CN1885043A - Digital control circuit and method for small phase-lock amplifier - Google Patents

Abstract

The invention relates to a digit control circuit technique, especially providing a digit contriol circuit of small-scale lock-in amplifier and relative method, wherein said method comprises: inputting tested signal and reference signal into multiplier, to generate middle signal; the middle signal via low-pass filter will generate output signal. And the circuit comprises: a programmed oscillator (1), a phase sensitive detector (3), a programmed phase shifter (4), and a low-pass filter (5).

Description

The digital control circuit of small phase-lock amplifier and method

Technical field

The present invention relates to the digital control circuit and the method for digital-control circuit technical field, particularly a kind of small phase-lock amplifier.

Background technology

Lock-in amplifier recovers instrument as a kind of signal.Vital role in weak signal measurement has caused that people pay attention to more and more widely.Because it has the ability of good output stability and strong filtering noise, and buried weak signal in sound absorption can be extracted and amplified, thereby be widely used in signal averager, signal correction device, photon counter, daytime is surveyed in superconduction and all need recover and measure the occasion of buried weak signal in noise.

Lock-in amplifier adopts heterodyne system oscillation technology very ripe in radio circuit, and the mode of measured signal by frequency transformation is transformed into direct current.

In the heterodyne system oscillation technology, be called as local oscillations signal (Local Oscillation), that be used to do multiplying, in lock-in amplifier, be called as contrast signal, import from the outside.Lock-in amplifier can (from measured signal) detect the component identical with this contrast signal frequency.In the various component of signals that in measured signal, comprised, have only that component identical just can be converted into direct current, thereby can pass through low-pass filter (LPF) with the contrast signal frequency.The component of other frequencies is not equal to zero AC signal because be converted into frequency, so be low pass filtering device (LPF) filtering.

Summary of the invention

Fundamental purpose of the present invention be to provide a kind of cheapness the miniature numerical control lock-in amplifier, utilize common integrated circuit, realize the programme-controlled of phase-locked amplification system, miniaturization.

It is characterized in that:

(1) signal detection process is realized computer control fully, and control signal adopts Transistor-Transistor Logic level, can be connected with any calculating meter systems easily.

(2) utilize common commercially available integrated circuit, small-sized, cheapness, reliable, performance is enough to satisfy the needs of domestic consumer.

A kind of method of digital control circuit of small phase-lock amplifier, signal to be measured and reference signal are input to multiplier, produce M signal after multiplying each other through multiplier, and M signal is through behind the low-pass filter, produce output signal, output signal is directly proportional with the amplitude of signal to be measured.

A kind of digital control circuit of small phase-lock amplifier, by program control oscillator (1), phase-sensitive detector (PSD) (3), program control phase shifter (4), low-pass filter (5) is formed, program control oscillator (1) input end is connected in program control phase shifter (4) input end, and the output terminal of program control phase shifter (4) is connected in phase-sensitive detector (PSD) (3), and the output terminal of phase-sensitive detector (PSD) (3) is connected in low-pass filter (5).

Between the input end of the input end of program control phase shifter (4) and phase-sensitive detector (PSD) (3), be connected with testing sample circuit (2).

Program control phase shifter (4) by resistance R t be connected in software switch (8) input end with by R _t, R _F, C _tThe RC phase shifter that operational amplifier (7) constitutes is formed, and software switch (8) is connected in the input end of operational amplifier (7).

Software switch (8) is AD7501.

Program control phase shifter (4) is composed in series by two-stage circuit.

Can adopt the universal demodulation chip to constitute program control small phase-lock amplifier.

Description of drawings

Fig. 1 is a theoretical principle synoptic diagram of the present invention.

Fig. 2 is an electrical block diagram of the present invention.

Fig. 3 is program control phase-shift circuit synoptic diagram.

Embodiment

As Fig. 1 signal, frequency transformation is undertaken by multiplying.

1 signal to be measured is: Asin (ω t+ α),

2 reference signals are sin (ω t+ β),

6 M signals after multiplying each other through 3 multipliers are: and Asin (ω t+ α) * sin (ω t+ β)=Acos (β-α)/2-Acos (2 ω t+ alpha+beta)/2.

Behind 4 low-pass filters, frequency is that the high fdrequency component Acos (2 ω t+ alpha+beta)/2 of 2 ω is filtered, and only remaining frequency is that 05 output signals are: Acos (β-α)/2, be directly proportional the purpose of the detection tiny signal that reaches with the amplitude of 1 signal to be measured.

General multiplying mimic channel, its linear degree and temperature stability all have problems.So, in the present invention, adopt on-off element to carry out synchronous detection, realize frequency transformation thus.By the synchro detection circuit that on-off element carried out, be called PSD (phase-sensitive detector (PSD), PhaseSensitive Detector), this is a cardiac component of forming lock-in amplifier.

It is that the square wave of ω is as contrast signal that the present invention adopts frequency, make the polarity upset of measured signal synchronously with contrast signal, just switch between the two * 1/ * (1), this is equivalent to signal to be measured and square wave multiplies each other, and square wave expands into fourier series and is:

$\frac{4}{\mathrm{\π}}\underset{n=0}{\overset{\∞}{\mathrm{\Σ}}}\frac{1}{2n+1}\sin \left[(2n+1)(\mathrm{\ωt}+\mathrm{\β})\right],$

With 1 signal to be measured is to be after Asin (ω t+ α) multiplies each other:

$\frac{2A}{\mathrm{\π}}\underset{2n+1}{\overset{\∞}{\mathrm{\Σ}}}\cos \left\{\mathrm{\ω}\right[1\±(2n+1)]t+[\mathrm{\α}\±(2n+1)\mathrm{\β}\left]\right\},$

Through the DC component behind 4 low-pass filters be: (2A)/π cos (alpha-beta), be directly proportional with the amplitude of 1 signal to be measured.The present invention adopts the AD630 detuner of Analog Devices company as PSD.

The output signal meeting of PSD is owing to the phase differential between measured signal and the contrast signal, and the very big variation of generation.Thus, the output signal of low-pass filter (LPF) (just lock-in amplifier is measured resulting value) also can change.

Except phase differential is 0 °, under other states, can not measure the size of measured signal well.Like this, just need be adjusted to the phase differential between contrast signal and the measured signal 0 °, and then be input to PSD.This phase-adjusted circuit is called phase-shift circuit (Phase Shifter), is requisite circuit in the lock-in amplifier.

According to principle, as shown in Figure 2, circuit of the present invention comprises:

1 program control oscillator is made of D/A chip and voltage controlled oscillator, produces contrast signal and the input signal that offers 2 testing samples.

2 testing samples, for having a constant impedance or being equivalent to the circuit under test of a constant impedance, its impedance is parameter to be measured.

3 phase-sensitive detector (PSD)s, become square wave with reference to signal transition, adopt on-off element to carry out synchronous detection, realize frequency transformation thus, in the various component of signals that in measured signal, comprised, have only that component identical with the contrast signal frequency just can be converted into direct current, the component of other frequencies is not equal to zero AC signal because be converted into frequency

4 program control phase shifters as shown in Figure 3, according to the break-make of each passage of instruction control software switch (8) of computing machine, change the R of the RC phase shifter that is made of operational amplifier (7) _tValue, thus input contrast signal (6) phase place changed, make output signal (9) consistent with the measured signal phase place.Phase-shift phase Ф (ω)=2tan-1 (ω/R _tC _t).

5 low-pass filters, the component of other frequencies of filtering are because of the AC signal that is converted into, and the direct current signal that allows to be transformed into by the component identical with the contrast signal frequency passes through.

Claims (9)

1. the method for the digital control circuit of a small phase-lock amplifier, it is characterized in that, signal to be measured and reference signal are input to multiplier, after multiplying each other, the process multiplier produces M signal, M signal is through behind the low-pass filter, produce output signal, output signal is directly proportional with the amplitude of signal to be measured.

2. according to the method for the digital control circuit of the lock-in amplifier of claim 1, it is characterized in that, signal to be measured is: Asin (ω t+ α), reference signal is sin (ω t+ β), M signal is: A[cos (β-α)/2-cos (2 ω t+ alpha+beta)/2], through behind the low-pass filter, output signal is: and Acos (β-α)/2.

3. the digital control circuit of a small phase-lock amplifier, by program control oscillator (1), phase-sensitive detector (PSD) (3), program control phase shifter (4), low-pass filter (5) is formed, and it is characterized in that program control oscillator (1) input end is connected in program control phase shifter (4) input end, the output terminal of program control phase shifter (4) is connected in phase-sensitive detector (PSD) (3), and the output terminal of phase-sensitive detector (PSD) (3) is connected in low-pass filter (5).

4. according to the digital control circuit of the small phase-lock amplifier of claim 3, it is characterized in that, between the input end of the input end of program control phase shifter (4) and phase-sensitive detector (PSD) (3), be connected with testing sample circuit (2).

5. according to the digital control circuit of the small phase-lock amplifier of claim 3, it is characterized in that program control phase shifter (4) is by resistance R _tBe connected in software switch (8) input end with by R _t, R _F, C _tThe RC phase shifter that operational amplifier (7) constitutes is formed, and software switch (8) is connected in the input end of operational amplifier (7).

6. according to the digital control circuit of the small phase-lock amplifier of claim 5, it is characterized in that software switch (8) is AD7501.

7. according to the digital control circuit of the small phase-lock amplifier of claim 5, it is characterized in that program control phase shifter (4) is composed in series by two-stage circuit.

8. according to the digital control circuit of the small phase-lock amplifier of claim 3, it is characterized in that, can adopt the universal demodulation chip to constitute program control small phase-lock amplifier.

9. according to the digital control circuit of the small phase-lock amplifier of claim 3, it is characterized in that phase-sensitive detector (PSD) (3) adopts AD630.

Images