CN109541991B - Automatic gain control system of resonant electromagnetic tuning fork chopper - Google Patents
Automatic gain control system of resonant electromagnetic tuning fork chopper Download PDFInfo
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- CN109541991B CN109541991B CN201811258741.4A CN201811258741A CN109541991B CN 109541991 B CN109541991 B CN 109541991B CN 201811258741 A CN201811258741 A CN 201811258741A CN 109541991 B CN109541991 B CN 109541991B
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Abstract
The invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which is characterized in that an FPGA (field programmable gate array) and DA (digital-to-analog) converter outputs a symmetrical square wave signal with controllable amplitude and natural resonant frequency of a tuning fork, the symmetrical square wave signal is amplified by unit gain power and then output to a driving end of the tuning fork chopper, and meanwhile, a feedback signal which can reflect the real-time amplitude of the tuning fork and is output by an induction end of the tuning fork chopper is received and is subjected to preamplification, band-pass filtering and peak value detection; the peak voltage is sampled by the AD converter and the FPGA, the FPGA dynamically adjusts code values output to the DA converter according to a difference value between the peak voltage and a target voltage, amplitude of a square wave signal is controlled, frequency of the square wave signal is controlled and generated by the FPGA, reliable starting vibration of various tuning forks can be guaranteed and the tuning forks can always work under inherent resonance frequency, the amplitude of the square wave signal is controlled by an automatic gain control method, the amplitude of the tuning forks is regularly detected and timely adjusted according to needs, and high amplitude stability of the tuning fork chopper can be guaranteed.
Description
Technical Field
The invention relates to the technical field of photoelectric detection, in particular to an automatic gain control system of a resonant electromagnetic tuning fork chopper.
Background
In a photoelectric detection system, a weak optical signal to be detected is often annihilated by a large amount of noise backgrounds such as stray light and electronic noise. In order to extract a signal to be detected from background noise, weak signal detection technologies such as synchronous detection and phase-sensitive detection are widely adopted. The modulation of the detected optical signal by the optical chopper to convert the direct current optical signal into an alternating signal with frequency characteristics is a necessary means for such weak signal detection technology. The resonant electromagnetic tuning fork chopper has the advantages of small volume, low power consumption, high stability and strong shock and vibration resistance.
In the use of the resonant electromagnetic tuning fork chopper, in order to ensure the stability of frequency and amplitude, a signal generator or an open-loop self-excited oscillation direct driving method is not generally adopted, but a closed-loop control system is constructed by an analog circuit, a driving signal is not provided from the outside, the tuning fork self-excited oscillation is relied on to start and maintain the oscillation, and then the amplitude is regulated and stabilized by the closed-loop control of the circuit. However, in practical application, because the parameters of the tuning fork are difficult to obtain accurately, the self-excitation condition calculated theoretically cannot cause the tuning fork to start oscillation, and circuit parameters need to be changed and tried repeatedly.
The tuning forks with different inherent resonance frequencies need to be independently calculated and debugged, even the tuning forks with the same inherent resonance frequency and different batches cannot work under the same set of circuit parameters due to the fact that the production process cannot guarantee that all parameters of the tuning forks are completely consistent. The driving circuit structure of the resonant electromagnetic tuning fork chopper is abnormal and complex, debugging is difficult, and research and development cost is high. Therefore, the invention provides a simple, convenient, efficient and highly applicable control method for the resonant electromagnetic tuning fork chopper while ensuring the stability of the tuning fork frequency and amplitude, which is a problem to be solved urgently by a person skilled in the art.
Disclosure of Invention
The embodiment of the invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which dynamically adjusts the amplitude of a natural resonant frequency signal output by a DA converter according to a target amplitude to realize automatic gain control of a tuning fork.
The invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which comprises a Field Programmable Gate Array (FPGA), a DA converter, a power amplification unit, an AD converter, a peak detection unit, a band-pass filtering unit and a pre-amplification unit, wherein the FPGA wants the DA converter to output a first code value and a second code value, the DA converter converts the first code value and the second code value into voltage values and outputs square wave signals of required types, unit gain class-AB complementary power amplification is carried out on the square wave signals to obtain tuning fork driving signals with the same inherent resonance frequency as the tuning fork chopper, the tuning fork driving signals are output to a driving end of the tuning fork chopper, the tuning fork chopper starts to vibrate under the driving of the tuning fork driving signals, an induction end of the tuning fork chopper generates induction signals, the pre-amplification unit pre-amplifies the induction signals and outputs the induction signals to the band-pass filtering unit, the band-pass filtering unit is used for performing band-pass filtering on the induction signal, adjusting the center frequency of the band-pass filtering unit to be the intrinsic resonance frequency of the tuning fork, obtaining a sine wave signal only containing the intrinsic resonance frequency components of the tuning fork and outputting the sine wave signal to the peak value detection unit, the peak value detection unit is used for detecting the voltage peak value of the sine wave signal, the FPGA is used for controlling the AD converter to perform voltage sampling on the peak value detection unit to obtain a voltage peak value, the voltage peak value is positively correlated with the amplitude of the tuning fork, the FPGA is used for comparing the voltage peak value obtained by sampling with a target amplitude value and adjusting the DA converter according to the comparison result so as to complete automatic gain control of the tuning fork chopper.
As an optional scheme, the FPGA is specifically configured to compare a sampled voltage peak value with a target amplitude value, and when the voltage peak value is smaller than the target amplitude value, adjust a code value output to the DA converter by the FPGA according to the difference value, increase the first code value and equivalently decrease the second code value, so that a peak-to-peak value of a square wave signal output by the DA converter is increased.
As an optional scheme, the FPGA is specifically configured to compare a sampled voltage peak value with a target amplitude value, and when the voltage peak value is greater than the target amplitude value, adjust a code value output to the DA converter by the FPGA according to the difference value, increase the second code value and equivalently decrease the first code value, so that a peak-to-peak value of the square wave signal output by the DA converter is decreased.
As an optional scheme, the FPGA is specifically configured to compare a sampled voltage peak value with a target amplitude value, and when the voltage peak value is the same as the target amplitude value, keep a code value output by the FPGA at present unchanged.
As an alternative scheme, the required types are that the waveform duty ratio is 50%, the frequency is the natural resonant frequency of the tuning fork, and the positive and negative peak values are the voltage values corresponding to the first code value and the second code value and have the same absolute value.
As an alternative scheme, the FPGA adopts Virtex-2 series 2V3000 of Xilinx company, the selected DA converter adopts a 12-bit DA converter AD667 of ADI company, and the input code value is 000HAnd FFFHRespectively corresponding to and outputting-10V voltage and +10V voltage.
As an alternative scheme, the updating period of each code value is 2ms, the frequency of the square wave signal is 500Hz, and the peak value is +/-10V.
As an optional scheme, the sampling period of the voltage peak value of the FPGA is smaller than the updating period of each set of code values.
According to the technical scheme, the embodiment of the invention has the following advantages:
the invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which is characterized in that an FPGA (field programmable gate array) and DA (digital-to-analog) converter outputs a symmetrical square wave signal with controllable amplitude and natural resonant frequency of a tuning fork, the symmetrical square wave signal is amplified by unit gain power and then output to a driving end of the tuning fork chopper, and meanwhile, a feedback signal which can reflect the real-time amplitude of the tuning fork and is output by an induction end of the tuning fork chopper is received and is subjected to preamplification, band-pass filtering and peak value detection; the peak voltage is sampled by the AD converter and the FPGA, the FPGA dynamically adjusts code values output to the DA converter according to a difference value between the peak voltage and a target voltage, amplitude of a square wave signal is controlled, frequency of the square wave signal is controlled and generated by the FPGA, reliable starting vibration of various tuning forks can be guaranteed and the tuning forks can always work under inherent resonance frequency, the amplitude of the square wave signal is controlled by an automatic gain control method, the amplitude of the tuning forks is regularly detected and timely adjusted according to needs, and high amplitude stability of the tuning fork chopper can be guaranteed.
Drawings
FIG. 1 is a block diagram of an automatic gain control system of a resonant electromagnetic tuning fork chopper according to the present invention;
FIG. 2 is a flow chart of the automatic gain control system of the resonant electromagnetic tuning fork chopper provided by the present invention;
FIG. 3 is a schematic diagram of a resonant electromagnetic tuning fork chopper in accordance with the present invention;
fig. 4 is a waveform diagram of a tuning fork driving signal output by a DA converter in the automatic gain control method of the resonant electromagnetic tuning fork chopper of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terms "first," "second," "third," "fourth," and the like in the description and in the claims, as well as in the drawings, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It will be appreciated that the data so used may be interchanged under appropriate circumstances such that the embodiments described herein may be practiced otherwise than as specifically illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Correspondingly, the invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which is shown in fig. 1 and 4 and comprises a field programmable gate array FPGA, a DA converter, a power amplification unit, an AD converter, a peak detection unit, a band-pass filtering unit and a pre-amplification unit, wherein the FPGA outputs a first code value and a second code value to the DA converter, the DA converter converts the first code value and the second code value into voltage values and outputs a square wave signal of a required type, unit gain class ab complementary power amplification is performed on the square wave signal to obtain a tuning fork driving signal with the same inherent resonance frequency as that of the tuning fork chopper, the tuning fork driving signal is output to a driving end of the tuning fork chopper, the chopper is driven by the tuning fork driving signal, and an induction end of the tuning fork chopper generates an induction signal, the pre-amplification unit pre-amplifies the induction signal and outputs the induction signal to the band-pass filtering unit, the band-pass filtering unit performs band-pass filtering on the induction signal, the center frequency of the band-pass filtering unit is adjusted to be tuning fork inherent resonance frequency, a sine wave signal only containing tuning fork inherent resonance frequency components is obtained and output to the peak detection unit, the peak detection unit is used for detecting the voltage peak value of the sine wave signal, the FPGA controls the AD converter to perform voltage sampling on the peak detection unit, a voltage peak value is obtained, the voltage peak value is in positive correlation with tuning fork amplitude, the FPGA compares the voltage peak value obtained by sampling with a target amplitude value, and the DA converter is adjusted according to a comparison result, so that automatic gain control of the tuning fork chopper is completed.
The FPGA is specifically used for comparing a voltage peak value obtained by sampling with a target amplitude value, when the voltage peak value is smaller than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to a difference value, the first code value is increased and the second code value is reduced in an equivalent manner, so that the peak-to-peak value of a square wave signal output by the DA converter is increased, when the voltage peak value is larger than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to the difference value, the second code value is increased and the first code value is reduced in an equivalent manner, so that the peak-to-peak value of the square wave signal output by the DA converter is reduced, and when the voltage peak value and the target amplitude value are the same.
The required types are that the waveform duty ratio is 50%, the frequency is the natural resonant frequency of the tuning fork, the positive and negative peak values are the voltage values corresponding to the first code value and the second code value, and the absolute values are the same.
In the infrared band detection, a CH10-90D-500Hz type electromagnetic tuning fork chopper of EOPC company in America is adopted to modulate an optical signal irradiated on an indium gallium arsenic detector. The selected FPGA is Virtex-2 series 2V3000 of Xilinx company; the selected DA converter is a 12-bit DA converter AD667 from ADI, Inc., with an input code value of 000HAnd FFFHRespectively corresponding to output voltages of-10V and + 10V. Therefore, the specific method of the automatic gain control system of the resonant electromagnetic tuning fork chopper provided by the invention is as follows:
s1, alternately outputting 000 by FPGAHAnd FFFHTo the DA converter, the update cycle of each set of code values is 2ms, and then S2 is executed;
s2, converting the code value output by the FPGA into a voltage value by the DA converter AD667, keeping the current output before updating the next code value group, enabling the output of the DA converter to be a square wave signal A1 with the duty ratio of 50%, the frequency of 500Hz and the peak value of +/-10V, and then executing S3;
s3, performing unit gain class AB complementary power amplification on the square wave signal A1 to enhance the driving capability of the square wave signal A1 to obtain a tuning fork driving signal A2, outputting the tuning fork driving signal A2 to the driving end of the tuning fork chopper, and then executing S4;
s4, the tuning fork chopper can start oscillation rapidly under the driving of the A2 signal, an induction signal A3 is generated at an induction end, and then S5 is executed;
s5, pre-amplifying and band-pass filtering the induction signal A3 by the pre-amplifying unit and the band-pass filtering unit, setting the center frequency of the band-pass filtering unit as the natural resonant frequency of the tuning fork to obtain a sine wave signal A4 only containing the natural resonant frequency component of the tuning fork, and then executing S6;
s6, detecting a voltage peak value V1 of the sine wave signal A4 by using a peak value detection unit, controlling an AD converter by using the FPGA to perform voltage sampling, wherein the sampling period is T, the size of the voltage peak value V1 is positively correlated with the amplitude of the tuning fork, the amplitude intensity of the tuning fork at the moment can be directly reflected, and then S7 is executed;
s7, the FPGA compares the sampled voltage peak value V1 with the target amplitude V2, if V1 is smaller than V2, the code value output to the DA converter is correspondingly adjusted according to the difference value, the code value A is increased, meanwhile, the code value B is reduced by the same amount, and the peak-to-peak value of the DA output square wave is increased; if V1 is greater than V2, the output code value is correspondingly adjusted according to the difference, the code value B is increased, meanwhile, the code value A is reduced by the same amount, and the peak-to-peak value of the DA output square wave is reduced. For example: will code value 000HAnd FFFHIs changed to 100HAnd EFFHReducing the peak value of the square wave output by the corresponding DA from +/-10V to +/-9.512V; until V1 is the same as V2, the current output code value is maintained. And circularly executing S1 to S7, continuously detecting the difference value between the tuning fork amplitude and the target amplitude and adjusting in time to realize the automatic gain control of the tuning fork chopper.
When the tuning fork has a reduced amplitude due to some external interference, the output signal A3 of the induction end is reduced, the filtered sine wave signal A4 is reduced, the detected voltage peak value V1 is reduced, and the difference value between the detected voltage peak value and the target amplitude value V2 is increased, so that the output code value of the FPGA is adjusted, the DA output square wave signal A1 and the driving signal A2 output to the driving end of the tuning fork chopper are increased, the amplitude of the tuning fork is increased, the tuning fork returns to the preset amplitude again, and the automatic gain control is completed.
In this embodiment, the sampling period of the FPGA for the voltage peak is smaller than the update period of each set of code values, so as to ensure timeliness of amplitude control.
The invention provides an automatic gain control system of a resonant electromagnetic tuning fork chopper, which is characterized in that an FPGA (field programmable gate array) and DA (digital-to-analog) converter outputs a symmetrical square wave signal with controllable amplitude and natural resonant frequency of a tuning fork, and the symmetrical square wave signal is amplified by unit gain power and then output to a driving end of the tuning fork chopper; meanwhile, receiving a feedback signal which is output by an induction end of the tuning fork chopper and can reflect the real-time amplitude of the tuning fork, and carrying out preamplification, band-pass filtering and peak detection on the signal; sampling the peak voltage by an AD converter and an FPGA; and the FPGA dynamically adjusts the code value output to the DA converter according to the difference value between the peak voltage and the target voltage, and controls the amplitude of the square wave signal. The frequency of the square wave signal is controlled and generated by the FPGA, so that the reliable oscillation starting of various tuning forks can be ensured and the tuning forks can always work under the inherent resonance frequency; the amplitude of the square wave signal is controlled by an automatic gain control method, the amplitude of the tuning fork is detected periodically and adjusted in time as required, and the high amplitude stability of the tuning fork chopper can be ensured.
Referring to fig. 2, 3 and 4, accordingly, the present invention provides a resonant electromagnetic tuning fork chopper automatic gain control method, which can be executed by the resonant electromagnetic tuning fork chopper automatic gain control system described above, and comprises:
s101, outputting a first code value and a second code value to a DA converter by the FPGA, determining the first code value and the second code value as a group of code values, wherein the updating period of each group of code values is the natural resonant frequency period of the target tuning fork, and the first code value is larger than the second code value.
The FPGA outputs a first code value and a second code value to the DA converter, the first code value and the second code value are defined as a group of code values, the updating period of each group of code values is the natural resonant frequency period of the target tuning fork, and the first code value is larger than the second code value.
And S102, converting the first code value and the second code value into voltage values by the DA converter, and outputting square wave signals of required types.
And the DA converter converts the first code value and the second code value into voltage values and outputs a square wave signal of a required type to the power amplification unit, wherein the duty ratio of the square wave signal is 50%, the frequency is the natural resonant frequency of the tuning fork, the positive and negative peak values are the voltage values corresponding to the first code value and the second code value, and the absolute values of the voltage values are the same, namely the first code value and the second code value are in positive and negative symmetry.
S103, performing unit gain class AB complementary power amplification on the square wave signal to obtain a tuning fork driving signal with the same inherent resonance frequency as the tuning fork chopper, and outputting the tuning fork driving signal to a driving end of the tuning fork chopper.
The power amplification unit adopts a unit gain class AB complementary power amplification circuit, performs unit gain class AB complementary power amplification on a square wave signal to obtain a tuning fork driving signal with the same inherent resonance frequency as the tuning fork chopper, outputs the tuning fork driving signal to the driving end of the tuning fork chopper, and the tuning fork chopper is provided with a driving end and an inducing end.
And S104, the tuning fork chopper starts to vibrate under the driving of the tuning fork driving signal, and an induction end of the tuning fork chopper generates an induction signal.
Because the tuning fork driving signal and the intrinsic resonance frequency of the tuning fork chopper are the same, the tuning fork chopper can start oscillation rapidly, the oscillation starting speed of the tuning fork is related to the initial values of the first code value A and the second code value B after the tuning fork starts to be powered on, the first code value A and the second code value B output by the FPGA are set to the maximum code value and the minimum code value of the DA converter, the initial driving signal obtained by the tuning fork can be strongest, the tuning fork starts oscillation rapidly, and an induction signal is generated at an induction end.
And S105, pre-amplifying and band-pass filtering the induction signal, and adjusting the center frequency of a band-pass filtering unit to be the natural tuning fork resonance frequency to obtain a sine wave signal only containing the natural tuning fork resonance frequency component.
The induction signal is used as a feedback signal and is output to the pre-amplification unit from the induction end, the pre-amplification unit is used for pre-amplifying the induction signal and then outputting the induction signal to the band-pass filtering unit, the band-pass filtering unit is used for carrying out band-pass filtering on the induction signal, the center frequency of the band-pass filtering unit is adjusted to be the tuning fork inherent resonance frequency, and a sine wave signal only containing tuning fork inherent resonance frequency components is obtained.
S106, detecting the voltage peak value of the sine wave signal by using a peak value detection unit, and controlling an AD converter by the FPGA to perform voltage sampling to obtain a voltage peak value, wherein the voltage peak value is positively correlated with the amplitude of the tuning fork.
The peak detection unit can be realized by adopting a peak detection circuit, the peak detection unit is an analog-to-digital converter, the AD converter is used for detecting the voltage peak value of the sinusoidal wave signal, the AD converter is used for sampling the voltage of the voltage peak value of the peak detection unit under the control of the FPGA, the sampling period is T, the size of the voltage peak value is positively correlated with the amplitude of the tuning fork, and the amplitude intensity of the tuning fork at the moment can be directly reflected.
And S107, the FPGA compares the sampled voltage peak value with a target amplitude value, and adjusts the DA converter according to the comparison result so as to complete the automatic gain control of the tuning fork chopper.
The FPGA compares a sampled voltage peak value with a target amplitude value, when the voltage peak value is smaller than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to a difference value, the first code value is increased, the second code value is reduced in an equivalent manner, the peak-peak value of a square wave signal output by the DA converter is increased, when the voltage peak value is larger than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to the difference value, the second code value is increased, the first code value is reduced in an equivalent manner, the peak-peak value of the square wave signal output by the DA converter is reduced, and when the voltage peak value and the target amplitude value are the same, the current code value output by the FPGA is kept unchanged.
The PGA dynamically adjusts the size of the output code value, and the first code value A and the second code value B are equal in change, and the updating period of each code value is kept unchanged, so that the DA output waveform is always a square wave with the frequency same as the natural resonant frequency of the tuning fork and with the positive and negative symmetry.
In this embodiment, the sampling period T of the voltage peak V1 by the FPGA should be smaller than the update period of each set of code values, so as to ensure timeliness of amplitude control.
If the difference between the voltage peak value V1 and the target amplitude value V2 is detected as B1, the FPGA is adjusted to output the first code value a and the second code value B correspondingly, and the peak-to-peak value variation value of the output square wave of the DA converter is B2, then B2 is K B1, where K may be a constant or a variable adjusted according to a certain predetermined rule, and the specific setting is to be considered comprehensively according to the desired adjustment speed, adjustment accuracy, FPGA resource condition, and the like. If K is a constant, the amplitude is controlled to be linear adjustment, if the adjustment speed is high and the occupied resources are small, the K is increased, and if the adjustment precision is high, the K is decreased, but the adjustment speed is correspondingly reduced. If K is a variable, there are a wide variety of control methods, such as: when the difference between V1 and V2 is greater than V3, setting K to K1; when the difference between V1 and V2 is greater than V4, setting K to K2; by analogy, the K value is increased when the difference value is large, so that the adjusting speed is high, the K value is reduced when the difference value is small, so that the adjusting precision is high, the amplitude is subjected to nonlinear control by reasonably setting a plurality of intervals, even some advanced control algorithms such as PID (proportion integration differentiation) and the like can be added, and the high-speed and high-precision amplitude control of the tuning fork chopper can be realized by using a small amount of resources. Therefore, the K value is selected in various ways and can be combined with various algorithms, and designers can perform secondary development on the basis.
The invention provides an automatic gain control method of a resonant electromagnetic tuning fork chopper, which comprises the steps of outputting a symmetrical square wave signal with controllable amplitude and frequency of the inherent resonant frequency of a tuning fork by an FPGA (field programmable gate array) and a DA (digital-to-analog) converter, amplifying the signal by unit gain power, outputting the amplified signal to a driving end of the tuning fork chopper, receiving a feedback signal which is output by an induction end of the tuning fork chopper and can reflect the real-time amplitude of the tuning fork, and carrying out pre-amplification, band-pass filtering and peak detection on the feedback signal; the peak voltage is sampled by the AD converter and the FPGA, the FPGA dynamically adjusts code values output to the DA converter according to a difference value between the peak voltage and a target voltage, amplitude of a square wave signal is controlled, frequency of the square wave signal is controlled and generated by the FPGA, reliable starting vibration of various tuning forks can be guaranteed and the tuning forks can always work under inherent resonance frequency, the amplitude of the square wave signal is controlled by an automatic gain control method, the amplitude of the tuning forks is regularly detected and timely adjusted according to needs, and high amplitude stability of the tuning fork chopper can be guaranteed.
The embodiment of the invention also provides an automatic gain control method of the resonant electromagnetic tuning fork chopper, which comprises the following steps:
step 201, alternately outputting a first code value A and a second code value B of a DA converter by an FPGA, wherein the first code value A is larger than the second code value B and is defined as a group of code values, the updating period of each group of code values is the period of the natural resonant frequency of the target tuning fork, and then executing step 202;
step 202: the DA converter converts the code value output by the FPGA into a voltage value, so that the DA converter outputs a square wave signal A1 with the waveform of 50% of duty ratio, the frequency of the duty ratio being the intrinsic resonance frequency of the tuning fork, the positive and negative peak values being the voltage values corresponding to the code value A and the code value B and the absolute values being the same, and then step 203 is executed;
step 203, performing unit gain class AB complementary power amplification on the square wave signal A1 to obtain a tuning fork driving signal A2, outputting the tuning fork driving signal A2 to a driving end of the tuning fork chopper, and then executing step 204;
in step 204, the driving signal a2 is the same as the natural resonant frequency of the tuning fork chopper, so that the tuning fork chopper will start oscillating rapidly under the driving of the driving signal a2 and generate the sensing signal A3 at the inducing end, and then step 205 is executed;
step 205, pre-amplifying and band-pass filtering the induction signal A3, setting the center frequency of the band-pass filtering unit as the tuning fork inherent resonance frequency, obtaining a sine wave signal A4 only containing tuning fork inherent resonance frequency components, and then executing step 206;
step 206, detecting a voltage peak value V1 of the sine wave signal A4 by using a peak value detection unit, controlling an AD converter by using the FPGA to perform voltage sampling, wherein the sampling period is T, the size of the voltage peak value V1 is positively correlated with the amplitude of the tuning fork, the amplitude intensity of the tuning fork at the moment can be directly reflected, and then, step 207 is executed;
step 207, comparing the sampled voltage peak value V1 with the target amplitude value V2 by the FPGA, correspondingly adjusting the code value output to the DA converter according to the difference value if the voltage peak value V1 is smaller than the target amplitude value V2, increasing the first code value A, and simultaneously reducing the second code value B by the same amount, so that the peak-to-peak value of the DA output square wave is increased; if the voltage peak value V1 is greater than the second voltage V2, the output code value is correspondingly adjusted according to the difference value, the second code value B is increased, meanwhile, the first code value A is reduced by the same amount, and the peak-to-peak value of the DA output square wave is reduced; until the voltage peak value V1 is the same as the target amplitude value V2, the current output code value is kept unchanged. And (5) circularly executing the steps I to VII, continuously detecting the difference value between the tuning fork amplitude and the target amplitude and adjusting in time to realize the automatic gain control of the tuning fork chopper.
According to the automatic gain control method for the resonant electromagnetic tuning fork chopper, the inherent resonant frequency signal of the tuning fork chopper is generated by the FPGA, so that the tuning fork can be ensured to start vibrating reliably, the problem that circuit parameters need to be debugged repeatedly in a simulated closed loop to enable the circuit parameters to meet the self-excited oscillation condition of the tuning fork is solved, and the debugging process and the circuit complexity are greatly simplified. Aiming at different tuning forks, the code value updating period in FPGA software is only required to be modified, so that the output frequency signal of the FPGA software is the inherent resonance frequency signal of the tuning fork, and the effective driving of various tuning forks can be realized. For the situation that the intrinsic resonance frequencies of tuning forks in different batches are different from the nominal value due to production processes and the like, the output square wave frequency can be easily consistent with the intrinsic resonance frequency of the tuning forks by finely adjusting the update period of the FPGA code value. The problems that components and parts need to be replaced and hardware circuits need to be debugged again when tuning forks are replaced are avoided, and the applicability is high. Aiming at different tuning fork chopper target amplitudes, the FPGA can perform automatic gain control on the tuning fork amplitudes by only modifying the target code values in FPGA software, and automatically adjust the maximum width of a slit when the tuning fork is opened, so that the intensity of optical signals reaching a detector is effectively controlled to meet various detection requirements. The inherent resonance frequency of the resonance type electromagnetic tuning fork chopper is generally below 1kHz, the frequency is very low for FPGA, and the precise control and adjustment of the frequency are easy to realize; the amplitude stability of the output signal is determined by the performance of the DA converter, so that the accuracy and stability of the frequency and the amplitude of the tuning fork are controllable and predictable, and the long-time high-stability oscillation of the tuning fork chopper can be realized.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
Those skilled in the art will appreciate that all or part of the steps in the methods of the above embodiments may be implemented by associated hardware instructed by a program, which may be stored in a computer-readable storage medium, and the storage medium may include: a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic or optical disk, or the like.
While the resonant electromagnetic tuning fork chopper automatic gain control system provided by the present invention has been described in detail, those skilled in the art will appreciate that the embodiments and applications of the system can be varied according to the spirit of the present invention.
Claims (5)
1. An automatic gain control system of a resonant electromagnetic tuning fork chopper is characterized by comprising a Field Programmable Gate Array (FPGA), a DA converter, a power amplification unit, an AD converter, a peak detection unit, a band-pass filtering unit and a pre-amplification unit, wherein the FPGA outputs a first code value and a second code value to the DA converter, the DA converter converts the first code value and the second code value into voltage values and outputs square wave signals of a required type, unit gain class-AB complementary power amplification is carried out on the square wave signals to obtain tuning fork driving signals with the same inherent resonance frequency as the tuning fork chopper, the tuning fork driving signals are output to a driving end of the tuning fork chopper, the tuning fork chopper starts to vibrate under the driving of the tuning fork driving signals, and an induction end of the tuning fork chopper generates induction signals, the pre-amplification unit pre-amplifies the induction signal and outputs the induction signal to the band-pass filtering unit, the band-pass filtering unit performs band-pass filtering on the induction signal, the center frequency of the band-pass filtering unit is adjusted to be tuning fork inherent resonance frequency, a sine wave signal only containing tuning fork inherent resonance frequency components is obtained and is output to the peak detection unit, the peak detection unit is used for detecting the voltage peak value of the sine wave signal, the FPGA controls the AD converter to perform voltage sampling on the peak detection unit, a voltage peak value is obtained, the voltage peak value is positively correlated with tuning fork amplitude, the FPGA compares the voltage peak value obtained by sampling with a target amplitude value, and the DA converter is adjusted according to a comparison result to complete automatic gain control of the tuning fork chopper; wherein:
voltage values corresponding to the first code value and the second code value are positive and negative peak values, wherein the absolute values of the positive and negative peak values are the same;
the FPGA compares the voltage peak value obtained by sampling with the target amplitude value, and adjusts the DA converter according to the comparison result, which comprises the following steps:
when the voltage peak value is smaller than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to the difference value, the first code value is increased, and the second code value is decreased in an equivalent manner, so that the peak-to-peak value of the square wave signal output by the DA converter is increased;
when the voltage peak value is larger than the target amplitude value, the code value output to the DA converter by the FPGA is adjusted according to the difference value, the second code value is increased, and the first code value is reduced in an equivalent manner, so that the peak-to-peak value of the square wave signal output by the DA converter is reduced;
and when the voltage peak value and the target amplitude value are the same, keeping the code value output by the FPGA unchanged.
2. The resonant electromagnetic tuning fork chopper automatic gain control system of claim 1, wherein the desired type is a waveform duty cycle of 50% and a frequency of a tuning fork natural resonant frequency.
3. The resonant electromagnetic tuning fork chopper automatic gain control system of claim 1, wherein the FPGA is provided in Virtex-2 series 2V3000 by Xilinx, selected DA converters are provided in a 12-bit DA converter AD667 by ADI, with an input code value of 000HAnd FFFHRespectively corresponding to and outputting-10V voltage and +10V voltage.
4. The resonant electromagnetic tuning fork chopper automatic gain control system of claim 3, wherein each set of code values has an update period of 2ms of the tuning fork's natural resonant frequency, and the square wave signal has a frequency of 500Hz and a peak-to-peak value of ± 10V.
5. The resonant electromagnetic tuning fork chopper automatic gain control system of claim 3, wherein the sampling period of the FPGA for the voltage peak is less than the update period of each set of code values.
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| US4631466A (en) * | 1985-04-25 | 1986-12-23 | Westinghouse Electric Corp. | Phase locked stepper motor controlled light chopper |
| JP2556910B2 (en) * | 1989-11-30 | 1996-11-27 | 浜松ホトニクス株式会社 | Light intensity change detector |
| JP3235099B2 (en) * | 1994-11-07 | 2001-12-04 | 松下電器産業株式会社 | Piezoelectric actuator and pyroelectric infrared sensor using the same |
| KR20060004003A (en) * | 2004-07-06 | 2006-01-12 | 김성호 | Precision chopping device for diagnostic instrument for helicobacter pylori with photoacoustic spectroscopy |
| WO2008026183A1 (en) * | 2006-08-31 | 2008-03-06 | Koninklijke Philips Electronics N.V. | Cavity-enhanced photo acoustic trace gas detector with improved feedback loop |
| CN101034056A (en) * | 2007-04-02 | 2007-09-12 | 云南瑞升烟草技术（集团）有限公司 | Device of quick measuring moisture content of cigarette materials |
| CN101118181A (en) * | 2007-07-26 | 2008-02-06 | 西安劳特电子有限责任公司 | Diapason resonant vibration type episcotister |
| CN103107780B (en) * | 2012-12-26 | 2015-10-14 | 清华大学深圳研究生院 | A kind of chopper amplifier |
| CN103117662B (en) * | 2013-03-08 | 2015-01-21 | 滁州学院 | PWM (pulse width modulation) chopping NC (numerical control) AC (Alternating Current) power supply |
| CN104181402A (en) * | 2014-08-18 | 2014-12-03 | 国家电网公司 | Direct-current electric field detecting device used under condition of hybrid electric field |
| CN204256263U (en) * | 2014-10-16 | 2015-04-08 | 西安毅达信息系统有限公司 | A kind of intelligent precise tuning fork chopper |
| CN104709699B (en) * | 2014-11-10 | 2017-12-29 | 昆山鸿吉瑞精密机械有限公司 | Pressure-adjusting type vibrates disk controller |
| CN204359370U (en) * | 2014-12-23 | 2015-05-27 | 重庆川仪自动化股份有限公司 | Ultrasonic Wave Flowmeter receive MUT signal intensity AGC (automatic gain control) system |
| CN107271368A (en) * | 2017-05-23 | 2017-10-20 | 哈尔滨工业大学 | A kind of interior cavity-enhanced photo acoustic spectrum-type trace-gas sensors device |
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