the moment; when the switch control module outputs a high level, i.e. T in FIG. 32At the moment, the switch output end D is connected with the second switch input end S2, the driving electrode of the resonator is grounded, the driving circuit is in an open loop, the resonator enters a free oscillation state, the amplitude of the resonator begins to gradually attenuate due to the existence of damping, and at the stage, the switch control module controls the three counters to collect output signals of the two comparators and clock signals; after the acquisition is finished, the switch control module outputs high level again to enable the resonator to enter a forced vibration state again, and therefore the operation is repeated.
The switch control module controls the on-off of the electric control switch by outputting high and low levels, and simultaneously controls the three counters to collect output signals of the two comparators and clock signals;
the input end of the first timer is connected with the output end of the first comparator, and the square wave signal V output by the first comparator is capturedb1The number of square waves output by the first comparator is counted;
the input end of the second timer is connected with the output end of the second comparator, and square wave signals V of the second comparator are capturedb2The number of the square waves output by the second comparator is counted;
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;
when the electric control switch S1 is turned off and the electric control switch S2 is turned on, the three timers start counting at the same time when the detection signal starts to attenuate, when the first comparator outputs a constant low level, the first counter stops counting, and the counting value is recorded as N1(ii) a When the second comparator outputs a constant low level, the second counter and the third counter stop counting, and the count values are respectively recorded as N2、Nr；
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;
the specific process is as follows: natural frequency of micro resonator and detection signal VsBy calculating the detection signal VsThe natural frequency of the microresonator is obtained. As described above, the second counter and the third counter start counting at the same time and end counting at the same time. The second counter collects square wave signal Vb1And the number of the detection signals VsThe same frequency; the third counter collects the number of clock signals and the clock frequency frKnown, therefore, the natural frequency f0Can be derived by the following formula:
the quality factor reading module calculates the quality factor of the resonator according to the counting values output by the first counter and the second counter;
the specific process is as follows: by definition, the quality factor Q of a resonator is typically calculated using the following equation:
in the formula, ωnRepresenting the natural frequency of the resonator and k the rate of decay of the resonator amplitude. From the above-mentioned acquisition stage, it can be seen that in the detection signal VsPeak voltage from upper threshold voltage Vth1Down to a lower threshold voltage Vth2During this time t, the FPGAs are collected together (N)2-N1) The square wave has the same frequency as the detection signal, so the period of time t can be calculated by the following formula:
thus, the resonator amplitude decay rate can be derived from the following equation:
then the formula (1) and (4) are substituted into the formula (2),
therefore, the natural frequency and the quality factor of the microresonator can be obtained by the equations (1) and (5). The calculation process of the formula (1) is realized in an FPGA natural frequency reading module, and the corresponding natural frequency can be obtained; and (3) realizing the calculation process of the formula (5) in the FPGA quality factor reading module to obtain the corresponding quality factor.
And the serial port output module is connected with the output ends of the natural frequency reading module and the quality factor reading module, and outputs the natural frequency and the quality factor calculated by the natural frequency reading module and the quality factor reading module in real time through a serial port.
Furthermore, the scheme can acquire and calculate a group of natural frequency and quality factor data in the on-off process of each group of switches, and the two parameters are acquired simultaneously in the same free vibration process, so that the real-time performance and the accuracy of the data are ensured.
Claims (4)
1. A synchronous measurement system for the natural frequency and the quality factor of a micro resonator is characterized by 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;
the input end of the C/V interface detection circuit is connected with the detection electrode of the micro-resonator, and the detection current signal I acquired by the detection electrode of the micro-resonatorsConverted into a detection signal Vs(ii) a The AGC circuit is connected with the output end of the C/V interface detection circuit and is used for controlling a detection signal VsAnd outputs a drive signal Vd(ii) a The first input end S1 of the electric control switch is connected with the output end of the automatic gain control circuit, the second input end S2 is grounded, and the output end is connected with the driving electrode of the resonator and is used for switching the vibration mode of the micro-resonator; the input ends of the two comparators are connected with the output end of the C/V interface detection circuit and used for collecting a detection signal Vs(ii) a The output ends of the two comparators are connected with a field programmable gate array FPGA; the on-off of the electric control switch is controlled by a field programmable gate array FPGA.
2. The measurement system according to claim 1, wherein the automatic gain control circuit AGC comprises a full-wave rectifying circuit, a low-pass filtering circuit, a PI control circuit, a multiplier, which are connected in sequence;
the full-wave rectification circuit is connected with the C/V interface detection circuit;
the low-pass filter circuit is used for performing low-pass filtering on an output signal of the full-wave rectifying circuit;
the PI control circuit is used for extracting the amplitude value from the low-pass filter circuit and the reference voltage VrefComparing the difference values to obtain a DC gain signal Vg；
The multiplier is connected with the first input end S1 of the electric control switch and is used for outputting a direct current gain signal V output by the PI control circuitgAnd a detection signal VsMultiplying to obtain a driving voltage signal VdAnd then output to the driving electrode of the micro resonator to drive the micro resonator to vibrate.
3. The measurement system of claim 1, wherein the Field Programmable Gate Array (FPGA) comprises a switch control module, a first counter, a second counter, a third counter;
the switch control module controls the on-off of the electric control switch by outputting high and low levels, and simultaneously controls the three counters to collect output signals of the two comparators and clock signals;
the input end of the first counter is connected with the output end of the first comparator;
the input end of the second counter is connected with the output end of the second comparator;
and the third counter inputs a standard clock signal and counts the number of square waves of the clock signal.
4. The measurement system of claim 1, wherein the electrically controlled switch is a single pole double throw switch.
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