CN101212436B - High pass filter frequency response characteristic compensator and method and zero intermediate frequency receiver - Google Patents

Abstract

The invention discloses a device for compensating frequency response characteristic of a high-pass filter and a method thereof as well as a zero-if receiver; wherein the device for compensating frequency response characteristic of the high-pass filter consists of an A/D conversion module respectively connected with the corresponding high-pass filter, which is used for converting a signal after the high-pass filter filters a DC shift into a digital signal and outputting the digital signal; a digital compensation filter used for receiving the outputted signal of the A/D conversion module to carry out digital signal processing; a 3dB cutoff frequency of an equivalent high-pass filter formed by combination of the digital compensation filter and the high-pass filter is lower than that of the high-pass filter. By using the invention, effect of the system on a useful signal can be effective minished.

Description

The compensation arrangement of the Frequency Response of high pass filter and method and zero intermediate frequency reciver

Technical field

The present invention relates to zero intermediate frequency reciver, particularly the compensation arrangement of the frequency response characteristic of high pass filter and method in the zero intermediate frequency reciver.

Background technology

In the zero intermediate frequency reciver framework, as shown in Figure 1, because local oscillation signal LO can be leaked to the radio-frequency (RF) signal input end mouth of frequency mixer, cause the self-mixing phenomenon, produced direct current offset, and this direct current biasing will cause that thereby ADC is saturated to cause serious distorted signals, and therefore (before the ADC) must suppress direct current offset when the back level is handled, and common way is to use high pass filter.

As shown in Figure 1, existing employing high pass filter carries out comprising in the zero intermediate frequency reciver that direct current offset suppresses:

Low noise amplifier (Low Noise Amplifier, LNA);

The frequency mixer of a pair of relation of being orthogonal, be used for received signal down-convert to a pair of on in-phase signal path and orthogonal signalling path will be by the orthogonal signalling of demodulation, wherein, received signal is by mixing the realization down-conversion with local oscillation signal LO;

High pass filter is used for the target signal filter direct current offset after the down-conversion;

Low pass filter and AGC are used for the down-conversion signal behind the filtering direct current offset is carried out being divided into I road and the output of Q road after the respective handling.

Yet shown in Figure 1 comprising is used for suppressing the zero intermediate frequency reciver of the high pass filter of direct current offset, high pass filter in the filtering direct current offset filtering a part of useful signal.

The 3dB frequency f of high pass filter _cWith signal bandwidth f _dCompare, the big more deterioration degree to signal quality of ratio is big more, can use Error Vector Magnitude (EVM) to weigh at this signal quality.That is to say that the Frequency Response of high pass filter has had a strong impact on the EVM of received signal.

In real system, high pass filter 3dB frequency f _cLow more, the stabilization time that its rank respond more is also long more, yet, because the mode of analog filter, 3dB frequency f are adopted in the realization of high pass filter more _cLow more, realize that cost is high more, so in the real system, high pass filter 3dB frequency f _cGenerally about 10kHz.

Simultaneously, can find,, work as f for the ideal signal of spreading rate 1.28MHz QPSK modulation by emulation and actual test _c=8.7kHz, influence can reach about 20% to EVM.

Because the frequency response of high pass filter has had a strong impact on the EVM of signal, and EVM is big more, the signal to noise ratio of output signal is more little.Adopting high-order modulating, the demanding system of output signal-to-noise ratio as adopting the HSDPA system of 16QAM modulation system, can have a strong impact on the throughput of system.

Therefore be necessary the frequency response of high pass filter is compensated, reduce its influence useful signal.

Summary of the invention

The object of the present invention is to provide a kind of compensation arrangement and method of Frequency Response of high pass filter, reduce high pass filter influence to useful signal when carrying out the filtering direct current offset, guarantee the throughput of system.

To achieve these goals, the invention provides a kind of compensation arrangement of Frequency Response of high pass filter, wherein, comprising:

The A/D modular converter connects with corresponding high pass filter respectively, and being used for the conversion of signals behind the high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, the output signal that is used to receive the A/D modular converter is carried out Digital Signal Processing;

Combine with the high pass filter 3dB cut-off frequency of the equivalent high pass filter that forms of described digital compensation filter is lower than the 3dB cut-off frequency of described high pass filter.

Above-mentioned compensation arrangement wherein, also comprises:

The direct current offset cancellation module be used for amplifying at the nearly zero-frequency direct current offset that numeric field is eliminated by digital compensation filter brought, and nearly zero-frequency direct current offset amplifying signal has been eliminated in output.

Above-mentioned compensation arrangement, wherein, described direct current offset cancellation module specifically comprises:

Original sampling data sequence acquisition module is used for obtaining a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

The second data sequence acquisition module is used for described original sampling data sequence is asked on average every the data point of first number, and gives data point corresponding in the original sampling data sequence with this mean value that obtains assignment again, obtains second data sequence;

The 3rd data sequence acquisition module is exported after being used for the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence.

In order better to realize above-mentioned purpose, the present invention also provides a kind of compensation method of Frequency Response of high pass filter, wherein, comprising:

The A/D switch process carries out A/D conversion back output with the output signal of high pass filter;

The numeric field compensation process utilizes a digital compensation filter to carry out Digital Signal Processing the signal after the A/D conversion; Described digital compensation filter combines the 3dB cut-off frequency of the equivalent high pass filter that forms less than the 3dB cut-off frequency of described high pass filter with described high pass filter.

Above-mentioned compensation method wherein, also comprises:

The direct current removal process is eliminated the nearly zero-frequency direct current offset that is brought by the digital compensation step at numeric field and is amplified.

Above-mentioned compensation method, wherein, described direct current removal process specifically comprises:

Obtain a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

Described original sampling data sequence is asked on average every the data point of first number, and will be obtained second data sequence after the data point of this mean value that obtains assignment again to correspondence in the original sampling data sequence;

Export after the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence.

In order better to realize above-mentioned purpose, the present invention also provides a kind of zero intermediate frequency reciver, comprises the frequency mixer and the high pass filter of low noise amplifier, a pair of relation of being orthogonal, and wherein, also comprises:

The A/D modular converter connects with corresponding high pass filter respectively, and being used for the conversion of signals behind the high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, the output signal that is used to receive the A/D modular converter is carried out Digital Signal Processing;

Combine with the high pass filter 3dB cut-off frequency of the equivalent high pass filter that forms of described digital compensation filter is lower than the 3dB cut-off frequency of described high pass filter.

Above-mentioned zero intermediate frequency reciver wherein, also comprises:

The direct current offset cancellation module be used for amplifying at the nearly zero-frequency direct current offset that numeric field is eliminated by digital compensation filter brought, and nearly zero-frequency direct current offset amplifying signal has been eliminated in output.

Above-mentioned zero intermediate frequency reciver, wherein, described direct current offset cancellation module specifically comprises:

Original sampling data sequence acquisition module is used for obtaining a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

The second data sequence acquisition module is used for described original sampling data sequence is asked on average every the data point of first number, and gives data point corresponding in the original sampling data sequence with this mean value that obtains assignment again, obtains second data sequence;

The 3rd data sequence acquisition module is exported after being used for the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence.

The compensation arrangement of the Frequency Response of high pass filter of the present invention, compensation method and zero intermediate frequency reciver are by being provided with a digital compensation filter at numeric field, reduce the 3dB cut-off frequency of equivalent high pass filter, therefore effectively reduced influence to useful signal, by utilizing direct current skew cancellation module to eliminate, therefore further reduced influence simultaneously to useful signal because the nearly zero-frequency direct current offset that digital compensation filter is introduced amplifies.

Description of drawings

Fig. 1 is the brief configuration schematic diagram of the zero intermediate frequency reciver of existing band high pass filter;

Fig. 2 is the structural representation of compensation arrangement of the Frequency Response of high pass filter of the present invention;

Fig. 3 is the flow chart of compensation method of the Frequency Response of high pass filter of the present invention.

Embodiment

The compensation arrangement of the Frequency Response of high pass filter of the present invention and method, and in the corresponding zero intermediate frequency reciver, by this compensation arrangement is set, make it to combine the high pass filter of formation one equivalence with original high pass filter, the 3dB cut-off frequency of this equivalence high pass filter is lower than the 3dB cut-off frequency of high pass filter, therefore when reducing signal processing to the influence of useful signal.

The compensation arrangement of the Frequency Response of high pass filter of the present invention specifically comprises as shown in Figure 2:

Two A/D modular converters connect with corresponding high pass filter respectively, and the conversion of signals that is used for high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, being used for combining with high pass filter forms the high pass filter of an equivalence, and the 3dB cut-off frequency of the high pass filter that this is equivalent is lower than the 3dB cut-off frequency of high pass filter.

The front is mentioned, existing high pass filter is an analog filter, if on existing basis, reduce the 3dB cut-off frequency, the adverse consequences that can cause cost sharply to promote, therefore in the compensation arrangement of the present invention, after at first the conversion of signals of high pass filter being digital signal, utilize digitized compensating filter to handle by two A/D modular converters.

Design to the digital compensation filter in the compensation arrangement of the Frequency Response of high pass filter of the present invention is elaborated below.

The transfer function of existing high pass filter is known, is assumed to be H at this _I(s), wherein comprise the parameter relevant in this transfer function with the 3dB cut-off frequency.

As transfer function $H\left(s\right)=\frac{s^3}{{(s+a)}^3},$ Its 3dB is by being $\frac{a}{2\·\mathrm{\π}}\sqrt{\frac{1}{2^{\frac{1}{3}}-1}}.$

At this, be lower than the 3dB cut-off frequency of high pass filter for the 3dB cut-off frequency of the equivalent high pass filter behind the feasible increase digital compensation filter, then only need the transfer function of equivalent high pass filter identical with the structure of the transfer function of high pass filter, the parameter relevant with the 3dB cut-off frequency can be set the 3dB cut-off frequency of equivalent high pass filter in the transfer function of the equivalent high pass filter of corresponding simultaneously adjustment.

At this, the transfer function of supposing equivalent high pass filter is H _O(s), the transfer function of digital compensation filter is H (s), because H _O(s)=H _I(s) H (s), therefore:

H(s)＝H _O(s)/H _I(s)

Can obtain the structure of corresponding digital compensating filter under the situation that transfer function is determined,, not repeat them here because our department is divided into those of ordinary skills and does not need creative work to realize.

After yet the present invention utilizes digital compensation filter to reduce the 3dB cut-off frequency of equivalent high pass filter, yet the direct current offset of nearly zero-frequency is amplified again, therefore, further comprise in the compensation arrangement of the Frequency Response of high pass filter of the present invention:

The direct current offset cancellation module be used for eliminating by the direct current offset that digital compensation filter brought at numeric field, and nearly zero-frequency direct current offset amplifying signal has been eliminated in output.

Below above-mentioned direct current offset cancellation module is described in more detail.

The direct current offset cancellation module specifically comprises:

Original sampling data sequence acquisition module is used for obtaining a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

The second data sequence acquisition module is used for described original sampling data sequence is asked on average every the data point of first number, and gives data point corresponding in the original sampling data sequence with this mean value that obtains assignment again, obtains second data sequence;

The 3rd data sequence acquisition module is exported after being used for the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence.

The detailed operation process of direct current offset cancellation module is as described below:

At first sampling obtains a time-limited data sequence from the output sequence of digital compensation filter, and at this called after x (n), wherein 0≤n≤N-1 for simplicity, supposes N=M (d+1), and d is an integer;

Then, the every M of the data sequence of this a sampling data point is asked once average, and give corresponding data point, obtain new data sequence x this mean value that obtains assignment again _k(n);

At last, sample sequence x (n) is deducted respective x successively _k(n) obtain the output of new data sequence y (n) back, this data sequence y (n) has eliminated the influence of direct current offset.

Only proposed the implementation of the influence of cancellation of DC offset above, how not selected M to realize cancellation of DC offset, will be described in detail this part below but provide.

Finite length sequence: x (n), 0≤n≤N-1, its DFT (two-dimensional Fourier transform) is transformed to:

$X\left[k\right]=\left\{\begin{array}{c}\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(n\right)W_N^{\mathrm{kn}},0\≤k\≤N-1\\ 0,\mathrm{else}\end{array}---\left(1\right)\right.$

Wherein, W _N=e ^{-j (2 π/N)}, at this, the description of subsequent calculations process for convenience is at this supposition N/M=d+1.

The every M of the data sequence of this a sampling data point is asked once average, and gives the data sequence that obtains after the corresponding data point as follows this mean value that obtains assignment again:

$x_e\left(n\right)=\frac{1}{M}\{\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)[u\left(n\right)-u(n-M)]+$

$\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)[u(n-M)-u(n-2M)]+\·\·\·\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)[u(n-\mathrm{dM})-u(n-N)]\}$

Above-mentioned data sequence is carried out can obtaining after the Fourier transform:

$X_e\left[k\right]=\frac{1}{N}\frac{1}{M}[\underset{n=0}{\overset{M-1}{\mathrm{\Σ}}}{W}_N^{\mathrm{kn}}\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+\underset{n=M}{\overset{2M-1}{\mathrm{\Σ}}}{W}_N^{\mathrm{kn}}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·\underset{n=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}{W}_N^{\mathrm{kn}}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

$=\frac{1}{N}\frac{1}{M}[\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+W_N^{\mathrm{kM}}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·W_N^{\mathrm{kdM}}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

$=\frac{1}{N}\frac{1}{M}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}[\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+W_N^{\mathrm{kM}}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·W_N^{\mathrm{kdM}}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

The front is mentioned, and the direct current offset cancellation module is last, and sample sequence x (n) is deducted respective x successively _k(n) obtain the output of new data sequence y (n) back, that is: y (n)=x (n)-x _e(n), therefore:

$Y\left[k\right]=\frac{1}{N}\underset{i=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)W_N^{\mathrm{ki}}-\frac{1}{N}\frac{1}{M}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}[\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+W_N^{\mathrm{kM}}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·W_N^{\mathrm{kdM}}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

$=X\left(k\right)-\frac{1}{N}\frac{1}{M}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}\mathrm{ES}\left(k\right)$

Wherein: $\mathrm{ES}\left(k\right)=[\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+W_N^{\mathrm{kM}}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·W_N^{\mathrm{kdM}}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

When signal x (n) is random signal, then

$\frac{\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)}{M}=\frac{\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)}{M}=\·\·\·=\frac{\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)}{M}=X\left(0\right)$

Therefore:

$Y\left[k\right]=\frac{1}{N}\underset{i=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)W_N^{\mathrm{ki}}-\frac{1}{N}\frac{1}{M}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}[\underset{i=0}{\overset{M-1}{\mathrm{\Σ}}}x\left(i\right)+W_N^{\mathrm{kM}}\underset{i=M}{\overset{2M-1}{\mathrm{\Σ}}}x\left(i\right)+\·\·\·W_N^{\mathrm{kdM}}\underset{i=\mathrm{dM}}{\overset{N-1}{\mathrm{\Σ}}}x\left(i\right)]$

$=X\left(k\right)-\frac{1}{N}\frac{1-W_N^{\mathrm{kM}}}{1-W_N^k}\left(0\right)*\frac{1-W_N^{\mathrm{kdM}}}{1-W_N^{\mathrm{kM}}}=X\left(k\right)-X\left(0\right)\frac{1}{N}\frac{1-W_N^{\mathrm{kdM}}}{1-W_N^k}$

Its transfer function is by M, and N and X (0) determine, under the situation of selecting certain N, can determine the numerical value of this M according to the degree of the required cancellation of DC offset of direct current offset cancellation module.

As shown in Figure 3, the compensation method of the Frequency Response of high pass filter of the present invention comprises the steps:

The A/D switch process carries out the A/D conversion with the output signal of high pass filter;

The numeric field compensation process obtains the signal after A/D changes, and utilizes a digital compensation filter to carry out signal processing; The 3dB cut-off frequency of described digital compensation filter and the formed equivalence filter of described high pass filter is less than the 3dB cut-off frequency of described high pass filter;

The direct current removal process is eliminated the nearly zero-frequency direct current offset that is brought by the digital compensation step at numeric field and is amplified.

Wherein, this direct current removal process specifically comprises:

Obtain a time-limited original sampling data sequence;

Described original sampling data sequence is asked on average every the data point of first number, and given data point corresponding in the original sampling data sequence, obtain second data sequence this mean value that obtains assignment again;

Export after the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence.

Zero intermediate frequency reciver of the present invention comprises:

Reception antenna;

Low noise amplifier (Low Noise Amplifier, LNA);

The frequency mixer of a pair of relation of being orthogonal, be used for received signal down-convert to a pair of on in-phase signal path and orthogonal signalling path will be by the orthogonal signalling of demodulation, wherein, received signal is by mixing the realization down-conversion with local oscillation signal LO;

High pass filter is used for the target signal filter direct current offset after the down-conversion;

Low pass filter and AGC are used for the down-conversion signal behind the filtering direct current offset is carried out being divided into I road and the output of Q road after the respective handling;

Wherein, also comprise the compensation arrangement as shown in Figure 2 that is connected in high frequency filter, this compensation arrangement specifically comprises:

Two A/D modular converters connect with corresponding high pass filter respectively, and the conversion of signals that is used for high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, being used for combining with high pass filter forms the high pass filter of an equivalence, and the 3dB cut-off frequency of the high pass filter that this is equivalent is lower than the 3dB cut-off frequency of high pass filter.

Simultaneously, this zero intermediate frequency reciver also can comprise the direct current offset cancellation module, owing to be described in detail in front, does not repeat them here.

The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (6)

1. the compensation arrangement of the Frequency Response of a high pass filter is characterized in that, comprising:

The A/D modular converter connects with corresponding high pass filter respectively, and being used for the conversion of signals behind the high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, the output signal that is used to receive the A/D modular converter is carried out Digital Signal Processing;

Combine with the high pass filter 3dB cut-off frequency of the equivalent high pass filter that forms of described digital compensation filter is lower than the 3dB cut-off frequency of described high pass filter;

The direct current offset cancellation module be used for amplifying at the nearly zero-frequency direct current offset that numeric field is eliminated by digital compensation filter brought, and nearly zero-frequency direct current offset amplifying signal has been eliminated in output.

2. compensation arrangement according to claim 1 is characterized in that, described direct current offset cancellation module specifically comprises:

Original sampling data sequence acquisition module is used for obtaining a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

The second data sequence acquisition module is used for described original sampling data sequence is asked on average every the data point of first number, and gives data point corresponding in the original sampling data sequence with this mean value that obtains assignment again, obtains second data sequence;

The 3rd data sequence acquisition module is exported after being used for the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence, and the 3rd data sequence is to have eliminated nearly zero-frequency direct current offset amplifying signal.

3. the compensation method of the Frequency Response of a high pass filter is characterized in that, comprising:

The A/D switch process carries out A/D conversion back output with the output signal of high pass filter;

The numeric field compensation process utilizes a digital compensation filter to carry out Digital Signal Processing the signal after the A/D conversion; Described digital compensation filter combines the 3dB cut-off frequency of the equivalent high pass filter that forms less than the 3dB cut-off frequency of described high pass filter with described high pass filter; And

The direct current removal process is eliminated the nearly zero-frequency direct current offset that is brought by the digital compensation step at numeric field and is amplified.

4. compensation method according to claim 3 is characterized in that, described direct current removal process specifically comprises:

Obtain a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

Described original sampling data sequence is asked on average every the data point of first number, and will be obtained second data sequence after the data point of this mean value that obtains assignment again to correspondence in the original sampling data sequence;

Export after the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence, the 3rd data sequence is to have eliminated nearly zero-frequency direct current offset amplifying signal.

5. a zero intermediate frequency reciver comprises low noise amplifier, a pair of frequency mixer and the high pass filter that is orthogonal and concerns, it is characterized in that, also comprises:

The A/D modular converter connects with corresponding high pass filter respectively, and being used for the conversion of signals behind the high pass filter filtering direct current offset is to export after the digital signal;

Digital compensation filter, the output signal that is used to receive the A/D modular converter is carried out Digital Signal Processing;

Combine with the high pass filter 3dB cut-off frequency of the equivalent high pass filter that forms of described digital compensation filter is lower than the 3dB cut-off frequency of described high pass filter;

The direct current offset cancellation module be used for amplifying at the nearly zero-frequency direct current offset that numeric field is eliminated by digital compensation filter brought, and nearly zero-frequency direct current offset amplifying signal has been eliminated in output.

6. zero intermediate frequency reciver according to claim 5 is characterized in that, described direct current offset cancellation module specifically comprises:

Original sampling data sequence acquisition module is used for obtaining a time-limited original sampling data sequence from the output signal sampling of digital compensation filter;

The second data sequence acquisition module is used for described original sampling data sequence is asked on average every the data point of first number, and gives data point corresponding in the original sampling data sequence with this mean value that obtains assignment again, obtains second data sequence;

The 3rd data sequence acquisition module is exported after being used for the original sampling data sequence deducted the 3rd data sequence that obtains after second data sequence, and the 3rd data sequence is to have eliminated nearly zero-frequency direct current offset amplifying signal.

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