CN117728833A - Signal synchronization system of phase-locked amplifier and phase-locked amplifier - Google Patents
Signal synchronization system of phase-locked amplifier and phase-locked amplifier Download PDFInfo
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Abstract
The embodiment of the invention discloses a signal synchronization system of a phase-locked amplifier and the phase-locked amplifier. The signal synchronization system of the lock-in amplifier comprises an input interface, a signal processing module and a signal processing module, wherein the input interface is used for inputting a signal to be detected; the frequency detection module is connected with the input interface and is used for detecting frequency information of the signal to be detected; the oscillator is connected with the frequency detection module and is used for outputting a reference signal, and the initial frequency of the reference signal is the frequency information; the phase synchronization module is connected with the input interface and the oscillator and is used for adjusting the frequency of a target reference signal output by the oscillator according to the phase difference between the initial reference signal and the signal to be detected so that the frequency of the target reference signal is converged with the frequency of the signal to be detected. The technical scheme provided by the embodiment improves the consistency of the frequency between the input signal and the reference signal during signal demodulation and improves the accuracy of signal demodulation.
Description
Technical Field
The embodiment of the invention relates to the technical field of electronics, in particular to a signal synchronization system of a phase-locked amplifier and the phase-locked amplifier.
Background
With the development of electronic technology, performance requirements of electronic devices are increasing. A Lock-in Amplifier (Lock-in Amplifier) is an electronic device for detecting weak signals. In many research fields and industrial applications, such as material analysis and science, quantum physics, nano physics, semiconductor devices, etc., there is an increasing demand for devices and methods for effectively measuring small electrical signals in noisy environments.
In the existing lock-in amplifier, the frequency deviation between the input signal and the reference signal during signal demodulation causes low signal demodulation precision.
Disclosure of Invention
The embodiment of the invention provides a signal synchronization system of a phase-locked amplifier and the phase-locked amplifier, which are used for solving the problem that the signal demodulation precision is not high because of the deviation between the frequency of an input signal and a reference signal during signal demodulation of the phase-locked amplifier.
In order to realize the technical problems, the invention adopts the following technical scheme:
the embodiment of the invention provides a signal synchronization system of a phase-locked amplifier, which comprises the following components:
the input interface is used for inputting signals to be tested;
the frequency detection module is connected with the input interface and is used for detecting frequency information of the signal to be detected;
the oscillator is connected with the frequency detection module and is used for outputting a reference signal, and the initial frequency of the reference signal is the frequency information;
the phase synchronization module is connected with the input interface and the oscillator, and is used for adjusting the frequency of a target reference signal output by the oscillator according to the phase difference between an initial reference signal and the signal to be detected, so that the frequency of the target reference signal is converged with the frequency of the signal to be detected.
Optionally, the phase synchronization module includes:
the mixer is connected with the input interface and the output end of the oscillator and is used for multiplying the signal to be detected with the initial reference signal to generate a mixed signal;
the filtering unit is used for enabling the frequency difference signal in the mixed signal to pass through and filtering other signals;
and the phase calculation unit is used for calculating a phase difference value between the signal to be detected and the initial reference signal according to the frequency difference signal.
Optionally, the filtering unit includes a low-pass filtering unit, and a cut-off frequency of the filtering unit is not greater than a frequency of the initial reference signal.
Optionally, the phase synchronization module further includes:
the PID regulator is connected with the phase calculation unit and the oscillator and is used for generating a frequency adjustment value according to the change condition of the phase difference value;
the oscillator is used for adjusting the oscillation frequency according to the frequency adjustment value and outputting a target reference signal; wherein the frequency of the target reference signal is consistent with the frequency of the signal to be detected.
Optionally, the PID regulator is connected to the phase calculation unit and the oscillator, and the PID regulator is configured to generate a frequency adjustment value according to the variation of the phase difference value obtained by sampling twice at different times, and the variation of the phase difference value is positively correlated with the frequency adjustment value.
Optionally, the oscillator includes:
the first output end is used for outputting a first reference signal;
the second output end is used for outputting a second reference signal; wherein the first reference signal and the second reference signal are 90 ° out of phase; the phase of the first reference signal is the same as the phase of the oscillator; the frequency of the first reference signal is equal to the frequency of the second reference signal;
the mixer includes:
the first mixer is connected with the first output end and the input interface, and is used for multiplying the signal to be detected and the first reference signal and outputting a first mixed signal;
the second mixer is connected with the second output end and the input interface, and is used for multiplying the signal to be detected and the second reference signal and outputting a second mixed signal;
the filtering unit is used for filtering the first mixed signal to generate a first frequency difference signal and filtering the second mixed signal to generate a second frequency difference signal;
the phase calculation unit is used for calculating a tangent or a complementary cut function value corresponding to a phase difference value between the signal to be detected and the initial reference signal according to the first frequency difference signal and the second frequency difference signal;
the PID regulator is used for generating the frequency adjustment value according to the variation of the tangent or the cotangent function value obtained by sampling twice at different times.
Optionally, the sampling period of the PID regulatorWherein: n is the ratio of the cut-off frequency to the initial reference signal frequency,/v>Angular frequency for the initial reference signal;
the PID regulator is used for generating the frequency adjustment value according to the change quantity of the tangent or the cotangent function value obtained by two adjacent sampling.
Optionally, the variation of the tangent or the cotangent function value obtained by two adjacent samplings of the PID regulator is greater than or equal to 2, and the tangent or cotangent function value obtained by two adjacent samplings is positive-negative or negative-positive, and then resampling is performed to calculate the phase difference.
Optionally, the signal synchronization system of the lock-in amplifier further comprises:
the demodulation module is connected with the oscillator and the input interface and is used for demodulating the signal to be detected according to the reference signal output by the oscillator.
According to another aspect of the present invention, there is provided a lock-in amplifier including: the signal synchronization system of a lock-in amplifier according to any of the first aspect.
The signal synchronization system of the lock-in amplifier provided by the embodiment of the invention detects the frequency of the signal to be detected by the frequency detection module, and outputs the reference signal by the oscillator, wherein the initial frequency of the reference signal is frequency information. And the phase synchronization module is arranged to adjust the frequency of the target reference signal output by the oscillator in real time according to the difference value between the phases of the initial reference signal and the signal to be detected, so that the frequency of the target reference signal is converged with the frequency of the signal to be detected, the adjusted reference signal output by the oscillator is consistent with the frequency of the signal to be detected, the frequency of the reference signal output by the oscillator is consistent with the frequency of the signal to be detected in real time, and the demodulation precision of the phase-locked amplifier to the signal to be detected of the electronic equipment with weak signals is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly explain the drawings needed in the description of the embodiments of the present invention, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the contents of the embodiments of the present invention and these drawings without inventive effort for those skilled in the art.
Fig. 1 is a schematic diagram of a signal synchronization system of a lock-in amplifier according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a signal synchronization system of another lock-in amplifier according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a signal synchronization system of a further lock-in amplifier according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a signal synchronization system of a further lock-in amplifier according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a lock-in amplifier according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
Based on the above technical problems, the present embodiment proposes the following solutions:
fig. 1 is a schematic diagram of a signal synchronization system of a lock-in amplifier according to an embodiment of the present invention. Referring to fig. 1, a signal synchronization system 10 of a lock-in amplifier according to an embodiment of the present invention includes: an input interface 1 for inputting a signal to be measured; the frequency detection module 2 is connected with the input interface 1, and the frequency detection module 2 is used for detecting frequency information of a signal to be detected; the oscillator 3 is connected with the frequency detection module 2, the oscillator 3 is used for outputting a reference signal, and the initial frequency of the reference signal is frequency information; the phase synchronization module 4, the phase synchronization module 4 is connected with the input interface 1 and the oscillator 3, and the phase synchronization module 4 is used for adjusting the frequency of the target reference signal output by the oscillator 3 according to the phase difference between the initial reference signal and the signal to be detected, so that the frequency of the target reference signal is converged with the frequency of the signal to be detected.
Specifically, each reference signal output by the oscillator is a target reference signal relative to the previous reference signal before the change; each reference signal output by the oscillator is an initial reference signal with respect to the next reference signal after the change. That is, the reference signals include an initial reference signal and a target reference signal. The trend is that the target reference signal is closer to the frequency of the signal to be measured than the initial reference signal.
The signal to be measured is input through the input interface 1. The signal to be measured is input to the frequency detection module 2 and the phase synchronization module 4. The frequency detection module 2 extracts frequency information of the module to be detected according to the received signal to be detected. The oscillator 3 may generate a reference signal based on the frequency information output from the frequency detection module 2. The frequency information as the initial reference signal is as consistent as possible with the frequency information of the signal to be measured. The frequency information of the reference signal generated by the oscillator 3 may deviate from the frequency information of the signal to be measured. By setting the phase synchronization module 4, the phase synchronization module 4 adjusts the frequency of the target reference signal output by the oscillator 3 according to the difference between the phase of the initial reference signal and the phase of the signal to be measured, thereby causing the frequency of the target reference signal to converge with the frequency of the signal to be measured.
Illustratively, when the difference between the phase of the initial reference signal and the phase of the signal under test is greater than a preset threshold parameter, the frequency of the reference signal output by the oscillator 3 is adjusted such that the difference between the frequency of the reference signal output by the oscillator 3 and the phase of the signal under test is less than the preset threshold parameter. When the difference between the phase of the reference signal and the phase of the signal to be measured is smaller than or equal to a preset threshold parameter, the frequency of the reference signal is judged to be consistent with the frequency of the signal to be measured.
When the frequency of the target reference signal coincides with the frequency of the signal to be measured, the phase synchronization module 4 will stop the phase adjustment. The oscillator 3 outputs the adjusted target reference signal. The frequency of the target reference signal after adjustment is consistent with the frequency of the signal to be measured, so that the demodulation precision of the signal to be measured according to the target reference signal after adjustment and the signal to be measured is higher. By the arrangement, the frequency of the target reference signal is consistent with that of the signal to be detected, and the demodulation precision of the phase-locked amplifier 20 on the signal to be detected of the weak signal electronic equipment is improved.
On the other hand, when the frequency of the reference signal is inconsistent with the frequency of the signal to be detected along with the extension of the running time of the device, the phase synchronization module 4 can detect the phase difference between the signal to be detected and the reference signal in real time and feed back the phase difference signal to the oscillator 3 in real time, so as to adjust the frequency of the target reference signal output by the oscillator 3 to be consistent with the frequency of the signal to be detected in real time, and further improve the demodulation precision of the phase-locked amplifier 20 on the signal to be detected of the weak signal electronic device.
The signal synchronization system 10 of the lock-in amplifier 20 provided in this embodiment detects the frequency of the signal to be detected by setting the frequency detection module 2, and outputs the reference signal by setting the oscillator 3, and the initial frequency of the reference signal is the frequency information. And the phase synchronization module 4 is arranged to adjust the frequency of the target reference signal output by the oscillator 3 according to the difference value between the initial reference signal and the phase of the signal to be detected, so that the frequency of the target reference signal is converged with the frequency of the signal to be detected, the adjusted target reference signal output by the oscillator 3 is consistent with the frequency of the signal to be detected, the real-time adjustment of the frequency of the target reference signal output by the oscillator 3 is further realized to be consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier 20 on the signal to be detected of the weak signal electronic equipment is further improved.
Optionally, with continued reference to fig. 1 on the basis of the foregoing embodiment, the input end of the frequency detection module 2 is input with a signal to be detected, the output end of the frequency detection module 2 is connected with the oscillator 3, and the function of the frequency detection module 2 is to detect the frequency information of the signal to be detected. The frequency information is the initial frequency of the internal reference signal of the output of the oscillator 3. The advantages of this arrangement are: if no frequency detection module 2 inputs an initial frequency to the oscillator 3, which is the same as or similar to the frequency of the signal to be measured, the adjustment time will be relatively slow only by the PID adjustment of the phase synchronization module 4, especially if the initial frequency set by the oscillator 3 and the signal to be measured input externally are far apart. For example, the initial frequency of the oscillator 3 is set to 1MHz regardless of the frequency information of the input signal, and if the frequency of the signal to be measured is 1Hz, only the phase synchronization module 4 of the reference signal is used for the adaptive adjustment at this time to adjust the frequency of the oscillator 3 to 1Hz, which takes a long time. Since the phase synchronization module 4 of the reference signal adopts PID adjustment, the PID adjustment is a gradual adjustment process, which is suitable for fine adjustment. The present embodiment is not limited to the specific structure of the frequency detection module 2, and the frequency detection module 2 may include a counter, a Digital Signal Processor (DSP), and the like.
Optionally, fig. 2 is a schematic diagram of a signal synchronization system 10 of another lock-in amplifier 20 according to an embodiment of the present invention. On the basis of the above embodiment, referring to fig. 2, the phase synchronization module 4 may include: the mixer 41 is connected with the input interface 1 and the output end of the oscillator 3, and the mixer 41 is used for multiplying the signal to be detected with the initial reference signal to generate a mixed signal; a filtering unit 44, where the filtering unit 44 is configured to pass the frequency difference signal in the mixed signal, and filter out other signals; and a phase calculating unit 42, wherein the phase calculating unit 42 is used for calculating a phase difference value between the signal to be measured and the initial reference signal according to the mixed signal.
Specifically, the mixer 41 may multiply the signal to be measured with the initial reference signal to generate a mixed signal with a plurality of frequency components, where the mixed signal includes a frequency difference signal, that is, the mixed signal includes the frequency of the phase difference signal. This embodiment gives an alternative method of phase difference calculation.
Optionally, with continued reference to fig. 2 based on the above embodiments, the filtering unit 44 includes a low-pass filtering unit, and a cut-off frequency of the filtering unit 44 is not greater than a frequency of the initial reference signal.
Specifically, the filtering unit 44 may include a low-pass filter. The filtering unit 44 is configured to filter out the high-frequency noise signal and other unwanted components in the mixed signal, and to preserve the frequency difference signal. The low-pass filter may be an RC low-pass filter, an LC low-pass filter, a lover low-pass filter, a butterworth low-pass filter, a blocking low-pass filter, a digital low-pass filter, or the like, and the specific configuration of the filtering unit 44 is not limited here. This embodiment gives an alternative to letting through the frequency difference signal in the mixed signal.
Optionally, with continued reference to fig. 2, the phase synchronization module 4 may further include: and a phase calculating unit 42, the phase calculating unit 42 is connected to the filtering unit 44, and the phase calculating unit 42 is configured to calculate a phase difference value between the signal to be measured and the initial reference signal according to the frequency difference signal.
Specifically, the phase calculating unit 42 is configured to calculate a phase difference between the filtered signal to be measured and the initial reference signal. The structure of the phase calculation unit 42 may include a phase detector, a shift register, a phase locked loop, a differential amplifier, or the like, and the specific structure of the phase calculation unit 42 is not limited herein.
Optionally, with continued reference to fig. 2, the phase synchronization module 4 may further include: a PID regulator 43, the PID regulator 43 is connected with the phase calculation unit 42 and the oscillator 3, the PID regulator 43 is used for generating a frequency adjustment value according to the change condition of the phase difference value; the oscillator 3 is used for adjusting the oscillation frequency according to the frequency adjustment value and outputting a target reference signal; wherein the frequency of the target reference signal is consistent with the frequency of the signal to be measured.
Specifically, only the information of the phase difference can be obtained according to the phase difference value, and whether the two frequencies to be compared are consistent or not can be obtained according to the change condition of the phase difference value. The PID regulator 43 receives a phase difference value between the signal under test output by the phase calculation unit 42 and the initial reference signal. The PID regulator 43 generates a frequency adjustment value according to the variation of the phase difference value, and feeds back the frequency adjustment value to the oscillator 3 for frequency adjustment. By the arrangement, the frequency of the reference signal generated by the oscillator 3 according to the frequency adjustment value is consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier 20 on the signal to be detected of the weak signal electronic equipment is further improved.
Alternatively, a PID regulator 43 is connected to the phase calculation unit 42 and the oscillator 3, and the PID regulator 43 is configured to generate a frequency adjustment value based on the amount of change in the phase difference value obtained by sampling twice at different times, and the amount of change in the phase difference value is positively correlated with the frequency adjustment value. The technical scheme provided by the embodiment provides a specific preferred method for obtaining the phase difference value change condition.
Specifically, it is so arranged that the PID regulator 43 generates the frequency adjustment value according to the variation of the phase difference value, the frequency adjustment value can be generated using the variation of the phase difference value obtained from two different time samples, and the variation of the phase difference value is positively correlated with the frequency adjustment value. Illustratively, the larger the amount of change in the phase difference value, the larger the frequency adjustment value; the smaller the amount of change in the phase difference value, the smaller the frequency adjustment value. By the arrangement, the speed of adjusting the target reference signal by the PID regulator 43 is higher, so that the frequency of the reference signal generated by the oscillator 3 according to the frequency adjustment value is consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier 20 on the signal to be detected of the weak signal electronic equipment is further improved.
Optionally, fig. 3 is a schematic structural diagram of a signal synchronization system of a further lock-in amplifier according to an embodiment of the present invention. On the basis of the above embodiments, referring to fig. 3, the oscillator 3 may include: the first output end is used for outputting a first reference signal; the second output end is used for outputting a second reference signal; wherein the phases of the first reference signal and the second reference signal differ by 90 °; the phase of the first reference signal is the same as the phase of the oscillator 3; the frequency of the first reference signal is equal to the frequency of the second reference signal.
Specifically, this arrangement allows the oscillator 3 to output two reference signals that are 90 ° out of phase, so as to improve the accuracy of the reference signals after mixing by the mixer 41.
Alternatively, with continued reference to fig. 3, based on the above embodiments, the mixer 41 may include: the first mixer 411, the first mixer 411 is connected with the first output end and the input interface 1, the first mixer 411 is used for multiplying the signal to be detected and the first reference signal and outputting a first mixed signal; the second mixer 412, the second mixer 412 is connected to the second output end and the input interface 1, the second mixer 412 is used for multiplying the signal to be detected and the second reference signal, and outputting a second mixed signal; the filtering unit 44 is configured to filter the first mixed signal to generate a first frequency difference signal and filter the second mixed signal to generate a second frequency difference signal; the phase calculation unit 42 is configured to calculate a tangent or a complementary value corresponding to a phase difference value between the signal to be measured and the initial reference signal based on the first frequency difference signal and the second frequency difference signal; the PID regulator 43 is configured to generate a frequency adjustment value based on the amount of change in the tangent or the cotangent function value obtained by sampling twice at different times.
Illustratively, the first mixed signal and the second mixed signal are calculated by the following formula:
(1)
(2)
in the method, in the process of the invention,for the first mixing signal +.>For the second mixing signal->For the voltage amplitude of the signal to be measured,for the voltage amplitude of the reference signal, < >>For the angular frequency of the signal to be measured, < > is->For the reference signal angular frequency, +.>For the phase of the signal to be measured, < > is->Is the reference signal phase.
The first mixer 411 multiplies the signal to be measured by the first reference signal and outputs a first mixed signal, and the second mixer 412 multiplies the signal to be measured by the second reference signal and outputs a second mixed signal. The phase of the first mixed signal is different from the phase of the second mixed signal. Because of the tangent or cotangent function, it can be found whether the two samples span the repetition period of the function, and to obtain the tangent or cotangent function, the two signals with 90 deg. phase difference can be obtained.
Alternatively, with continued reference to fig. 3, the phase calculation unit 42 may include: a first input terminal connected to the first mixer 411, the first input terminal being configured to receive a first mixed signal; a second input coupled to the second mixer 412, the second input configured to receive a second mixed signal; and a phase calculating unit 42 for calculating a phase difference value between the signal to be measured and the initial reference signal based on the first mixed signal and the second mixed signal.
Specifically, the phase calculating unit 42 calculates the phase difference between the signal to be measured and the initial reference signal based on the first mixed signal and the second mixed signal. In the phase calculation unit 42, the phase difference of the signal to be measured and the initial reference signal is calculated. The specific calculation method of the phase calculation unit 42 is not limited in this regard, and may be implemented by a CORDIC algorithm, or by comparing rising or falling edges of signals.
Optionally, the sampling period of the PID regulator 43Wherein: n is the ratio of the cut-off frequency to the initial reference signal frequency, < >>Angular frequency is the initial reference signal; the PID regulator is used for generating a frequency adjustment value according to the change quantity of the tangent or the cotangent function value obtained by two adjacent sampling.
Exemplary, when the signal under test has an angular frequencyAngular frequency +.>When the frequency difference signal is larger than a preset frequency threshold, the filtering unit filters alternating current components, and the first mixed signal and the second mixed signal are subjected to filtering processing to be 0. The sampling period is too large, and two adjacent samples always span the repetition period of the function, so that the correct phase difference change condition cannot be obtained.
When the angular frequency of the signal to be measuredAngular frequency +.>When the frequency difference signal is equal to a preset frequency threshold value, the filtering unit filters alternating current components, and the first mixing signal and the second mixing signal are filtered to be:
（3）
（4）
（5）。
when the angular frequency of the signal to be measuredAngular frequency +.>When the frequency difference signal between the two signals is smaller than the preset frequency threshold value, the signal to be detected and the initial reference signal can pass through the filtering unit and be +.>The method comprises the following steps:
（6）
the phase difference value between the signal to be measured and the initial reference signal is calculated by adopting the following formula:
（7）。
by arranging the frequency detection module, the frequency detection module directly gives an angular frequency of the signal to be detectedNear reference signal angular frequency->Without requiring the PID controller to try continuously from the minimum frequency to the maximum frequency until the angular frequency +_with the signal to be measured is found>Near reference signal angular frequency->. Then through the step of PID controller, sampling with k as period, < >>To->For feedback, let the signal angular frequency to be measured +.>Angular frequency +.>The difference between them is trended to 0 and the phase of the signal to be measured is obtained +.>Phase +.>A phase difference phi between them.
The frequency detection module has a detection threshold value of frequency difference, and can rapidly detect the angular frequency of the signal to be detected when the frequency difference between the reference signal and the signal to be detected is greater than the detection threshold valueAngular frequency +.>The approach value of the difference delta between the two signals is output to the oscillator for adjustment, so that the adjustment of the angular frequency of the signal to be measured by the PID controller can be reducedAngular frequency +.>Time of the difference delta between them.
The oscillator firstly adjusts the frequency of an initial output signal of the oscillator according to the frequency of an external input signal detected by the frequency detection module, then mixes the initial output signal with the external input signal, the mixed signal enters the low-pass filter for filtering, the filtered signal enters the phase calculation module for calculating the phase difference, the calculated result is input into the PID controller, the output of the PID controller is fed back to the oscillator, the oscillator adjusts the frequency and the phase of the self output signal according to the feedback signal and synchronizes with the signal to be detected, and finally outputs a reference signal to the demodulation module for subsequent signal demodulation.
In general, the frequency detection module detects the angular frequency of the signal to be detectedAngular frequency +.>The difference delta between them is adjusted faster. PID controller is treated and is surveyed signal angular frequency +.>Angular frequency +.>The adjustment of the difference delta between them is highly accurate. The signal synchronization system of the lock-in amplifier provided by the embodiment can synchronize the internal reference signal with the external signal to be detected, and ensures the accuracy, the speed and the high efficiency of demodulation.
Optionally, the change amount of the tangent or the cotangent function value obtained by two adjacent sampling of the PID regulator is greater than or equal to 2, and the tangent or the cotangent function value obtained by two adjacent sampling is positive-negative or negative-positive, and then resampling is performed to calculate the phase difference. This arrangement makes it possible to determine whether the two samples span the repetition period of the function.
Optionally, fig. 4 is a schematic structural diagram of a signal synchronization system of a further lock-in amplifier according to an embodiment of the present invention. Based on the above embodiments, referring to fig. 4, the signal synchronization system 10 of the lock-in amplifier 20 may further include: the demodulation module 5, the demodulation module 5 is connected with the oscillator 3 and the input interface 1, and the demodulation module 5 is used for demodulating the signal to be detected according to the reference signal output by the oscillator 3.
Specifically, the oscillator 3 adjusts the frequency and phase of the signal output by itself according to the signal fed back by the PID regulator 43 to synchronize with the signal to be measured. The oscillator 3 uses the adjusted signal as a reference signal, the adjusted reference signal is input to a subsequent demodulation module 5, and the demodulation module 5 is used for demodulating the signal to be detected.
Fig. 5 is a schematic diagram of a lock-in amplifier according to an embodiment of the present invention. Referring to fig. 5, the lock-in amplifier 20 provided in this embodiment includes the signal synchronization system 10 of the lock-in amplifier 20 set forth in any of the above embodiments. The beneficial effects of the signal synchronization system 10 having the lock-in amplifier 20 according to any of the embodiments described above are not described herein.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (10)
1. A signal synchronization system of a lock-in amplifier, comprising:
the input interface is used for inputting signals to be tested;
the frequency detection module is connected with the input interface and is used for detecting frequency information of the signal to be detected;
the oscillator is connected with the frequency detection module and is used for outputting a reference signal, and the initial frequency of the reference signal is the frequency information;
the phase synchronization module is connected with the input interface and the oscillator, and is used for adjusting the frequency of a target reference signal output by the oscillator according to the phase difference between an initial reference signal and the signal to be detected, so that the frequency of the target reference signal is converged with the frequency of the signal to be detected.
2. The signal synchronization system of a lock-in amplifier of claim 1, wherein the phase synchronization module comprises:
the mixer is connected with the input interface and the output end of the oscillator and is used for multiplying the signal to be detected with the initial reference signal to generate a mixed signal;
the filtering unit is used for enabling the frequency difference signal in the mixed signal to pass through and filtering other signals;
and the phase calculation unit is used for calculating a phase difference value between the signal to be detected and the initial reference signal according to the frequency difference signal.
3. The signal synchronization system of a lock-in amplifier according to claim 2, wherein the filtering unit comprises a low-pass filtering unit having a cut-off frequency not greater than a frequency of the initial reference signal.
4. The signal synchronization system of a lock-in amplifier of claim 2, wherein the phase synchronization module further comprises:
the PID regulator is connected with the phase calculation unit and the oscillator and is used for generating a frequency adjustment value according to the change condition of the phase difference value;
the oscillator is used for adjusting the oscillation frequency according to the frequency adjustment value and outputting a target reference signal; wherein the frequency of the target reference signal is consistent with the frequency of the signal to be detected.
5. The signal synchronization system of a lock-in amplifier according to claim 4, wherein the PID regulator is connected to the phase calculation unit and the oscillator, the PID regulator is configured to generate a frequency adjustment value based on a variation of the phase difference value obtained by sampling twice with different times, and the variation of the phase difference value is positively correlated with the frequency adjustment value.
6. The signal synchronization system of a lock-in amplifier of claim 5, wherein the oscillator comprises:
the first output end is used for outputting a first reference signal;
the second output end is used for outputting a second reference signal; wherein the first reference signal and the second reference signal are 90 ° out of phase; the phase of the first reference signal is the same as the phase of the oscillator; the frequency of the first reference signal is equal to the frequency of the second reference signal;
the mixer includes:
the first mixer is connected with the first output end and the input interface, and is used for multiplying the signal to be detected and the first reference signal and outputting a first mixed signal;
the second mixer is connected with the second output end and the input interface, and is used for multiplying the signal to be detected and the second reference signal and outputting a second mixed signal;
the filtering unit is used for filtering the first mixed signal to generate a first frequency difference signal and filtering the second mixed signal to generate a second frequency difference signal;
the phase calculation unit is used for calculating a tangent or a complementary cut function value corresponding to a phase difference value between the signal to be detected and the initial reference signal according to the first frequency difference signal and the second frequency difference signal;
the PID regulator is used for generating the frequency adjustment value according to the variation of the tangent or the cotangent function value obtained by sampling twice at different times.
7. The signal synchronization system of a lock-in amplifier of claim 6, wherein the sampling period of the PID regulatorWherein: n is the ratio of the cut-off frequency of the filtering unit to the initial reference signal frequency,angular frequency for the initial reference signal;
the PID regulator is used for generating the frequency adjustment value according to the change quantity of the tangent or the cotangent function value obtained by two adjacent sampling.
8. The signal synchronization system of a lock-in amplifier according to claim 7, wherein the change amount of the tangent or the cotangent function value obtained by sampling the PID regulator two times adjacent to each other is 2 or more, and the tangent or the cotangent function value obtained by sampling the PID regulator two times adjacent to each other is positive to negative or negative to positive, and resampling is performed to calculate the phase difference.
9. The signal synchronization system of a lock-in amplifier of claim 4, wherein the phase synchronization circuit of the lock-in amplifier further comprises:
the demodulation module is connected with the oscillator and the input interface and is used for demodulating the signal to be detected according to the reference signal output by the oscillator.
10. A lock-in amplifier, comprising: a signal synchronization system of a lock-in amplifier as claimed in any one of claims 1 to 9.
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