CN101958861B - Virtual image inhibiting method and circuit - Google Patents

Abstract

The invention discloses a virtual image inhibiting method. Based on N-1-order finite impact response filter, a frequency-irrelevant virtual image correction algorithm and a coordinate rotating digital computing method are adopted, and the computing capacity of a system on chip is combined to inhibit virtual images of input signals. The method is characterized by comprising the following steps of: selecting N frequency points fi in the frequency band of an input signal, and generating a sinusoidal waveform corresponding to each frequency point fi one by one by adopting the coordinate rotating digital computing method; mixing and filtering the series of sinusoidal waveforms obtained with the input signal one by one, traversing the N frequency points fi, obtaining a set of two mixed paths of amplitude difference and phase difference, and inputting into the system on chip, solving an equation set that the set is associated with the N-1-order finite impact response filter to obtain N coefficient sets, and correcting the output two paths of amplitude difference and phase difference to inhibit virtual images through a method for assigning the N-1-order finite impact response filter.

Description

A kind of virtual image inhibition method and circuit thereof

Technical field

The present invention relates to a kind of signal processing method, relate in particular to the method for virtual image inhibition filtering in a kind of complex signal processing mode and realize circuit, reach under the situation of not interrupting the normal signal processing quadrature network that the adaptively correcting coupling changes with minimum hardware spending.

Background technology

In the Modern Communication System, receiver is the core of most critical.From intermediate frequency output, receiver mainly comprises the different structure that is applicable to real signal processing mode and complex signal processing dual mode.Handle from real signal, its receiver structure receives the local frequency of signal: f as shown in Figure 1 _LO=f _RF+ f _IF, virtual image frequency: f _IMG=f _RF+ 2f _IFThis tradition real signal processor can't distinguishing signal and the virtual image (as shown in Figure 2), generally can only rely on frequency management or radio-frequency filter to help reduce virtual image composition.

So-called frequency management, namely IF-FRE is set by wireless frequency administrative department, and when RF had signal to be selected, RF+2IF frequency place signal strength signal intensity will be lower than particular value (as shown in Figure 3) simultaneously; And utilize the characteristic of radio-frequency filter, and adopting the band pass filter of tool trap function, it is logical that frequency range to be selected is included into band, and virtual image frequency range is included into band resistance (as shown in Figure 4).Yet even so, the inhibition of virtual image signal still reaches the target in people's expectation far away.

Along with the quick application of economic development and radio communication, frequency range becomes one of commodity of most worthy.The radio band of 1 megahertz can be sold several hundred million and even billions of prices, and therefore, radio band is more and more crowded.In face of billions of profits, national wireless frequency administrative department has abandoned " frequency management " way that employing " arranges the forbidden band for frequency range to be selected ".Therefore, the receiver architecture that adopts real signal to handle must adopt and contain " radio frequency band filter of trap function " way.It is low-cost integrated that yet this method is not easy to realize.Especially variable in frequency range to be selected, under the variable situation of IF-FRE, this way almost can't realize reducing the function of virtual image signal strength signal intensity.

Can't differentiate the problem of signal to be selected and the virtual image in order to solve real signal processing receiver architecture, scientist and Electronics Engineers have invented the quadrature mixing receiver architecture of handling based on complex signal (as shown in Figure 5).From shown in the figure as seen, it needs two mutually orthogonal local oscillators (90 ° of phase differences)

LO _q＝cos(2πf _LOt)，LO _i＝sin(2πf _LOt)

${\mathrm{MF}}_i=\cos \left(2\mathrm{\π}{f}_{\mathrm{LO}}t\right)\cos \left(2\mathrm{\π}{f}_{\mathrm{RF}}t\right)=\frac{1}{2}[\cos 2\mathrm{\π}(f_{\mathrm{LO}}-f_{\mathrm{RF}})t+\cos 2\mathrm{\π}(f_{\mathrm{LO}}+f_{\mathrm{RF}})t]$

${\mathrm{MF}}_q=\sin \left(2\mathrm{\π}{f}_{\mathrm{LO}}t\right)\cos \left(2\mathrm{\π}{f}_{\mathrm{RF}}t\right)=\frac{1}{2}[\sin 2\mathrm{\π}(f_{\mathrm{LO}}-f_{\mathrm{RF}})t+\sin 2\mathrm{\π}(f_{\mathrm{LO}}+f_{\mathrm{RF}})t]$

${\mathrm{IF}}_i=\frac{1}{2}\cos 2\mathrm{\π}(f_{\mathrm{LO}}-f_{\mathrm{RF}})t$

${\mathrm{IF}}_q=\frac{1}{2}\sin 2\mathrm{\π}(f_{\mathrm{LO}}-f_{\mathrm{RF}})t$

Intermediate-freuqncy signal is thus: ${\mathrm{IF}}_i+{\mathrm{jIF}}_q=\frac{1}{2}{e}^{j2\mathrm{\π}(f_{\mathrm{LO}}-f_{\mathrm{RF}})t},$ $S_{\mathrm{IF}}=\frac{1}{2}{e}^{j2\mathrm{\π}{f}_{\mathrm{IF}}t}$

And the intermediate-freuqncy signal that the virtual image produces is: ${\mathrm{IMG}}_{\mathrm{IF}}=\frac{1}{2}{e}^{-j2\mathrm{\π}{f}_{\mathrm{IF}}t}$

When intermediate frequency signal and the virtual image by behind the complex signal filter as shown in Figure 6, the virtual image frequency range of negative frequency will be by filtering (gain be 1/B), the signal of positive frequency then is exaggerated (gain is A).The characterisitic parameter A of this filter and B have determined the virtual image of this receiver to suppress ability, i.e. virtual image rejection ratio IRR=A/B.This is one of most important parameter in the design of complex signal receiver, and virtual image rejection ratio is more big, and is more strong to the antijamming capability of virtual image signal.Under the situation that does not increase overhead, virtual image rejection ratio is the bigger the better.

Virtual image rejects trap has dual mode in circuit is realized, a kind of employing analog mode, the Simulating Multiphase position complex signal filter that namely adopts resistance-capacitance network to realize; Another adopts the Digital Signal Processing mode, and the complex signal filter is realized by digital filter.

Adopt Simulating Multiphase position complex filter as shown in Figure 7, virtual image rejection ratio depends on this filter characteristic fully.And the virtual image rejection ratio of this Simulating Multiphase position filter depends on the matching properties of resistance capacitance.In integrated circuit was made, matching capacity generally was no more than 50dB, so virtual image inhibition ability can not surpass 60dB yet.In addition, simulation complex signal filter needs a lot of resistance capacitances, if IF-FRE is very low, will need very big resistance or electric capacity, increase chip area on the one hand, on the one hand also may increase system power dissipation in addition, be unfavorable for adopting different process simultaneously, and these all to be the designer be unwilling to see.

Adopt the Digital Signal Processing mode to realize that the complex signal filter function can solve the variety of issue that simulation complex signal filter exists, and the quadrature two-way separately carries out digital quantization, can maximum possible eliminate the coupling of quadrature two-way, and reduce about half because the noise that frequency mixer and intermediate-frequency circuit bring, thereby improve the signal to noise ratio of system on the basis of not improving the analog circuit complexity.Yet, adopt the complex signal receiver structure of Digital Signal Processing mode as shown in Figure 8, because local oscillation signal possibly can't improve perfect orthogonal local oscillation on the one hand, there are mismatch in two-way independence intermediate frequency filtering and amplification path on the other hand, the two paths of signals of therefore so-called " quadrature " is not complete quadrature, and the gain difference of two-way, phase difference neither 90 degree.Therefore, suppress to proofread and correct if do not do the virtual image, adopt the receiver of structure shown in Figure 8, the virtual image suppresses ability generally can not surpass 60dB (the coupling requirement of at this time simulating two-way is very high, therefore needs very big area) yet.Introduce the virtual image and suppress correcting algorithm, greatly the raising system virtual image rejection ratio, perhaps reduce the coupling requirement of analog circuit, reduce chip area, reduce cost.

The existing virtual image suppresses correcting algorithm or needs very big hardware spending, or can only solve the two-way mismatch problems (thinking that namely gain and phase place difference are the constants with frequency-independent) of frequency-independent.Adopt the virtual image of frequency-independent to suppress the two-way mismatch problems that correcting algorithm comes emending frequency to be correlated with, (for example GSM of 200kHz bandwidth) is no more than in the circuit of 30dB in coupling in narrow band communication, and actual virtual image rejection ratio performance limitations is between 60-70dB; And in broadband connections in (WCDMA of 2Mhz), actual virtual image rejection ratio is limited between the 50-60dB, and in the television reception of 6-8 million bandwidth, this correcting algorithm can only guarantee the virtual image rejection ratio of 45-50dB substantially.Therefore, the virtual image of frequency-independent suppresses correcting algorithm and can't satisfy broadband connections (＞70dB) requirement.

Summary of the invention

In view of the progress present situation of above-mentioned communication reception technique and the defective of existence, the objective of the invention is to propose a kind of virtual image inhibition method and circuit thereof, receiver is carried out the virtual image suppress to proofread and correct, to satisfy broadband connections (＞70dB) requirement.

Purpose of the present invention will be achieved by the following technical programs:

A kind of virtual image inhibition method, based on the N-1 rank limit for length's unit impulse response filter arranged, adopt virtual image correcting algorithm and the rotation of coordinate numerical calculation method of frequency-independent, and the operational capability of coupling system level chip realizes that the virtual image of input signal suppresses, and is characterized in that: N Frequency point f in the selected input signal frequency range _i, and adopt the rotation of coordinate numerical calculation method to produce corresponding each Frequency point f one by one _iSinusoidal waveform; Again with a series of sinusoidal waveforms of gained one by one with input signal mixing, filtering, obtain the two-way amplitude difference of phase mixing and set and the input system level chip of phase difference after traveling through N Frequency point fi, by finding the solution the equation group that has limit for length's unit impulse response filter coefficient to be associated on described set and N-1 rank, obtaining quantity is the individual coefficient sets of N, and by the method that limit for length's unit impulse response filter assignment is arranged to described N-1 rank, proofread and correct two-way amplitude difference and the phase difference of output, suppress the virtual image.

Further, aforesaid a kind of virtual image inhibition method, wherein the process of virtual image inhibition and the normal process of input signal do not interfere with each other, and wherein this input signal is medium and low frequency signal or the intermediate-freuqncy signal of numeral.

In the above-mentioned virtual image inhibition method, the N of this input signal Frequency point f _iSelect and satisfy relational expression:

{ f _i}={ f ₁+ (i-1) * (f ₂-f ₁)/N+ (f ₂-f ₁)/2N}, i=1,2,3 ... N adopts the rotation of coordinate numerical calculation method to produce frequency corresponding to described N Frequency point f _iSinusoidal waveform.

And this set with the equation group that has limit for length's unit impulse response filter coefficient to be associated on N-1 rank is:

Wherein limit for length's unit impulse response filter coefficient is arranged is { a in order _j, j=1,2,3 ... N; The input signal frequency range is f ₁～f ₂And the Digital Signal Processing frequency of system level chip is f _s, f _s＞2f ₂, find the solution the coefficient { a of gained _jBe used for the N-1 rank limit for length's unit impulse response filter arranged, proofread and correct two-way amplitude difference and the phase difference of output, suppress the virtual image.

Further, aforesaid a kind of virtual image inhibition method, corresponding to the different scope of input signal frequency range, this virtual image inhibition method adopts optional low-pass filtering and bandpass filtering mode to carry out.When carrying out for the mode that adopts low-pass filtering, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method only is selected N Frequency point f from the input signal frequency range _iAnd when carrying out for the mode that adopts bandpass filtering, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method is selected N Frequency point f from the input signal frequency range _iWith band pass filter centre frequency f _cSum.

Purpose of the present invention can also be achieved by following circuit framework technology:

A kind of virtual image suppresses circuit, by the described virtual image of claim 1 inhibition method input signal is carried out virtual image modulation, it is characterized in that: described circuit comprises the signal input part of processor, two-way and the signal output part of two-way, and what wherein be connected with complex coefficient on one road signal I/O path has limit for length's unit impulse response filter; First output of described processor is connected to sine-wave generator, and the signal input part of described sine-wave generator and two-way inserts frequency mixer in the lump, again via low pass or after being with logical filter, digital signal inserts described processor, and second output of described processor links to each other with the coefficient settings receiving terminal that limit for length's unit impulse response filter is arranged of complex coefficient.

Further, aforesaid a kind of virtual image suppresses circuit, and wherein this processor is at least system level chip, or the single-chip microcomputer of the equal data computation ability of tool.

The application implementation of the present invention's a kind of virtual image inhibition method and circuit thereof, this correcting algorithm can move on the backstage under the situation of not interrupting the normal signal processing continuously, the coefficient that limit for length's unit impulse response filter is arranged that continuous updating is reconfigurable, the quadrature two-way that the adaptively correcting coupling changes, the virtual image that has solved frequency dependence suppresses the long-term difficult problem of correction, and has greatly reduced hardware spending.

Following constipation closes the embodiment accompanying drawing, the specific embodiment of the present invention is described in further detail, so that technical solution of the present invention is easier to understand, grasp.

Description of drawings

Fig. 1 is the circuit framework schematic diagram of prior art real signal receiver;

Fig. 2 is that the prior art real signal is handled the intermediate-freuqncy signal schematic diagram that can't distinguish signal and the virtual image;

Fig. 3 is the intermediate-freuqncy signal schematic diagram through frequency management embodiment illustrated in fig. 1;

Fig. 4 is the signal schematic representation through the radio frequency bandpass filtering embodiment illustrated in fig. 1;

Fig. 5 is the circuit framework schematic diagram of prior art complex signal receiver;

Fig. 6 is that the virtual image that the prior art complex signal is handled suppresses schematic diagram;

Fig. 7 is the circuit framework schematic diagram of prior art Simulating Multiphase position complex signal filter;

Fig. 8 is the circuit framework schematic diagram of the complex signal filter of prior art Digital Signal Processing;

Fig. 9 is the electrical architecture schematic diagram that the virtual image of the present invention suppresses circuit.

Embodiment

As shown in Figure 9, first output of this processor connects the forcing function generator of changeable frequency, digital signal after two analog input signals are changed through analog to digital converter simultaneously and the forcing function generator of changeable frequency are linked on the frequency mixer simultaneously, and then by frequency mixer connection wave digital lowpass filter or band pass filter, then the output of wave digital lowpass filter or band pass filter connects processor again and carries out data and handle, and second output of processor connects complex coefficient filter.One end of input signal connects after analog-to-digital conversion and exports complex coefficient filter to, the output of this complex coefficient filter suppresses one of back signal output part as the virtual image, and the other end of input signal directly suppresses the other end of signal output as the virtual image after analog-to-digital conversion.

In conjunction with actual operating position of the present invention, allowing signal obtain the virtual image suppresses, at first in two different analog signals of two input inputs, two different analog signals obtain obstructed digital quantity signal by analog to digital converter, two different digital quantity signals are sent in the frequency mixer, processor receives simultaneously, transmission information is to the changeable frequency forcing function generator, allow the changeable frequency forcing function generator send sinusoidal signal, sinusoidal signal and two the same being sent in the frequency mixer of digital quantity signal, allow frequency mixer handle these digital signals and sinusoidal signal, frequency mixer is sent to wave digital lowpass filter or band pass filter to digital signal and sinusoidal signal, by low-pass filtering or bandpass filtering waveform is carried out shaping, stick signal is suitable for the live part of computing, the signal that keeps is sent to processor, and the program that the operation of processor at this moment prelists is handled filtering signal, again the consequential signal behind the processor is exported to complex coefficient filter by second output at last and carries out virtual image inhibition.

Wherein processor to the process that filtering signal carries out computing is: N Frequency point f in the selected input signal frequency range _i, and adopt the rotation of coordinate numerical calculation method to produce corresponding each Frequency point f one by one _iSinusoidal waveform; Again with a series of sinusoidal waveforms of gained one by one with input signal mixing, filtering, obtain the two-way amplitude difference of phase mixing and set and the input system level chip of phase difference after traveling through N Frequency point fi, by finding the solution the equation group that has limit for length's unit impulse response filter coefficient to be associated on described set and N-1 rank, obtaining quantity is the individual coefficient sets of N, and by the method that limit for length's unit impulse response filter assignment is arranged to described N-1 rank, proofread and correct two-way amplitude difference and the phase difference of output.

The N of this input signal Frequency point f wherein _iSelect and satisfy relational expression:

{ f _i}={ f ₁+ (i-1) * (f ₂-f ₁)/N+ (f ₂-f ₁)/2N}, i=1,2,3 ... N adopts the rotation of coordinate numerical calculation method to produce frequency corresponding to described N Frequency point f _iSinusoidal waveform.

And this set with the equation group that has limit for length's unit impulse response filter coefficient to be associated on N-1 rank is:

Wherein limit for length's unit impulse response filter coefficient is arranged is { a in order _j, j=1,2,3 ... N; The input signal frequency range is f ₁～f ₂And the Digital Signal Processing frequency of system level chip is f _s, f _s＞2f ₂, find the solution the coefficient { a of gained _jBe used for the N-1 rank limit for length's unit impulse response filter arranged.

Consider the scope that the input signal frequency range is different, this virtual image inhibition method adopts optional low-pass filtering and bandpass filtering mode to carry out.When carrying out for the mode that adopts low-pass filtering, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method only is selected N Frequency point f from the input signal frequency range _iAnd when carrying out for the mode that adopts bandpass filtering, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method is selected N Frequency point f from the input signal frequency range _iWith band pass filter centre frequency f _cSum.

By above-mentioned character express also by reference to the accompanying drawings as can be seen, behind employing the present invention, can finish the virtual image is suppressed through complex coefficient filter, digital lowpass or band pass filter, changeable frequency forcing function generator, frequency mixer by processor.

Certainly, more than only be concrete exemplary applications of the present invention, protection scope of the present invention is not constituted any limitation.In addition to the implementation, the present invention can also have other execution mode.All employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop within the present invention's scope required for protection.

Claims (8)

1. virtual image inhibition method, based on the N-1 rank limit for length's unit impulse response filter arranged, adopt virtual image correcting algorithm and the rotation of coordinate numerical calculation method of frequency-independent, and the operational capability of coupling system level chip realizes that the virtual image of input signal suppresses, and is characterized in that: N Frequency point f in the selected input signal frequency range _i, and adopt the rotation of coordinate numerical calculation method to produce corresponding each Frequency point f one by one _iSinusoidal waveform; Again with a series of sinusoidal waveforms of gained one by one with input signal mixing, filtering, travel through N Frequency point f _iAfter obtain the two-way amplitude difference of phase mixing and set and the input system level chip of phase difference, by finding the solution the equation group that has limit for length's unit impulse response filter coefficient to be associated on described set and N-1 rank, obtaining quantity is the individual coefficient sets of N, and by the method that limit for length's unit impulse response filter assignment is arranged to described N-1 rank, proofread and correct two-way amplitude difference and the phase difference of output, suppress the virtual image, wherein said set with the equation group that has limit for length's unit impulse response filter coefficient to be associated on N-1 rank is:

, it is { a that order has limit for length's unit impulse response filter coefficient _j, j=1,2,3 ... N; The input signal frequency range is f ₁～f ₂And the Digital Signal Processing frequency of system level chip is f _s, f _s2f ₂

2. a kind of virtual image inhibition method according to claim 1 is characterized in that: the process that the described virtual image suppresses does not interfere with each other with the normal process of described input signal, and wherein said input signal is digital medium and low frequency signal or intermediate-freuqncy signal.

3. a kind of virtual image inhibition method according to claim 1 is characterized in that: the N of described input signal Frequency point f _iSelect and satisfy relational expression:

{ f _i}={ f ₁+ (i-1) * (f ₂-f ₁)/N+ (f ₂-f ₁)/2N}, i=1,2,3 ... N adopts the rotation of coordinate numerical calculation method to produce frequency corresponding to described N Frequency point f _iSinusoidal waveform.

4. a kind of virtual image inhibition method according to claim 1, it is characterized in that: corresponding to the different scope of input signal frequency range, described virtual image inhibition method adopts optional low-pass filtering and bandpass filtering mode to carry out.

5. a kind of virtual image inhibition method according to claim 4 is characterized in that: when adopting the mode of low-pass filtering to carry out, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method only is selected N Frequency point f from the input signal frequency range _i

6. a kind of virtual image inhibition method according to claim 4 is characterized in that: when adopting the mode of bandpass filtering to carry out, the sinusoidal waveform frequency that produces by the rotation of coordinate numerical calculation method is selected N Frequency point f from the input signal frequency range _iWith band pass filter centre frequency f _cSum.

7. a virtual image suppresses circuit, by the described virtual image of claim 1 inhibition method input signal is carried out virtual image modulation, it is characterized in that: described circuit comprises the signal input part of processor, two-way and the signal output part of two-way, and what wherein be connected with complex coefficient on one road signal I/O path has limit for length's unit impulse response filter; First output of described processor is connected to sine-wave generator, and the signal input part of described sine-wave generator and two-way inserts frequency mixer in the lump, again via low pass or after being with logical filter, digital signal inserts described processor, and second output of described processor links to each other with the coefficient settings receiving terminal that limit for length's unit impulse response filter is arranged of complex coefficient.

8. a kind of virtual image according to claim 7 suppresses circuit, and it is characterized in that: described processor is at least system level chip, or the single-chip microcomputer of the equal data computation ability of tool.

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