CN110557122A - method for correcting frequency response non-uniformity error of TIADC system - Google Patents

Abstract

the invention discloses a sampling reconstruction filter bank-based TIADC system frequency response non-uniformity error correction method, which comprises the steps of firstly measuring the frequency response of each ADC of a TIADC system, then determining an ideal frequency response function, and calculating the frequency response of a sampling reconstruction filter by using the ideal frequency response and each ADC frequency response; obtaining the amplitude-frequency response and the group delay of the sampling reconstruction filter according to the frequency response of the sampling reconstruction filter, designing a first-stage linear phase amplitude-frequency compensation filter bank according to the amplitude frequency, designing a second-stage all-pass filter bank and a third-stage fractional delay filter bank according to the group delay, and calculating the integral delay, wherein the three filter banks form a sampling reconstruction filter bank; and finally, calculating a corrected sampling sequence according to the actual sampling sequence and the reconstructed sampling sequence, so that the problem of frequency response non-uniformity error correction of the TIADC system under large frequency response difference is solved.

Description

method for correcting frequency response non-uniformity error of TIADC system

Technical Field

The invention belongs to the technical field of time domain testing, and particularly relates to a TIADC system frequency response non-uniformity error correction method based on a sampling reconstruction filter bank.

Background

In the scheme of constructing the ultra-high-speed acquisition system, a time-interleaved adc (tiadc) architecture is widely applied due to its simple implementation. Using M slices with a sampling rate of f_sThe ADC of/M alternately samples the same signal in a time sequence with equal intervals, and the equivalent sampling rate f can be obtained_sthe sampled data of (1). Theoretically, when all ADCs are identical, the system and sampling rate is f_sThe single ADC acquisition system is equivalent to generate ideal sampling output.

However, in an actual TIADC system, the ADCs are not identical; furthermore, in order to sample the input signal by all ADCs, analog devices (such as power splitters) must be used to split the signal into multiple paths, which are subject to different deviations from the original signal via different transmission paths. The differences of the performance parameters of the analog devices, the transmission paths and the ADC cause the frequency response performance of each sampling path to be inconsistent, errors are inevitably introduced into sampling output, and the performance of the system is seriously degraded. In order to be able to bring the sampled output of the TIADC as close as possible to the ideal sampled output, the error has to be corrected.

in conventional TIADC error correction, the error is considered to be a combination of bias error, amplitude error and time error. Wherein the offset error is independent of the system frequency response, so the correction is mainly studied in terms of amplitude error and time error. The frequency response modeling of the mth channel is as follows:

Wherein g is_mAnd r_mThe gain error coefficient and the time error coefficient of the mth channel, respectively, are independent of the input signal frequency. A large number of patentsError estimation and correction methods are studied based on such error models. For example, patent CN106209103A uses spectrum analysis to analyze the sampled data of each channel ADC and perform error correction by the built-in correction unit of the ADC; patent CN107147392A uses an adaptive fractional delay filter for amplitude and time error correction. Common to these patents is that the error of the TIADC system is considered to be frequency-independent, i.e., the magnitude of the error is independent of the frequency of the input signal.

In a TIADC system, however, the nature of the error generation is to sample the difference in frequency response of each channel. That is, the difference between the respective sampling paths is not necessarily the same at different frequency points. This results in the errors generated by the TIADC system being not exactly the same for input signals of different frequencies, the errors being frequency dependent. Based on such consideration, patent CN108923784A and patent CN108809308A estimate full-bandwidth errors from amplitude and time, respectively, and correct the error at the point where the signal energy is maximum frequency by using the dot-frequency method, but this method still belongs to dot-frequency correction per se; patent US7978104 writes the frequency response of the sampling path in the form of a frequency domain polynomial and uses a polynomial filter for reconstruction, but this method is only suitable for the case of regular frequency response, and when the frequency response of the actual system is irregular, the frequency response of the sampling path is difficult to write in the form of a low-order polynomial, and the filter cannot be designed effectively.

In summary, there is no general method for correcting the TIADC frequency response non-uniformity error under the condition of large frequency response difference of the sampling channels. Therefore, it is very important to design a TIADC frequency response non-uniformity error correction method suitable for large channel frequency response differences.

Disclosure of Invention

the invention aims to overcome the defects of the prior art and provides a method for correcting frequency response non-uniformity errors of a TIADC system based on a sampling reconstruction filter bank, so that the error correction can still be carried out on the full bandwidth under the condition that the frequency response non-uniformity errors of the TIADC are large.

In order to achieve the above object, the present invention provides a method for correcting a frequency response inconsistency error of a TIADC system, which is characterized by comprising the following steps:

(1) designing a sampling reconstruction filter bank

(1.1) respectively measuring the frequency response of ADCs numbered from 0 to M-1 by using a dot frequency method or a broadband signal, wherein M is the number of ADCs in the TIADC system, and the mth ADC (namely the numbered ADC)_mIs noted as H_m(j ω), ω is the digital angular frequency;

(1.2) selecting ideal frequency response H_ideal(jω)；

filter design module selects ideal frequency response H_ideal(j ω) is the average of the frequency response of each channel, i.e.:

(1.3) calculating error reconstruction frequency response Q_m(jω)；

Q_m(jω)＝H_m(jω)/H_ideal(jω)

(1.4) calculating Q_mAmplitude-frequency response A of (j omega)_Qm(j ω) and group delay τ_m(ω)；

A_Qm(jω)＝|Q_m(jω)|

τ(ω)＝[arg(Q_m(j(ω+Δω)))-arg(Q_m(jω))]/Δω

wherein, | - | represents taking an absolute value, arg (·) represents taking a phase, and Δ ω represents a sampling interval of a frequency domain;

(1.5) designing an even-order linear phase amplitude-frequency compensation filter to enable amplitude-frequency response to be equal to A_Qm(j ω) group delay D_m1(ii) a Since the linear phase FIR order is even, D_m1Is an integer;

(1.6) designing an all-pass filter by using a complex cepstrum method to ensure that the group delay of the all-pass filter is equal to tau_m(ω)+D_m2Wherein D is_m2Is the overall extra delay introduced by designing an all-pass filter;

(1.7) designing a fractional delay FIR filter by utilizing a sinc function method to enable group delay to approachWherein the content of the first and second substances,Indicating rounding up, D_m3Is the overall extra delay introduced due to the design of the fractional delay filter;

(1.8) calculating the integral time delay of the channel filter;

(2) Correction of sampled data

(2.1) inputting the signal to be acquired into the TIADC system, and respectively obtaining N-point sampling sequences by each ADC, and recording the N-point sampling sequences as y_m(N), wherein N satisfies:

(2.2) sampling each path with a sequence y_m(n) splicing according to the sampling time sequence to obtain a spliced sequence y (n), and inputting y (n) into a FIFO (first in first out) for caching; while y (n) is input to the sample reconstruction filter bank.

(2.3) in each sampling reconstruction filter, a sampling sequence y (n) sequentially passes through an even-order linear phase amplitude-frequency compensation filter, an all-pass filter and a fractional delay FIR filter, and the reconstruction output of the m-th sampling reconstruction filter is set as y_Qm(n)；

(2.4) enabling the reading enable of the FIFO to be effective, then reading the sampling sequence y (n), and inputting the sampling sequence y (n) to the multiplier respectively;

(2.5) multiplying the read sampling sequence y (n) by a fixed coefficient 2 by a multiplier, and inputting the result to a subtracter;

(2.6) selecting a corresponding channel to output y by a data selector in the sampling reconstruction filter bank according to a source channel m of the current data of a read sampling sequence y (n)_Qm(n) to the subtractor. Setting the output sequence of the selected sampling reconstruction filter bank as y_Q(n)；

(2.7) calculating a corrected sampling value y by a subtracter_c(n)；

y_c(n)＝2·y(n)-y_Q(n)

(2.8) mixing_cAnd (n) sending the data to an upper computer for data caching and displaying, and finishing the frequency response non-uniformity error correction of the TIADC system.

the invention aims to realize the following steps:

The invention relates to a TIADC system frequency response non-uniformity error correction method based on a sampling reconstruction filter bank, which comprises the steps of firstly measuring the frequency response of each ADC of the TIADC system, then determining an ideal frequency response function, and calculating the frequency response of a sampling reconstruction filter by using the ideal frequency response and each ADC frequency response; obtaining the amplitude-frequency response and the group delay of the sampling reconstruction filter according to the frequency response of the sampling reconstruction filter, designing a first-stage linear phase amplitude-frequency compensation filter bank according to the amplitude frequency, designing a second-stage all-pass filter bank and a third-stage fractional delay filter bank according to the group delay, and calculating the integral delay, wherein the three filter banks form a sampling reconstruction filter bank; and finally, calculating a corrected sampling sequence according to the actual sampling sequence and the reconstructed sampling sequence, so that the problem of frequency response non-uniformity error correction of the TIADC system under large frequency response difference is solved.

meanwhile, the TIADC system frequency response non-uniformity error correction method based on the sampling reconstruction filter bank also has the following beneficial effects:

(1) by carrying out digital filtering and digital time alternation under the full sampling rate on the whole sampling, the problem that the frequency response non-uniformity error across a single ADC nano-domain is difficult to correct by the original TIADC error estimation and correction method is solved, and the TIADC frequency response non-uniformity error correction of the broadband signal becomes possible.

(2) And through the design of the compensation filter bank, the limitation of TIADC frequency response non-uniformity errors on ADC frequency response differences is relieved, and the frequency response non-uniformity errors under larger frequency response differences can be corrected.

Drawings

FIG. 1 is a schematic diagram of a 4-channel TIADC system frequency response non-uniformity error correction method based on a sampling reconstruction filter bank;

FIG. 2 is a schematic diagram of a TIADC system;

FIG. 3 is an equivalent system diagram of a TIADC;

FIG. 4 is another equivalent system diagram of a TIADC;

FIG. 5 is a schematic diagram of sample reconstruction in an ideal case;

FIG. 6 is a three-stage filter exploded view of a sample reconstruction filter;

FIG. 7 is a data correspondence of sampled data to filter reconstruction data;

Detailed Description

the following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.

Examples

FIG. 1 is a schematic diagram of a 4-channel TIADC system frequency response non-uniformity error correction method based on a sampling reconstruction filter bank.

In this embodiment, one M channel, with a sampling rate of f_sThe TIADC system of (a) is shown in fig. 2. Sampling rate of f_sADC of/M_mSimulating frequency response H by self-equivalent_m(j Ω), sampler and quantizer, and M is 0,1, …, M-1, Ω is the analog angular frequency. The input analog signal x (t) first passes through the ADC_mThe equivalent analog frequency response of (2); then in time series by the samplerSampling the signal, wherein the sampling interval T is 1/f_s(ii) a Finally, analog samples are converted into digital output y through a quantizer_m(k) In that respect Data recombination module arranges ADC in turn₀To ADC_M-1Digital output of, i.e.

where "n mod M" means that n is left over M,Indicating a rounding down.

If the sampling rate is f_sADC of/M_mEquivalent to a sampling rate of f_sADC (_emThen the equivalent system of the M-channel TIADC system shown in fig. 2 is shown in fig. 3.

At this time, the analog frequency response and quantizer of each equivalent ADC are not changed, except that each ADC is in time seriesThe signal is sampled. Let ADC_emis the equivalent output of y_em(n) then y_em(n) and y_m(k) The relationship between them is:

y_m(k)＝y_em(kM+m),k＝0,1,2,... (3)

thus, there are

y(n)＝y_{e(n mod M)}(n),n＝0,1,2,... (4)

The data selector selects the data of each channel in turn according to the formula (4) for recombination, and the whole process can be regarded as y_emAnd (n) sampling at different initial positions and then performing data reconstruction.

Since the ADC is at this time_emHas a sampling rate of f_sThus will simulate a frequency response H_m(j omega) conversion to a digital frequency response H_mNormalized frequency of f at (j ω)_sThe digital frequency response does not introduce spectral aliasing for analog signals that satisfy the nano-sampling condition of the TIADC system. ω is the digital angular frequency. H_m(j Ω) and H_mThe relationship between (j ω) is:

H_m(jω)＝H_m(jΩ/f_s),-π＜ω＜π (5)

The sampling time of the equivalent system is the same for all ADCs, and the data selector samples and recombines the sampling values in turn, so that the sampling time can be exchangedThe process of quantizing and passing through frequency response function of signal sample and using an ideal frequency response H_ideal(j ω) normalizing the ADC frequency responses, so that the original sampling output y (n) can be regarded as an ideal sampling signal x_ideal(n) and the error signal e (n). I.e., equivalent to the M-channel TIADC equivalent system shown in fig. 3, as shown in fig. 4.

The original signal x (t) is first in time seriesUp sampled and converted to a digital signal x (n) by a quantizer, after which the signal is split into two main paths. In path 1, x (n) passes through the ideal frequency response H_ideal(j ω) generating an ideal output signal x for the TIADC_ideal(n); in path 2, x (n) simultaneously passes through the error response E₀(j ω) to E_M-1(j ω) error e of each ADC is generated₀(n) to e_M-1(n), sequentially selecting errors corresponding to sampling output by the data selector according to the real sampling time of each ADC, and finally forming TIADC system errors e (n), namely

e(n)＝e_{(n mod M)}(n),n＝0,1,2,... (6)

Error frequency response E of mth channel_m(j ω), ideal frequency response H_ideal(j ω) and H_mThe relationship between (j ω) is:

E_m(jω)＝H_m(jω)-H_ideal(jω) (7)

Thus is provided with

e_m(n)＝y_em(n)-x_ideal(n),n＝0,1,2,... (8)

The actual sample output y (n) is the ideal sample x_ideal(n) and the sum of the errors e (n), i.e.

y(n)＝x_ideal(n)+e(n) (9)

To be able to reconstruct e (n), y (n) is split into two paths as shown in fig. 4. The first pass multiplies y (n) by a constant 2; the second path passes y (n) through the frequency response to Q_m(j ω) filter, wherein Q_m(j ω) and H_m(j ω) and H_idealThe relationship of (j ω) is:

Q_m(jω)＝H_m(jω)/H_ideal(jω) (10)

By the formula (9), y (n) is taken as x_idealThe sum of (n) and e (n). x is the number of_ideal(n) via Q_m(j ω) corresponds to x (n) passing through H_m(j ω), so the output is y_em(n) of (a). Let e (n) pass through H_mOutput after (j ω) is e'_m(n) of (a). Then after passing through the data selector, the output is

y_Q(n)＝y(n)+e'(n) (11)

The corrected sampling value y_c(n) is

y_c(n)＝2·y(n)-y_Q(n)＝x_ideal(n)+e(n)-e'(n) (12)

when selecting appropriate H_ideal(j ω) is, H_ideal(j ω) and H_m(j ω) approximation, Q_m(j ω) is close to constant 1, and therefore has

e'(n)≈e(n) (13)

If it holds that e' (n) is an approximate reconstruction of e (n), then

y_c(n)≈x_ideal(n) (14)

y_c(n) is x_ideal(n) approximate reconstruction.

As can be seen from the signal reconstruction process, the most critical problem in the whole process is the frequency response Q_mAnd (j ω) reconstructing. In order to enable the TIADC system to work with any input signal, it is necessary to construct a compensation filter system whose frequency response is able to approach Q continuously over the entire frequency band_m(j ω), i.e. should be equal in amplitude to Q_mthe amplitude of (j ω) remains the same while being aligned with Q over the group delay_mThe group delay found by (j ω) remains the same. However, for the TIADC system under large frequency response error, the approximation by using the traditional method (such as the least square method) cannot achieve good effect. The invention carries out three-level decomposition on the sampling reconstruction filter, and can continuously approximate Q from the frequency domain by using the three-level filter design method of the amplitude-frequency compensation filter, the all-pass filter and the fractional delay filter_m(j ω), ensuring the validity of the algorithm.

Assuming a frequency response Q_m(j ω) has an amplitude-frequency response of A_Qm(j ω) group delay τ_m(ω). Of the compensation filters, the amplitude-frequency compensation filter is a linear phase FIR filter for approximating A in amplitude-frequency response_Qm(j ω) during which an inherent group delay D is introduced due to the filter design_m1. Here, the order of the linear phase filter is controlled to D by using the characteristic of the filter_m1Are integers. All-pass filters for approximating tau at group delay_m(ω)+D_m2Wherein D is_m2Due to the overall additional delay introduced by the all-pass filter design, for input signal frequency D in all bandwidths_m2Are all the same. The fractional delay filter further compensates the group delay of the all-pass filter to make the total delay of the data be integer, i.e. the group delay of the fractional delay filter should beWhereindenotes rounding up, and D_m3Is the additional integer delay introduced due to the fractional delay filter design, for the input signal frequency D within all bandwidths_m3Are all the same. So that the correspondence in data is maintained with the sample values y (n). In summary, the overall integer delay D of the channel filter_mIs composed of

The sample reconstruction filter design is now complete, as shown in fig. 6.

suppose the reconstructed data after passing through the channel is y_Qm(n) then y (n) and y_QmThe delay relationship of (n) is shown in fig. 7. Thus, for the actual reconstruction data of the filter implementation, only D needs to be done in the output result_mThe reconstruction data corresponding to the original sampling data can be obtained by delaying the data, thereby meeting the correction requirement.

in this embodiment, as shown in fig. 1, we use a 4-channel TIADC system for detailed description, which specifically includes the following steps:

S1 design sampling reconstruction filter bank

s1.1, respectively measuring the frequency response of the ADCs with the numbers m of 0 to 3 by using a dot frequency method or a broadband signal, wherein the mth ADC, namely the numbered ADC_mis noted as H_m(j ω), ω is the digital angular frequency;

In this embodiment, a relative frequency response function of the channel within the bandwidth is obtained by using a dot frequency method, a relative amplitude-frequency curve of the channel at each dot frequency can be obtained by patent CN108923784A, and a relative phase-frequency curve of each dot frequency can be obtained by patent CN 108809308A. Let ADC_mhas a frequency response of H_m(j ω). Wherein m is 0,1,2, 3. In the process of measuring the frequency response, the flow direction of the collected data is as follows: ADC-data receiving module-data splicing module-FIFO-data selecting module-upper computer. And the upper computer calculates the frequency response of each channel by using an FFT and frequency response calculation module.

s1.2, selecting ideal frequency response H_ideal(jω)；

Filter design module selects ideal frequency response H_ideal(j ω) is the average of the frequency response of each channel, i.e.:

s1.3, calculating error reconstruction frequency response Q_m(jω)；

Q_m(jω)＝H_m(jω)/H_ideal(jω)

s1.4, calculating Q_mAmplitude-frequency response A of (j omega)_QmGroup delay τ of (j ω)_m(ω)；

A_Qm(jω)＝|Q_m(jω)|

τ(ω)＝[arg(Q_m(j(ω+Δω)))-arg(Q_m(jω))]/Δω

Wherein, | - | represents taking an absolute value, arg (·) represents taking a phase, and Δ ω represents a sampling interval of a frequency domain;

S1.5, designing an even-order linear phase amplitude-frequency compensation filter to enable amplitude-frequency response to be equal to A_Qm(j ω) group delay ofD_m1(ii) a Since the linear phase FIR order is even, D_m1Is an integer;

S1.6, designing an all-pass filter by using a complex cepstrum method to enable group delay of the all-pass filter to be equal to tau_m(ω)+D_m2wherein D is_m2is the overall extra delay introduced by designing an all-pass filter;

S1.7, designing a fractional delay FIR filter by utilizing a sinc function method to enable group delay to approachWherein the content of the first and second substances,Indicating rounding up, D_m3Is the overall extra delay introduced due to the design of the fractional delay filter;

S1.8, calculating the integral time delay of the channel filter;

S2, correction of sampling data

s2.1, inputting the signal to be acquired into the TIADC system, and respectively obtaining N-point sampling sequences by each ADC, and recording the N-point sampling sequences as y_m(N), wherein N satisfies:

s2.2, sampling each path of sequence y_m(n) splicing according to the sampling time sequence to obtain a spliced sequence y (n), and inputting y (n) into a FIFO (first in first out) for caching; simultaneously inputting y (n) to a sample reconstruction filter bank;

S2.3, in each sampling reconstruction filter, a sampling sequence y (n) sequentially passes through an even-order linear phase amplitude-frequency compensation filter, an all-pass filter and a fractional delay FIR filter, and the reconstruction output of the mth sampling reconstruction filter is set as y_Qm(n)；

s2.4, enabling the read enable of the FIFO to be effective, then reading the sampling sequence y (n), and inputting the sampling sequence y (n) to a multiplier respectively;

s2.5, multiplying the read sampling sequence y (n) by a fixed coefficient 2 by a multiplier, and inputting the result into a subtracter;

S2.6, selecting a corresponding channel to output y by a data selector in the sampling reconstruction filter bank according to a source channel m of reading sampling sequence y (n) current data_Qm(n) to the subtractor. Setting the output sequence of the selected sampling reconstruction filter bank as y_Q(n)；

S2.7, calculating a correction sampling value y by utilizing a subtracter_c(n)；

y_c(n)＝2·y(n)-y_Q(n)

S2.8, mixing y_cAnd (n) sending the data to an upper computer for data caching and displaying, and finishing the frequency response non-uniformity error correction of the TIADC system.

Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.

Claims (1)

1. A TIADC system frequency response non-uniformity error correction method based on an error reconstruction filter bank is characterized by comprising the following steps:

(1) Designing a sampling reconstruction filter bank

(1.1) respectively measuring the frequency response of ADCs (analog to digital converter) numbered from 0 to M-1 by using a dot frequency method or broadband signals, wherein M is the number of ADCs in the TIADC system, and the mth ADC_mIs noted as H_m(j ω), ω is the digital angular frequency;

(1.2) selecting ideal frequency response H_ideal(jω)；

Filter design module selects ideal frequency response H_ideal(j ω) is the average of the frequency response of each channel, i.e.:

(1.3) calculating error reconstruction frequency response Q_m(jω)；

Q_m(jω)＝H_m(jω)/H_ideal(jω)

(1.4) calculating Q_mAmplitude-frequency response A of (j omega)_Qm(j ω) and group delay τ_m(ω)；

A_Qm(jω)＝|Q_m(jω)|

τ(ω)＝[arg(Q_m(j(ω+Δω)))-arg(Q_m(jω))]/Δω

Wherein, | - | represents taking an absolute value, and arg (·) represents taking a phase;

(1.5) designing an even-order linear phase amplitude-frequency compensation filter to make the amplitude-frequency response equal to A_Qm(j ω) group delay D_m1(ii) a Since the linear phase FIR order is even, D_m1Is an integer;

(1.6) designing an all-pass filter by using a complex cepstrum method to ensure that the group delay of the all-pass filter is equal to tau_m(ω)+D_m2wherein D is_m2Is the overall extra delay introduced by designing an all-pass filter;

(1.7) designing a fractional delay FIR filter by utilizing a sinc function method to enable group delay to approachWherein the content of the first and second substances,Indicating rounding up, D_m3Is the overall extra delay introduced due to the design of the fractional delay filter;

(1.8) calculating the integral time delay of the channel filter;

(2) Correction of sampled data

(2.1) inputting the signal to be acquired into the TIADC system, and respectively obtaining N-point sampling sequences by each ADC, and recording the N-point sampling sequences as y_m(N), wherein N satisfies:

(2.2) sampling each path with a sequence y_m(n) splicing according to the sampling time sequence to obtain a spliced sequence y (n), and inputting y (n) into a FIFO (first in first out) for caching; simultaneously inputting y (n) to a sample reconstruction filter bank;

(2.3) in each sampling reconstruction filter, the sampling sequence y (n) sequentially passes through an even-order linear phase amplitude-frequency compensation filter, an all-pass filter and a fractional delay FIR filter, wherein the reconstruction output of the m-th sampling reconstruction filter is y_Qm(n)；

(2.4) enabling the reading enable of the FIFO to be effective, then reading the sampling sequence y (n), and inputting the sampling sequence y (n) to the multiplier respectively;

(2.5) multiplying the read sampling sequence y (n) by a fixed coefficient 2 by a multiplier, and inputting the result to a subtracter;

(2.6) selecting a corresponding channel to output y by a data selector in the sampling reconstruction filter bank according to a source channel m of the current data of a read sampling sequence y (n)_Qm(n) to the subtracter, and the output sequence of the selected sampling reconstruction filter bank is set as y_Q(n)；

(2.7) calculating a corrected sampling value y by a subtracter_c(n)；

y_c(n)＝2·y(n)-y_Q(n)

(2.8) mixing_cAnd (n) sending the data to an upper computer for data caching and displaying, and finishing the frequency response non-uniformity error correction of the TIADC system.