CN118041353A - Phase-locked amplifier's frequency synchronization system and phase-locked amplifier - Google Patents
Phase-locked amplifier's frequency synchronization system and phase-locked amplifier Download PDFInfo
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Abstract
The embodiment of the invention discloses a frequency synchronization system of a phase-locked amplifier and the phase-locked amplifier. The frequency synchronization system of the lock-in amplifier comprises a phase adjustment module, a phase adjustment module and a phase adjustment module, wherein the phase adjustment module is used for outputting an initial reference signal and gradually reducing the frequency of the initial reference signal according to a preset step length; the oscillator is connected with the phase adjusting module and is used for generating a reference signal according to the initial reference signal and the input signal to be measured; the phase adjusting module is also used for adjusting the frequency of a target reference signal output by the oscillator according to the phase difference between the reference signal and the signal to be detected; the frequency of the target reference signal is converged with the frequency of the signal to be measured. 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 frequency 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. The 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 frequency 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.
In order to realize the technical problems, the invention adopts the following technical scheme:
The embodiment of the invention provides a frequency synchronization system of a phase-locked amplifier, which comprises the following components:
the phase adjusting module is used for outputting an initial reference signal and gradually reducing the frequency of the initial reference signal with a preset step length;
the oscillator is connected with the phase adjusting module and is used for generating a reference signal according to the initial reference signal and the input signal to be measured;
The phase adjusting module is further used for adjusting the frequency of the target reference signal output by the oscillator according to the phase difference between the reference signal and the signal to be detected; the frequency of the target reference signal is converged with the frequency of the signal to be detected.
Optionally, the phase adjustment 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 low-frequency signals in the mixed signals to pass through and filtering other signals;
the phase adjusting module is further configured to stop reducing the frequency of the initial reference signal when receiving the low-frequency signal output by the filtering unit.
Optionally, the filtering unit is configured to pass a frequency difference signal in the mixed signal, and filter other signals;
The phase adjustment module further comprises a phase calculation unit for calculating a phase difference value between the signal to be measured 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 less than or equal to 1/10 of the initial reference signal frequency.
Optionally, the phase adjustment 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.
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 of the filtering unit to the initial reference signal frequency, and omega r is the initial reference signal angular frequency;
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 frequency 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 frequency synchronization system of a lock-in amplifier as set forth in any of the first aspects.
The frequency synchronization system of the phase-locked amplifier provided by the embodiment of the invention is provided with the phase adjusting module, outputs an initial reference signal through the phase adjusting module, and gradually reduces the frequency of the initial reference signal with a preset step length. And generating a reference signal according to the initial reference signal and the input signal to be measured through an oscillator. The phase adjusting module adjusts the frequency of a target reference signal output to the oscillator according to the phase difference between the reference signal and the signal to be measured. Because the frequency of the target reference signal is the same as the frequency of the signal to be detected, the frequency of the reference signal output by the real-time adjusting oscillator is further improved to be consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier to the signal to be detected of the weak signal electronic equipment is further 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 frequency synchronization system of a lock-in amplifier according to an embodiment of the present invention;
Fig. 2 is a schematic diagram of a frequency synchronization system of another lock-in amplifier according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a frequency 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 frequency 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 frequency synchronization system of a lock-in amplifier according to an embodiment of the present invention. Referring to fig. 1, a frequency synchronization system 10 of a lock-in amplifier according to an embodiment of the present invention includes: the phase adjusting module 2 is used for outputting an initial reference signal, and gradually reducing the frequency of the initial reference signal with a preset step length; the oscillator 3 is connected with the phase adjusting module 2, and the oscillator 3 is used for generating a reference signal according to the initial reference signal and the input signal to be measured; the phase adjusting module 2 is further configured to adjust a frequency of a target reference signal output by the oscillator 3 according to a phase difference between the reference signal and the signal to be measured; the frequency of the target reference signal is converged with the frequency of the signal to be detected.
Specifically, an externally input signal to be measured may be input through the input interface 1. The phase adjusting module 2 is connected with the calculating module 4 and the oscillator 3, and the phase adjusting module 2 can output an initial reference signal with larger frequency to the oscillator 3 after being electrified. The frequency of the initial reference signal is higher than the frequency of the signal to be measured.
The oscillator 3 may generate a reference signal based on frequency information of the initial reference signal. The frequency of the reference signal generated by the oscillator 3 may deviate from the frequency information of the signal to be measured. The phase adjustment module 2 gradually reduces the frequency of the initial reference signal output by itself according to the difference between the phase of the reference signal and the phase of the signal to be measured. Illustratively, the phase adjustment module 2 may reduce the frequency of the initial reference signal in a first step.
By gradually reducing the frequency of the initial reference signal, a frequency close to the signal to be measured can be found.
The phase adjustment module 2 further gradually reduces the frequency of the initial reference signal output by itself according to the difference between the phase of the reference signal and the phase of the signal to be measured. Illustratively, the phase adjustment module 2 may reduce the frequency of the initial reference signal in a second step. The second step size is smaller than the first step size. For example, it may be configured that when the difference between the angular frequency of the initial reference signal and the angular frequency of the signal to be measured approaches zero, the phase adjustment module 2 determines the phase and frequency of the output reference signal as the frequency of the target reference signal based on the difference between the phase of the reference signal and the phase of the signal to be measured. When the frequency of the reference signal coincides with the frequency of the signal to be measured, the phase adjustment module 2 will stop the phase adjustment. The oscillator 3 outputs the adjusted reference signal. The frequency of the adjusted reference signal is consistent with the frequency of the signal to be detected, so that the demodulation precision of the signal to be detected according to the adjusted reference signal and the signal to be detected is higher. By the arrangement, the frequency of the reference signal is consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier to 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 adjusting module 2 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 reference signal output by the oscillator 3 to be consistent with the frequency of the signal to be detected in real time, thereby further improving the demodulation precision of the phase-locked amplifier on the signal to be detected of the weak signal electronic device.
The frequency synchronization system 10 of the lock-in amplifier 20 provided in this embodiment gradually reduces the frequency of the initial reference signal by setting the phase adjustment module 2, outputting the initial reference signal by the phase adjustment module 2, and using a preset step size. And generates a reference signal from the initial reference signal and the input signal to be measured by the oscillator 3. The phase adjustment module 2 adjusts the frequency of the target reference signal output to the oscillator 3 according to the phase difference between the reference signal and the signal to be measured. Since the frequency of the target reference signal is the same as the frequency of the signal to be detected, the frequency of the reference signal output by the real-time adjusting oscillator 3 is further improved to be consistent with the frequency of the signal to be detected, and the demodulation precision of the phase-locked amplifier 20 to the signal to be detected of the weak signal electronic equipment is further improved.
Optionally, fig. 2 is a schematic structural diagram of another frequency synchronization system of a lock-in amplifier according to an embodiment of the present invention. On the basis of the above embodiment, referring to fig. 2, the phase adjustment module 2 may include: and 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. Optionally, with continued reference to fig. 2, the phase adjustment module 2 may further include: a filtering unit 42, configured to pass low-frequency signals in the mixed signal, and filter other signals; the phase adjustment module 2 is further configured to stop reducing the frequency of the initial reference signal when receiving the low frequency signal output by the filtering unit 42.
Specifically, the mixer 41 may multiply the signal to be measured with the initial reference signal to generate a mixed signal of a plurality of frequency components, the mixed signal including the frequency difference signal and the frequency sum signal, i.e., the mixed signal including the frequency of the phase difference signal. The low frequency signal may be set to a signal having a frequency below a preset frequency threshold. The present embodiment provides a specific preferred method of how to determine that a frequency close to the signal under test has been found.
Optionally, with continued reference to fig. 2 based on the foregoing embodiments, the filtering unit 42 is optionally configured to pass the frequency difference signal in the mixed signal, and filter out other signals; the phase adjustment module 2 further comprises a phase calculation unit 22, wherein the phase calculation unit 22 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 calculation unit 22 is connected to the filtering unit 42. The phase adjustment module 2 is used for adjusting the phase difference signal according to the frequency difference signalDetermining a phase difference/>, between the signal to be measured and the initial reference signalThe oscillator 3 is arranged to provide a phase difference according to the phase difference/>Adjusting the oscillation frequency 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.
Specifically, the phase calculating unit 22 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 22 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 22 is not limited herein. The present embodiment gives a particularly preferred method of obtaining the phase difference.
Optionally, with continued reference to fig. 2 based on the above embodiments, the filtering unit 42 includes a low-pass filtering unit, where a cut-off frequency of the filtering unit 42 is less than or equal to 1/10 of the initial reference signal frequency.
Optionally, a filtering unit 42 is connected between the mixer 41 and the phase calculating unit 22, and the filtering unit 42 is configured to filter clutter in the mixed signal, so that the frequency difference signal passes through; the cut-off frequency of the filtering unit 42 is not greater than 1/10 of the reference signal frequency.
Specifically, the filtering unit 42 may include a low-pass filtering unit. The filtering unit 42 is configured to filter out high frequency noise signals and other unwanted components in the mixed signal, and to preserve low frequency signals, such as frequency difference signals. The low-pass filter means 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 filter means 42 is not limited herein. The embodiment gives specific preferable conditions of the filtering implementation scheme for judging whether the frequencies of the initial reference signal and the signal to be detected are close.
Optionally, with continued reference to fig. 2, the phase adjustment module 2 includes: a PID regulator 21, where the PID regulator 21 is connected to the phase calculation unit 22 and the oscillator 3, and the PID regulator 21 is configured to generate a frequency adjustment value according to a variation 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.
Specifically, the PID regulator 21 may include a first frequency adjustment phase and a second frequency adjustment phase. In the first frequency adjustment stage, when the difference between the angular frequency of the initial reference signal and the angular frequency of the signal to be measured is greater than a preset threshold value, no frequency difference signal is output after passing through the filtering unit 42; when the difference between the angular frequency of the initial reference signal and the angular frequency of the signal to be measured is less than or equal to the preset threshold, a frequency difference signal is output after passing through the filtering unit 42. At this point, the PID regulator 21 enters a second frequency adjustment phase. In the second frequency adjustment stage, the difference between the angular frequency of the initial reference signal and the angular frequency of the signal to be measured is delta, the angular frequency omega 0 of the signal to be measured is larger than the angular frequency omega r of the reference signal, and the sampling period of the PID regulator 21The frequency difference signal/>, of the next two adjacent samplesThe method comprises the following steps of: /(I)AndIn the/>For the initial phase difference,/>The ratio of the cut-off frequency of the filtering unit 42 to the reference signal frequency is n; the output of the filtering unit 42 received by the PID regulator 21 is the frequency difference signal/>
Optionally, with continued reference to fig. 2, 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 a variation of the phase difference value obtained by sampling twice with different time, and the variation of the phase difference value is positively correlated with the frequency adjustment value.
Specifically, the PID regulator 21 is connected to the phase calculation unit 22 and the oscillator 3, and the PID regulator 21 is configured to generate a frequency adjustment value according to 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 oscillator 3 is used for adjusting the oscillation frequency according to the frequency adjustment value and outputting a reference signal; wherein the frequency of the reference signal is consistent with the frequency of the signal to be measured. 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.
Optionally, fig. 3 is a schematic structural diagram of a frequency 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.
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; and the second mixer 412, the second mixer 412 is connected with the second output end and the input interface 1, and 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 42 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 22 is configured to calculate a tangent or a cotangent function value corresponding to a phase difference value between the signal to be measured and the initial reference signal according to the first frequency difference signal and the second frequency difference signal; the PID regulator 21 is configured to generate the frequency adjustment value based on the amount of change in the tangent or the cotangent function value obtained by sampling twice at different times.
Specifically, 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. By using a tangent or a cotangent function, it can be found whether the two samples span the repetition period of the function, whereas the sine or cosine function is not; to obtain a tangent or a cotangent function, the two signals are obtained with 90 degrees phase difference.
Illustratively, the first mixed signal and the second mixed signal are calculated by the following formula:
Wherein V psd1 is a first mixing signal, V psd2 is a second mixing signal, V sig is a voltage amplitude of a signal to be measured, V r is a voltage amplitude of a reference signal, omega 0 is an angular frequency of the signal to be measured, omega r is an angular frequency of the reference signal, For the phase of the signal to be measured,/>Is the reference signal phase.
Alternatively, with continued reference to fig. 3 on the basis of the above embodiments, the phase calculation unit 22 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 22 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 calculation unit 22 calculates 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. In the phase calculation unit 22, 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 22 is not limited in this regard, and may be implemented by a CORDIC algorithm, or by comparing rising or falling edges of signals, for example.
Optionally, when the difference between the angular frequency ω 0 of the signal to be detected and the angular frequency ω r of the reference signal is greater than a preset threshold, the filtering unit 42 is configured to filter the ac component, and the first mixing signal and the second mixing signal are both filtered to be 0.
When the difference between the angular frequency ω 0 of the signal to be measured and the angular frequency ω r of the reference signal is equal to the preset threshold, the filtering unit 42 is configured to filter the ac component, and the first mixed signal and the second mixed signal are filtered to obtain a frequency difference signal
When the difference between the angular frequency ω 0 of the signal to be measured and the angular frequency ω r of the reference signal is smaller than a preset threshold value, the signal to be measured and the initial reference signal can pass through the filtering unit 42 to output the frequency difference signalThe method comprises the following steps:
the phase calculation unit 22 is configured to calculate a phase difference value between the signal to be measured and the initial reference signal using the following formula:
Alternatively, with continued reference to FIG. 3, based on the embodiments described above, the sampling period of the PID regulator 21 Wherein: n is the ratio of the cut-off frequency to the initial reference signal frequency, ω r is the initial reference signal angular frequency; the PID regulator 21 is configured to generate the frequency adjustment value based on the amount of change in the tangent or the cotangent function value obtained by sampling two adjacent times. If the sampling period is too large, two adjacent samples always span the repetition period of the function, and the correct phase difference variation cannot be obtained.
An alternative embodiment may be to adjust the frequency and phase directly with the PID regulator 21, i.e. the PID regulator 21 gives a maximum frequency and is continuously decreasing. Values of Q (t) and I (t) can only be obtained when the angular frequency ω 0 of the signal to be measured is relatively close to the angular frequency ω r of the reference signal, otherwise all are filtered by the low-pass filtering unit. At this point a reference signal has been obtained that is close in frequency to the input signal to be measured.
In order to further refine the frequency of the reference signal, it is assumed that the difference between the angular frequency ω 0 of the current signal to be measured and the angular frequency ω r of the reference signal is Δ, and that the angular frequency ω 0 of the signal to be measured and the angular frequency ω r of the reference signal are large, k is the sampling period k of the PID regulator 21, then the frequency difference signal of two adjacent samples of the module 4 is calculated subsequentlyThe method comprises the following steps of: /(I)And/>
In the above-mentioned method, the step of,For initial phase difference, i.e. >The ratio of the cut-off frequency of the low-pass filtering unit to the reference signal frequency is n, then k needs to satisfy: /(I)This is so set because if k is greater than/>The span of two adjacent samples is larger than half the period pi/2 of the tangent function, so that when two samples just span the period of the tangent function, the phase difference cannot be obtained in comparison, and whether the two samples span the period of the tangent function cannot be known.
Alternatively, with continued reference to fig. 3, the change of the tangent or the residual function value obtained by two adjacent samplings of the PID regulator 21 is greater than or equal to 2, and the tangent or the residual function value obtained by two adjacent samplings is positive-negative or negative-positive, then resampling is performed to calculate the phase difference.
Based on the above definition, it can be known that if the frequency difference signal is sampled twice2 Or more, and either positive or negative, it may be determined that the two samples span the period of the tangent function, requiring resampling to calculate the phase difference. So configured, it can be determined whether the two samples span the repetition period of the function.
Since the tangent function is a monotonically increasing function, the difference delta between the angular frequency ω 0 of the signal under test and the angular frequency ω r of the reference signal can be continuously adjusted by the PID regulator 21 until the difference delta between the angular frequency ω 0 of the signal under test and the angular frequency ω r of the reference signal approaches the preset range.
Excluding the case where two samples span the period of the tangent function, when the adjacent two samples effectively sample the frequency difference signalThe variation being within a predetermined range, e.g. approximately 0, according to the frequency difference signal/>Can obtain the phase difference/>Use/>The reference signal output by the oscillator 3 is adjusted to achieve the same frequency and same phase, i.e. synchronization, of the target reference signal and the input signal to be measured.
It should be noted that: omega r is the angular frequency of the oscillator 3 and the output signal of the PID regulator 21 is used to control the amount of change in frequency and phase of the output signal of the oscillator 3. The PID regulator 21 receives the frequency difference signal after changing the reference frequency of the oscillator 3The phase difference/>, of the previous sample can be obtained based on two adjacent effective samplesPhase difference from the last sampleThereby determining whether the reference frequency of the oscillator 3 should be increased or decreased and determining how much the reference frequency of the oscillator 3 should be increased or decreased.
When the PID regulator 21 receives the frequency difference signalAlways within a predetermined range, for example, approximately 0, it is indicated that the current reference signal is the same frequency and phase as the input signal. When the frequency difference signal/>If the reference signal exceeds the preset range, the reference signal is indicated to have a difference in frequency and/or phase with the input signal. At this time, the frequency difference signal/>, is based onFurther judgment is made.
When the frequency difference signal is sampled twiceAlways constant, i.e. when the variation is within an acceptable range, the reference signal and the input signal have only phase difference, pass/>, theThe phase difference/>, can be obtained
When the frequency difference signalWhen the value is always a variation value, the reference signal and the input signal have a frequency difference, the angular frequency omega 0 of the signal to be detected and the angular frequency omega r of the reference signal are approximately 0 through the adjusting process of the PID regulator 21, and the final stable phase difference/>
By setting the cut-off frequency of the filter unit 42 to be no more than 1/10 or 1/100 of the reference signal frequency, it is convenient to determine whether the difference between ω 0 and ω r is small in the first frequency adjustment stage.
Optionally, fig. 4 is a schematic structural diagram of a frequency 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 frequency 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 21 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 frequency synchronization system 10 of the lock-in amplifier 20 set forth in any of the above embodiments. The beneficial effects of the frequency 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 (11)
1. A frequency synchronization system of a lock-in amplifier, comprising:
the phase adjusting module is used for outputting an initial reference signal and gradually reducing the frequency of the initial reference signal with a preset step length;
the oscillator is connected with the phase adjusting module and is used for generating a reference signal according to the initial reference signal and the input signal to be measured;
The phase adjusting module is further used for adjusting the frequency of the target reference signal output by the oscillator according to the phase difference between the reference signal and the signal to be detected; the frequency of the target reference signal is converged with the frequency of the signal to be detected.
2. The frequency synchronization system of a lock-in amplifier of claim 1, wherein the phase adjustment 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 low-frequency signals in the mixed signals to pass through and filtering other signals;
the phase adjusting module is further configured to stop reducing the frequency of the initial reference signal when receiving the low-frequency signal output by the filtering unit.
3. The frequency synchronization system of a lock-in amplifier according to claim 2, wherein the filtering unit is configured to pass a frequency difference signal in the mixed signal and filter out other signals;
The phase adjustment module further comprises a phase calculation unit for calculating a phase difference value between the signal to be measured and the initial reference signal according to the frequency difference signal.
4. The frequency synchronization system of a lock-in amplifier according to claim 2, wherein the filtering unit comprises a low-pass filtering unit, and a cut-off frequency of the filtering unit is less than or equal to 1/10 of the initial reference signal frequency.
5. A frequency synchronization system of a lock-in amplifier according to claim 3, wherein the phase adjustment 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.
6. The system according to claim 5, 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.
7. The frequency synchronization system of a lock-in amplifier of claim 6, 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.
8. The system of claim 7, 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, and omega r is the initial reference signal angular frequency;
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.
9. The system according to claim 8, 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.
10. The phase locked amplifier frequency synchronization system of claim 5, wherein the phase locked amplifier phase synchronization circuit further comprises:
The demodulation module is connected with the oscillator and is used for demodulating the signal to be detected according to the reference signal output by the oscillator.
11. A lock-in amplifier, comprising: a frequency synchronisation system for a lock-in amplifier as claimed in any one of claims 1 to 10.
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