CN104811146A - Anti-aberration frequency doubling interference locking amplification system based on reverse repeated m sequences - Google Patents

Abstract

The invention discloses an anti-aberration frequency doubling interference locking amplification system based on reverse repeated m sequences. The system comprises a reverse repeated m sequence signal generating unit, weak voltage signals to be measured, a chopper, a positive amplifier, a reverse amplifier, an analog switch, a low-pass filter, a direct current amplifier and an analog-to-digital converter, wherein the reverse repeated m sequence signal generating unit controls the work flow process of the whole locking amplification system, and the input information is collected, codes are used for generating the reverse repeated m sequences, the chopper is used for modulating the weak voltage signals into alternating signals, the positive amplifier, the reverse amplifier and the analog switch forms a digital correlator, the low-pass filter is used as an integrator of the whole locking amplification system; the direct current amplifier regulates the signals output by the low-pass filter into the collecting range of the analog-to-digital converter, and the analog-to-digital converter is used for collecting the output voltage of the direct current amplifier. The locking amplification system has the advantages that the signal-to-noise ratio can be improved, and the anti-jamming capability can be improved.

Description

A kind of Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence

Technical field

The present invention relates to lock-in amplifier field, particularly relate to a kind of Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence.

Background technology

Engineering needs detected amplitude little, change slowly or direct current signal time Target to enlarge means usually can be selected to process.By faint, change signal slowly and, through ovennodulation, become the signal of interchange, thus avoid the DC shift problem of 1/f noise and amplifier.Sometimes in order to simplified design, (angular frequency is ω directly to utilize chopper faint signal madulation to be become periodic signal of square wave ₀), use the square-wave signal of same homophase frequently as reference signal drive analog switch again, positive half period conduct positive amplifier, negative half-cycle turn on inverter amplifier (being similar to rectification circuit), then the fluctuating signal that PSD exports is carried out filtering, filtering HFS, has just only been left with the relevant low frequency part of measured signal amplitude.

The signal of direct current signal less for amplitude or slowly change can be modulated with the carrier wave (square wave or sine wave) that the average of a fixed frequency is zero by lock-in amplifier, after amplifying, use reference signal (being generally the square wave with the same homophase frequently of modulation signal or sine wave) to carry out relevant treatment by analog circuit again, its output variable is only proportional with measured signal, every in correlation procedure all will by filtering with the incoherent noise signal of modulation signal, the noise that can greatly improve amplifying circuit improves ratio.Because reference signal and modulation signal are with frequency homophase, just the same with " pinning ", are therefore called Target to enlarge, are also lock-in amplify.

Lock-in amplifier can adopt analog multiplier to realize, but analog multiplier uses cumbersome in actual lock amplifier, most switch modulation method that adopts carries out Target to enlarge, namely under the control of reference signal (50% duty ratio) square wave, carries out reversal through modulated measured signal.Existing lock-in amplifier antithesis overtones band AF panel fine, but limited to the interference rejection capability of strange frequency multiplication, because the accumulation mean value of signal in a square-wave cycle of strange frequency multiplication is not 0, cannot offset completely.

Such as suppose that modulation signal is r (t), small-signal to be detected is a (is all generally direct current or approximate DC, be used as constant process), signal so after modulation is ar (t), if noise signal is n (t), so input signal x (t)=ar (t)+n (t), the Output rusults of lock-in amplifier is the cross-correlation function of x (t) and r (t):

$\begin{array}{c}{R}_{\mathrm{xr}}=\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^{T}x\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}\\ =\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^T[\mathrm{ar}\left(t\right)+n\left(t\right)]r(t-\mathrm{\τ})\mathrm{dt}\\ =\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^T\mathrm{ar}\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}+\underset{T\→\∞}{\lim }\frac{1}{T}n\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}\\ =a{R}_{\mathrm{rr}}+R_{\mathrm{rn}}\end{array}$

AR in result _rrbe the result that we will try to achieve, the inside contains the composition of measured signal a, R _rrthen the auto-correlation function of reference signal, as long as the phase difference of reference signal and modulation signal is fixed as zero, then R _rrbe exactly individual definite value, therefore aR _rronly change with the change of measured signal a, achieve the object of lock-in amplifier.

And R _rnit is the cross-correlation function of noise signal and reference signal, the physical significance of cross-correlation is exactly the similarity degree of two signals, from frequency domain, if noise n (t) has overlapping part with the frequency content of r (t), this is just non-vanishing, just creates interference to result.We said, general r (t) to be duty ratio be 50% square wave, the frequency content of square wave has ω ₀, 3 ω ₀, 5 ω ₀... etc. odd harmonic, if will have a negative impact to correlated results containing these odd harmonics in noise n (t) thus.

Therefore existing lock-in amplifier once some interference signal frequency close to or equal modulation signal, will to lock-in amplifier result produce harmful effect.When the frequency of interference signal is close to 3 ω ₀, 5 ω ₀, 7 ω ₀... fashion improves ratio by adding extra filter circuit to the noise improving equipment.But, once as interference signal frequency closely ω ₀time, filter circuit is very indistinguishable, and due to the coupling of equipment room in a lot of situation, interference signal just equals ω ₀, now Target to enlarge system can only distinguish interference signal and measured signal by phase place.

Traditional lock-in amplifier all realizes with pure hardware electronic system, all can bring many inconvenience in these research and development at equipment, debugging and upgrading, and the reading that brings of traditional pointer dial plate and precision problem also should improve.

Therefore, need to design a kind of brand-new Target to enlarge system, to resist strange frequency multiplication to disturb, precision is high, convenient reading, Parameter adjustable.

Summary of the invention

The present invention is directed to above-mentioned the deficiencies in the prior art, devise a kind of Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence.This Target to enlarge system greatly can increase the antijamming capability of system, simplify the complexity of system.

For solving the technical problem existed in above-mentioned prior art, the concrete technical scheme of employing is:

A kind of Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence, comprise invert-repeated m-sequence signal generation unit, weak voltage signals to be measured, chopper, forward amplifier, sign-changing amplifier, analog switch, low pass filter, direct current amplifier and analog to digital converter, wherein:

Described invert-repeated m-sequence signal generation unit is for controlling the workflow of whole Target to enlarge system, Gather and input information, code is utilized to produce invert-repeated m-sequence, control the output voltage that analog to digital converter gathers each amplifier, and internal composition there is filtering algorithm to improve the signal to noise ratio of whole Target to enlarge system;

Described chopper is used for weak voltage signals to be measured to be modulated into alternating signal, and the signal amplitude after modulation is the amplitude of measured signal, and waveform is invert-repeated m-sequence;

Described forward amplifier, inverting amplifier and analog switch form digital correlator;

Described low pass filter is in order to the integrator as whole Target to enlarge system;

The Signal Regulation that low pass filter exports by described direct current amplifier is in the acquisition range of analog to digital converter;

Described analog to digital converter is for gathering the output voltage of direct current amplifier.

Preferred scheme, described invert-repeated m-sequence signal generation unit comprises shift register and feedback network, and described invert-repeated m-sequence signal adds feedback network by shift register and produces.

Preferred technical scheme further, described invert-repeated m-sequence signal generation unit comprises single-chip microcomputer, keyboard and LCD display; Described single-chip microcomputer is for controlling the workflow of whole Target to enlarge system, Gather and input information, code is utilized to produce invert-repeated m-sequence, control AD gathers amplifier output voltage, and internal composition has filtering algorithm to improve the signal to noise ratio of whole Target to enlarge system, described invert-repeated m-sequence signal is produced by single-chip microcomputer; Described keyboard is for inputting the invert-repeated m-sequence length needing to produce, and the transmission frequency of sequence; Described LCD display, for display reminding interface during man-machine interaction, shows testing result when detecting for Target to enlarge.

By adopting such scheme, compared with prior art, its technique effect is the Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence of the present invention:

1. the square wave being 50% by the reference signal of lock-in amplifier by duty ratio changes the excellent invert-repeated m-sequence of autocorrelation into, substantially increases the antijamming capability of system.

2. can saving the filter circuit of the originally design in order to suppress strange frequency multiplication to be disturbed after employing invert-repeated m-sequence, simplifying the complexity of system.

3. produce invert-repeated m-sequence with single-chip microcomputer, its length, the cycle is by program control, flexible and changeable, realizes simple.

4. single-chip microcomputer carries out digital filtering to the signal that AD samples, further filtering high fdrequency component, improves signal noise ratio improve ratio.

5. adopt LCD display display system parameter and collection result, convenient, intuitively.

Accompanying drawing explanation

Fig. 1 is that the shift register producing invert-repeated m-sequence signal adds feedback network;

Fig. 2 is the system flow chart that single-chip microcomputer produces invert-repeated m-sequence signal;

Fig. 3 is the auto-correlation function schematic diagram of the square wave in lock-in amplifier of the prior art;

Fig. 4 is the auto-correlation function schematic diagram of the invert-repeated m-sequence in Target to enlarge system of the present invention;

Fig. 5 is the suppression schematic diagram of square wave to 2 subharmonic;

Fig. 6 is the suppression schematic diagram of invert-repeated m-sequence to 2 subharmonic;

Fig. 7 is the suppression schematic diagram of square wave to 3 subharmonic;

Fig. 8 is the suppression schematic diagram of invert-repeated m-sequence to 3 subharmonic;

Fig. 9 is the structural representation of the Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence of embodiment 1.

Embodiment

For making the object, technical solutions and advantages of the present invention clearly understand, below in conjunction with instantiation, the present invention is described in more detail.Should be appreciated that, these describe just exemplary, and do not really want to limit the scope of the invention.In addition, in the following description, the description to known features and technology is eliminated, to avoid unnecessarily obscuring concept of the present invention.

As shown in Figure 1, the initial condition of linear feedback shift register is (a ₀a ₁a _n-2a _n-1), through the linear feedback that is once shifted, the input state of the shift register left end first order is

$a_n=c_1{a}_{n-1}+c_2{a}_{n-2}+\·\·\·+c_{n-1}{a}_1+c_n{a}_0=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{c}_i{a}_{n-i}$

Through k displacement, being then input as of the first order

$a_i=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{a}_i{a}_{l-i}$

Wherein, l=n+k-1 >=n, k=1,2,3 ...

According to recurrence Relation known, the input of the first order of shift register determined by the previous status of feedback logic and shift register.

Invert-repeated m-sequence could be formed every position negate by after the m sequence extension 2 times obtained.If gene comparision is long, then multiple chip is needed mutually to combine.The hardware of invert-repeated m-sequence is not produced at this and carry out too much description.

When described invert-repeated m-sequence signal is produced by Single Chip Microcomputer (SCM) program.It is identical that its generation principle follows the shift register of hardware to add feedback network, the only length N of shift register, initial condition a _n, feedback network c _nall controlled by Single Chip Microcomputer (SCM) program, its flow chart as shown in Figure 2:

The initial value a of register _n, feedback network c _nwith the form programming of constant array in the ROM of single-chip microcomputer, user selects suitable feedback network can be generated the m sequence of different length by process simulation shift register by keyboard.The m sequence length produced is N, leaves in RAM.Then be extended to the Repeated m-Sequences that length is 2N, then every position negate generate length be the invert-repeated m-sequence of 2N.

The time dependent waveform of invert-repeated m-sequence produced is r (t).R (t) is divided into two-way, one tunnel is used for driving chopper, small-signal a is modulated into alternating signal ar (t) according to r (t) wave form varies, ar (t) is amplified by in-phase amplifier and inverting amplifier simultaneously, produces signal Aar (t) and-Aar (t) (A is the multiplication factor of amplifier) of two-way phase place symmetry.Other road r (t) drive analog switch, makes two-way symmetric signal alternate conduction enter low pass filter.The process implementation of alternate conduction signal Aar (t) is multiplied with reference signal r's (t), low pass filter achieves the addition of multiplied result, and two processes achieve correlated process (relevant is exactly be added after two sequences are multiplied again) jointly.

Suppose that noise signal is n (t), so input signal x (t)=ar (t)+n (t), the Output rusults of lock-in amplifier is the cross-correlation function of x (t) and r (t):

$\begin{array}{c}{R}_{\mathrm{xr}}=\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^{T}x\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}\end{array}$

$\begin{array}{c}=\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^T[\mathrm{ar}\left(t\right)+n\left(t\right)]r(t-\mathrm{\τ})\mathrm{dt}\\ =\underset{T\→\∞}{\lim }\frac{1}{T}{\∫}_0^T\mathrm{ar}\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}+\underset{T\→\∞}{\lim }\frac{1}{T}n\left(t\right)r(t-\mathrm{\τ})\mathrm{dt}\\ =a{R}_{\mathrm{rr}}+R_{\mathrm{rn}}\end{array}$

AR in result _rrbe the result that we will try to achieve, the inside contains the composition of measured signal a, R _rrthen the auto-correlation function of reference signal, as long as the phase difference of reference signal and modulation signal is fixed as zero, then R _rrbe exactly individual definite value, therefore aR _rronly change with the change of measured signal a, achieve the object of lock-in amplifier.Because invert-repeated m-sequence r (t) is a kind of pseudo-random signal, there is no the ω as square-wave signal ₀, therefore can not there is the odd harmonic problem of traditional lock-in amplifier in angular frequency.The auto-correlation function simultaneously contrasting invert-repeated m-sequence and square wave can find, invert-repeated m-sequence has excellent autocorrelation, and when this makes multiple devices work simultaneously, interactional probability becomes very little.

Single-chip microcomputer is except producing required sequence easily, and the analog to digital converter of different accuracy of simultaneously can also arranging in pairs or groups meets different measurement demands.The analog signal that lock-in amplifier exports by single-chip microcomputer becomes digital signal to be stored in RAM by AD conversion to carry out digital filtering process, improve antijamming capability further.The result obtained is shown in lcd screen simultaneously, clear and intuitive, handled easily personnel reading and record.

If Fig. 3 is the auto-correlation function of square wave and the auto-correlation function of Fig. 4 invert-repeated m-sequence, the noise said above when interference signal is identical with reference signal and reference signal cross-correlation item R _rnjust become the auto-correlation function of reference signal, because measured signal and reference signal are synchronous (being produced by same source), no matter be square wave or invert-repeated m-sequence from autocorrelation function graph, they can reach maximum, give full play to the effect of lock-in amplifier.The phase difference of general noise and reference signal is random, want to allow noise reduce the impact of lock-in amplifier, the auto-correlation function of reference signal must have following characteristics: in the region that some is very narrow, amplitude is very high, give full play to the effect of lock-in amplifier, in other regions, amplitude is zero, make extraneous noise have larger probability to drop on this part, reduce the impact on Output rusults.Fig. 4 exactly just meets this characteristic, in one-period, only has only a few interference signal can drop in the larger region of amplitude, major part all dropped on amplitude close to zero region.And Fig. 3 is obviously weaker, only have a fraction of region can close to zero, most of region has by a relatively large margin.

As Fig. 5 to Fig. 8 four width figure respectively show at square wave and invert-repeated m-sequence antithesis frequency multiplication is disturbed and strange frequency multiplication is disturbed rejection ability.

For convenience of description, have chosen the invert-repeated m-sequence that length is 14, in order to contrast, square wave gets 7 cycles.

Square wave is to the suppression of 2 subharmonic as shown in Figure 5, Figure 6 shows that the suppression of invert-repeated m-sequence to 2 subharmonic, and after visible product, under long accumulation, harmonic wave produces to disturb and positive and negatively just to offset, and mean value is zero, and two kinds of modes all can well suppress.

Be the suppression of square wave to 3 subharmonic as shown in Figure 7, after product, forward half-wave has 28, and negative sense half-wave only has 14, and be also left 14 forward half-waves after having offset, mean value is non-vanishing, creates interference to Output rusults.

Be the suppression of invert-repeated m-sequence to 3 subharmonic as shown in Figure 8, after product, forward half-wave has 22, and negative sense half-wave has 20, is only left 2 forward half-waves, reduces 7 times than 14 under square-wave-shaped state after counteracting.This is also the rejection ability when sequence length is 14, if increase the length of invert-repeated m-sequence, its rejection ability can also significantly promote.

Embodiment 1: as shown in Figure 9: a kind of Target to enlarge system of the anti-strange frequency multiplication interference based on invert-repeated m-sequence, comprise MCU2 (single-chip microcomputer or be called micro-control unit), keyboard 1, LCD display 3, weak voltage signals to be measured 4, chopper 5, forward amplifier 6, sign-changing amplifier 7, analog switch 8, low pass filter 9, direct current amplifier 10 and analog to digital converter 11, wherein:

Described MCU2 is for controlling the workflow of whole Target to enlarge system, Gather and input information, code is utilized to produce invert-repeated m-sequence, control AD11 (analog to digital converter) gathers each amplifier output voltage, and internal composition has filtering algorithm to improve the signal to noise ratio of whole Target to enlarge system;

Described keyboard 1 is for inputting the invert-repeated m-sequence length needing to produce, and the transmission frequency of sequence;

Described LCD display 3, for display reminding interface during man-machine interaction, shows testing result when detecting for Target to enlarge;

Described chopper 5 is for being modulated into alternating signal by weak voltage signals to be measured, and the signal amplitude after modulation is the amplitude of measured signal, and waveform is invert-repeated m-sequence;

Described forward amplifier 6, inverting amplifier 7 and analog switch 8 form digital correlator;

Described low pass filter 9 is in order to the integrator as whole Target to enlarge system;

The Signal Regulation that low pass filter 9 exports by described direct current amplifier 10 is in the acquisition range of analog to digital converter 11;

Described analog to digital converter 11 is for gathering the output voltage of direct current amplifier 10.

Should be understood that, above-mentioned embodiment of the present invention only for exemplary illustration or explain principle of the present invention, and is not construed as limiting the invention.Therefore, any amendment made when not departing from thought of the present invention and scope, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.In addition, claims of the present invention be intended to contain fall into claims scope and border or this scope and border equivalents in whole change and amendment.

Claims (3)

1. the Target to enlarge system based on the anti-strange frequency multiplication interference of invert-repeated m-sequence, it is characterized in that: it comprises invert-repeated m-sequence signal generation unit, weak voltage signals to be measured, chopper, forward amplifier, sign-changing amplifier, analog switch, low pass filter, direct current amplifier and analog to digital converter, wherein:

Described invert-repeated m-sequence signal generation unit is for controlling the workflow of whole Target to enlarge system, Gather and input information, code is utilized to produce invert-repeated m-sequence, control the output voltage that analog to digital converter gathers each amplifier, and internal composition there is filtering algorithm to improve the signal to noise ratio of whole Target to enlarge system;

Described chopper is used for weak voltage signals to be measured to be modulated into alternating signal, and the signal amplitude after modulation is the amplitude of measured signal, and waveform is invert-repeated m-sequence;

Described forward amplifier, inverting amplifier and analog switch form digital correlator;

Described low pass filter is in order to the integrator as whole Target to enlarge system;

The Signal Regulation that low pass filter exports by described direct current amplifier is in the acquisition range of analog to digital converter;

Described analog to digital converter is for gathering the output voltage of direct current amplifier.

2. the Target to enlarge system of a kind of anti-strange frequency multiplication interference based on invert-repeated m-sequence according to claim 1, it is characterized in that: described invert-repeated m-sequence signal generation unit comprises shift register and feedback network, described invert-repeated m-sequence signal adds feedback network by shift register and produces.

3. the Target to enlarge system of a kind of anti-strange frequency multiplication interference based on invert-repeated m-sequence according to claim 1, is characterized in that: described invert-repeated m-sequence signal generation unit comprises single-chip microcomputer, keyboard and LCD display; Described single-chip microcomputer is for controlling the workflow of whole Target to enlarge system, Gather and input information, code is utilized to produce invert-repeated m-sequence, control AD gathers amplifier output voltage, and internal composition has filtering algorithm to improve the signal to noise ratio of whole Target to enlarge system, described invert-repeated m-sequence signal is produced by single-chip microcomputer; Described keyboard is for inputting the invert-repeated m-sequence length needing to produce, and the transmission frequency of sequence; Described LCD display, for display reminding interface during man-machine interaction, shows testing result when detecting for Target to enlarge.