CN101674087A - Method for obtaining channel mismatching error of time alternative ADC system - Google Patents

Abstract

The invention discloses a method for obtaining channel mismatching error of a time alternative ADC system; the time alternative ADC system samples a sine-input signal x(t) to obtain the actual outputsequence Yi equaling to yi<0>, yi<1>, and the like, yi<N minus 1> of each channel, wherein i is equal to 0, 1, and the like, M minus 1; a certain channel s selected as a reference channel and an interpolation function is used for interpolating the actual output sequence thereof to obtain the output sequence without mismatching error of rest channels relative to the reference channel; a sine fitting method is respectively adopted to fit the output sequence without mismatching error of the rest channels and the actual output sequence; and the mismatching error of the rest channels relative to the reference channel is obtained according to the sampling model yi<n> equaling to gi multiplied by (nMT<s> plus iT<s> plus Delta t<i>) plus os<i> of the time alternative ADC system. The purposes of the invention are realized by adopting interpolation and sine fitting in the method for obtaining channel mismatching error of a time alternative ADC system; moreover, gain, deflection and time delay errors are considered, thus guaranteeing the precision of the obtained channel mismatching error.

Description

A kind of acquisition methods of channel mismatching error of time alternative ADC system

Technical field

The present invention relates to high-speed, high precision Sampling techniques field, specifically, relate to a kind of acquisition methods of channel mismatching error of time alternative ADC system.

Background technology

Many digital signal processing appts as radar base station or VDSL modulator-demodulator, need analog to digital converter (ADC) to have higher sampling rate.In order to obtain sufficiently high sample rate, can adopt time alternative ADC (TIADC) system to realize.

Time alternative ADC system is made of the ADC sampling channel that the M group is parallel to each other, each ADC operating frequency is the 1/M of the total sample frequency of TIADC system, mode with alternating sampling is sampled to input signal, therefore, the M that the sampling rate of TIADC system can reach the high sampling rate of single channel ADC doubly, this method can improve the sample rate of analog to digital converter simply and effectively.

Yet if does not wait at the interval between the TIADC system neighbouring sample point, when promptly each channel clock postponed not match, the output of system can produce error.When frequency input signal is systematic sampling rate one half, be in half of least significant bit (LSB) (LSB) with this ERROR CONTROL, then the error in sampling interval must be lower than the sampling period (π 2 ⁿ) ^-1Doubly, wherein n is the sampling system number of significant digit, and such as the system for a 6bit, the error in sampling interval must be lower than 0.5% of the sampling period, and when sample frequency was 4GHz, this error must be controlled in 1.2 psecs.

Except the clock delay mismatch error, gain between each passage of TIADC system and skew mismatch error also are that error is introduced in the output of system.Gain, skew and clock mismatch error are to the influence of TIADC system output, show on the output spectrum it then is the distortion spectrum that produces except that frequency input signal, this class distortion spectrum has reduced the Spurious Free Dynamic Range (SFDR) of TIADC system, makes the resolution of TIADC system be lower than single channel ADC.

If can calculate the mismatch error of each passage of TIADC system, just can calibrate or compensate the dateout of each passage according to these errors, reduce mismatch error, reduce the output spectrum distortion, improve the SFDR of system.The acquisition methods of present most mismatch errors all is to set up on one or both the basis in ignoring gain, skew and clock delay mismatch error, and just there is error in the mismatch error of obtaining by these methods itself; In addition, some acquisition methods also needs the cooperation of additional circuit such as digital filter just can finish, and the adding of additional circuit not only can bring new error, and can't obtain the mismatch error of ultrahigh speed TIADC system channel.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of acquisition methods of more precise time alternative ADC system channel mismatching error is provided.

For achieving the above object, the acquisition methods of channel mismatching error of time alternative ADC system of the present invention may further comprise the steps:

(1), producing frequency with sinusoidal signal generator is f _InSinusoidal input signal x (t), time alternative ADC system is sampled to this sinusoidal input signal x (t), obtains the actual output sequence Y of each passage _i=[y _i[0], y _i[1] ..., y _i[N-1]] i=0,1...M-1, wherein, M is the port number of time alternative ADC system;

(2), to choose certain passage be reference channel, utilizes interpolating function to its actual output sequence interpolation, obtains rest channels does not have mismatch error with respect to reference channel output sequence;

(3), output sequence and actual output sequence that rest channels is not had a mismatch error adopt sinusoidal fitting process to carry out match respectively, constructs the output sequence sinusoidal expression and the actual output sequence sinusoidal expression of no mismatch error of the rest channels of match;

(4), there are not the output sinusoidal expression of mismatch error and the sampling model y of actual output sinusoidal expression and time alternative ADC system according to the rest channels of match _i[n]=g _iX (nMT _s+ iT _s+ Δ t _i)+os _i, obtain the mismatch error of rest channels, wherein g with respect to reference channel _i, Δ t _iAnd c _iThe gain, the sampling clock that are respectively time alternative ADC system i passage postpone and skew T _sBe the sampling period of time alternative ADC system.

The object of the present invention is achieved like this, adopts interpolation, sinusoidal match in the acquisition methods of channel mismatching error of time alternative ADC system, and considered gain, skew and clock delay error, guaranteed the precision of the channel mismatching error of acquisition; Interpolation to the reference channel sequence adopts interpolating function to carry out, and does not need actual filtering interpolation circuit, has guaranteed the accuracy of interpolating sequence, and can not introduce new error; Directly the time alternative ADC system output sequence of storing is handled, do not needed the taking into account system operating rate, therefore can measure the ultrahigh speed time alternative ADC system; Need in time alternative ADC system, not add extra circuit, except that having reduced overhead, also make obtaining of channel mismatching error of time alternative ADC system that this method can be used for having designed, and can not introduce new error, reached the purpose of accurate measurement.

Description of drawings

Fig. 1 is the electric theory diagram under a kind of embodiment of the acquisition methods of channel mismatching error of time alternative ADC system of the present invention;

Fig. 2 is the sampling model of i ADC passage of time alternative ADC system shown in Figure 1;

Fig. 3 is a time alternative ADC system shown in Figure 1 when having quantization error, the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error;

Fig. 4 is a time alternative ADC system shown in Figure 1 when having quantization error and passage random error, the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error;

Fig. 5 is that the sinusoidal input signal that sinusoidal signal generator shown in Figure 1 produces comprises harmonic distortion, when time alternative ADC system exists quantization error and passage random error, and the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error;

Fig. 6 be the channel mismatching error that obtains according to the present invention to the output waveform figure before and after the high-speed digitization instrument passage output calibration, wherein, Fig. 6 a is the output waveform figure when not calibrating, Fig. 6 b is the output waveform figure after the calibration.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described, so that understand the present invention better.What need point out especially is that in the following description, when perhaps the detailed description that adopts known function and design can desalinate main contents of the present invention, these were described in here and will be left in the basket.

Embodiment

Fig. 1 is the electric theory diagram under a kind of embodiment of the acquisition methods of channel mismatching error of time alternative ADC system of the present invention

In the present embodiment, as shown in Figure 1, the hardware that the acquisition methods of channel mismatching error of time alternative ADC system relates to comprises three parts: the time alternative ADC system 2 of sinusoidal signal generator 1, M passage and the computer 3 of software for mathematical computing MATLAB is housed.The passage label of the time alternative ADC system 2 of M passage is followed successively by 0,1 from top to bottom ..., M-1, clock signal directly provides passage ADC ₀, delay time 1,2 successively then ..., after M-1 sampling period, offer passage ADC respectively ₁, passage ADC ₂..., passage ADC _M-1

The operating frequency of M channel time alternative ADC system 2, promptly the frequency of clock signal is f _s, the sampling period of time alternative ADC system is T _s, T _s=1/f _sProducing frequency with sinusoidal signal generator 2 is f _In=Jf _s/ N＜f _sThe sinusoidal input signal x (t) of/2M, wherein N is single channel sample point number, J and N are relatively prime, satisfy the input signal of the sinusoidal signal x (t) of said frequencies requirement as M channel time alternative ADC system 2, can make sinusoidal input signal x (t) obtain phase place [0,2 π] go up even distribution N different sampled point, help improving computational accuracy.

Sample with time alternative ADC system 2 pairs of inputs sinusoidal signal x (t), each passage is got N=3000 sampled point, with the actual output sequence Y of each passage _i=[y _i[0], y _i[1] ..., y _i[N-1]] i=0,1 ... M-1 deposits in and treats down step processing, wherein y in the computer 3 that software for mathematical computing MATLAB is housed _i[n]=g _iX (nMT _s+ iT _s+ Δ t _i)+os _iChoosing the 0th passage is reference channel, with the actual output sequence Y of 0 passage ₀=[y ₀[0], y ₀[1] ..., y ₀[N-1]] import among the software for mathematical computing MATLAB, with int erp (Y ₀, M) function is to the actual output sequence Y of 0 passage ₀=[y ₀[0], y ₀[1] ..., y ₀[N-1]] do M times of interpolation, obtain the output sequence that there is not channel mismatching error in M channel time alternative ADC system 2 rest channels ${\hat{Y}}_i=\left[{\hat{y}}_i\right[0],{\hat{y}}_i[1],\&CenterDot;\&CenterDot;\&CenterDot;,{\hat{y}}_i[N-1\left]\right],i=\mathrm{1,2}\&CenterDot;\&CenterDot;\&CenterDot;M-1.$

With SIN function Acos (2 π f _Int _n)+Bsin (2 π f _Int _nThe actual output of)+C match rest channels respectively and do not have the output sequence of channel mismatching error, the sinusoidal expression parameter that A wherein, B, C need determine during for match.If

The output sequence that does not have channel mismatching error for passage i

The sinusoidal expression parameter, A _i, B _i, C _iBe the actual output sequence Y of passage i _iThe sinusoidal expression parameter.Sampling model y according to time alternative ADC system _i[n]=g _iX (nMT _s+ iT _s+ Δ t _i)+os _i, can obtain:

$g_i\left\{\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{t}_n\right)\right[{\hat{A}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)+{\hat{B}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{\mathrm{\&Delta;t}}_i\right)]$

$-\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{t}_n\right)[{\hat{A}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)-{\hat{B}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{\mathrm{\&Delta;t}}_i\right)]\}+{\hat{C}}_i+{\mathrm{os}}_i$

$=A_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)+B_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{\mathrm{\&Delta;t}}_i\right)+C_i$

At last, obtaining passage i with respect to the mismatch error of passage 0 is:

$\mathrm{\&Delta;}{t}_i=a\tan \left(\frac{A_i{\hat{B}}_i-{\hat{A}}_i{B}_i}{A_i{\hat{A}}_i+{\hat{B}}_i{B}_i}\right)/2\mathrm{\&pi;}{f}_{\mathrm{in}},$ $g_i=\frac{A_i}{{\hat{A}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;t}\right)+{\hat{B}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;t}\right)},$ ${\mathrm{os}}_i=C_i-{\hat{C}}_i$

Time alternative ADC system 2 offset of sinusoidal input signal x (t) sample, and each passage is got N=3000 sampled point again, repeat above-mentioned steps repeatedly, with the channel mismatching error Δ t that repeatedly obtains _i, g _i, os _iAverage respectively, to reduce the influence of quantization error in the system, random error the channel mismatching error precision obtained.

Fig. 2 is the sampling model of i ADC passage of time alternative ADC system shown in Figure 1

As shown in Figure 2, the sampling model of the single passage of time alternative ADC system, the gain of its i ADC passage, skew and clock delay error are respectively g _i, os _i, Δ t _i, the actual output sequence of i ADC channel sample acquisition is:

y _i[n]＝g _ix(nMT _s+iT _s+Δt _i)+os _i

In this enforcement, the computational accuracy of the channel mismatching error of acquisition relative error formula:

$\frac{\hat{E}-E}{E}\&times;100\%$

Represent, wherein

The channel mismatching error that expression adopts method of the present invention to obtain, E is the physical channel mismatch error.

Fig. 3 is a time alternative ADC system shown in Figure 1 when having quantization error, the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error

In this enforcement, when only there is the 8bit quantization error in time alternative ADC system, the channel mismatching error that calculates of the present invention can be controlled in 4% with respect to the deviation of physical channel mismatch error as seen from Figure 3, and along with increasing of the number of times of the channel mismatching error that repeats to obtain, deviation is further dwindled.

Fig. 4 is a time alternative ADC system shown in Figure 1 when having quantization error and passage random error, the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error

In the present embodiment, there are 8bit quantization error and passage random error in the time alternative ADC system, and it is that 0 variance is when being 0.01 Gaussian Profile that random error is obeyed average, the precision of the channel mismatching error that obtains, as seen from Figure 4, deviation with respect to the actual error channel mismatching error can be controlled in 5%, and along with the increasing of the number of times of the channel mismatching error that repeats to obtain, deviation is further dwindled.

Fig. 5 is that the sinusoidal input signal that sinusoidal signal generator shown in Figure 1 produces comprises harmonic distortion, when time alternative ADC system exists quantization error and passage random error, and the relative error curve chart of channel mismatching error that obtains and physical channel mismatch error

In the present embodiment, there is harmonic distortion among the sinusoidal input signal x (t), existing 8bit quantization error and passage random error to obey average in the time alternative ADC system is that 0 variance is when being 0.01 Gaussian Profile, the precision of the channel mismatching error that obtains, as seen from Figure 5, deviation with respect to the physical channel mismatch error can be controlled in 7%, and along with the increasing of the number of times of the channel mismatching error that repeats to obtain, deviation is further dwindled.

Fig. 6 be the channel mismatching error that obtains according to the present invention to the output waveform figure before and after the high-speed digitization instrument passage output calibration, wherein, Fig. 6 a is the output waveform figure when not calibrating, Fig. 6 b is the output waveform figure after the calibration.

The channel mismatching error of time alternative ADC system that the present invention is obtained is applied in actual 12bit, the calibration of 400MSPs high-speed digitization instrument.This digitizer mainly is made of two channel time alternative ADC systems, because high-speed digitization instrument channel mismatching error is unknown, in order effectively to verify the high accuracy of the channel mismatching error that the present invention obtains, the channel mismatching error that can obtain according to the present invention is exported digitizer and is calibrated, and observes the performance that whether can improve the high-speed digitization instrument.Fig. 6 has shown the channel mismatching error that obtains according to the present invention to the output waveform before and after the high-speed digitization instrument passage output calibration, and before being calibrated as can be seen by Fig. 6 a, because the influence of channel mismatching error, the sinusoidal waveform of output is unsmooth jagged; The channel mismatching error that is obtained according to the present invention as can be seen by Fig. 6 b, after system calibration, the sinusoidal waveform of output is more level and smooth, illustrates that channel mismatching error has reduced, and therefore verifies validity of the present invention.

Although above the illustrative embodiment of the present invention is described; so that the technical staff of present technique neck understands the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various variations appended claim limit and the spirit and scope of the present invention determined in, these variations are conspicuous, all utilize innovation and creation that the present invention conceives all at the row of protection.

Claims (3)

1, a kind of acquisition methods of channel mismatching error of time alternative ADC system is characterized in that, may further comprise the steps:

(1), producing frequency with sinusoidal signal generator is f _InSinusoidal input signal x (t), time alternative ADC system is sampled to this sinusoidal input signal x (t), obtains the actual output sequence Y of each passage _i=[y _i[0], y _i[1] ..., y _i[N-1]] i=0,1 ... M-1, wherein, M is the port number of time alternative ADC system;

(2), to choose certain passage be reference channel, utilizes interpolating function to its actual output sequence interpolation, obtains rest channels does not have mismatch error with respect to reference channel output sequence;

(3), output sequence and actual output sequence that rest channels is not had a mismatch error adopt sinusoidal fitting process to carry out match respectively, constructs the output sequence sinusoidal expression and the actual output sequence sinusoidal expression of no mismatch error of the rest channels of match;

(4), there are not the output sequence sinusoidal expression of mismatch error and the sampling model y of actual output sinusoidal expression and time alternative ADC system according to the rest channels of match _i[n]=g _iX (nMT _s+ iT _s+ Δ t _i)+os _i, obtain the mismatch error of rest channels, wherein g with respect to reference channel _i, Δ t _iAnd c _iThe gain, the sampling clock that are respectively time alternative ADC system i passage postpone and skew T _sBe the sampling period of time alternative ADC system.

2, the acquisition methods of channel mismatching error of time alternative ADC system according to claim 1 is characterized in that, described sinusoidal input signal x (t) frequency is f _In=Jf _s/ N and f _In≤ 1/ (2MT _s), wherein N is single channel sample point number, J and N are relatively prime.

3, the acquisition methods of channel mismatching error of time alternative ADC system according to claim 1 is characterized in that, the SIN function that described sinusoidal fitting process adopts is: Acos (2 π f _Int _n)+Bsin (2 π f _Int _nThe sinusoidal expression parameter that)+C, A wherein, B, C need determine during for match;

The output sequence that does not have mismatch error for passage i

The sinusoidal expression parameter, A _i, B _i, C _iBe the actual output sequence Y of passage i _iThe sinusoidal expression parameter; Sampling model y according to time alternative ADC system _i[n]=g _iX (nMT _s+ iT _s+ Δ t _i)+os _i, obtain:

$g_i\left\{\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{t}_n\right)\right[{\hat{A}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)+{\hat{B}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)]$

$-\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}{t}_n\right)[{\hat{A}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)-{\hat{B}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)]\}+{\hat{C}}_i+o{s}_i$

$=A_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)+B_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;}{t}_i\right)+C_i$

At last, obtaining passage i with respect to the mismatch error of reference channel is:

$\mathrm{\&Delta;}{t}_i=a\tan \left(\frac{A_i{\hat{B}}_i-{\hat{A}}_i{B}_i}{A_i{\hat{A}}_i+{\hat{B}}_i{B}_i}\right)/2\mathrm{\&pi;}{f}_{\mathrm{in},}$ $g_i=\frac{A_i}{{\hat{A}}_i\cos \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;t}\right)+{\hat{B}}_i\sin \left(2\mathrm{\&pi;}{f}_{\mathrm{in}}\mathrm{\&Delta;t}\right)},$ $o{s}_i=C_i-{\hat{C}}_i.$

Images