CN1941721A - Method for measuring and compensating wide-band orghogonal demodulation unbalance and its measuring equipment - Google Patents

Abstract

The method comprises: 1) building an automatically testing system using measuring apparatus; 2) collecting quadrature demodulation test data in the tested frequency band; 3) processing the collected data to get the amplitude phase unbalance measurement in whole tested frequency band; 4) making classification process for the amplitude phase unbalance in the band measured in step 3; 5) inputting the two kinds of amplitude phase unbalances obtained from step 4 into the amplitude phase unbalance correcting module to correct the error.

Description

Wideband quadrature demodulation disequilibrium survey and compensation method and measuring equipment

Technical field

The present invention relates to communication technical field, particularly a kind of wideband quadrature demodulation disequilibrium survey and compensation method.

Background technology

Often adopt quadrature demodulation that received signal is divided into amplitude in radar and communication and equate, the I/Q two-way of quadrature in phase (90 degree) carries out AD conversion and processing again.Because the undesirable property of device, the amplitude that certainly exists between two-way is inconsistent to depart from 90 problems of spending, promptly so-called imbalance of amplitude and phase problem with phase difference.The existence of imbalance of amplitude and phase will cause parasitic image frequency component in the output signal, and output signal-to-noise ratio is descended.In narrow-band receiver,, can imbalance of amplitude and phase be controlled at small range by meticulous debug circuit because bandwidth is narrower.Along with the increase of receiver bandwidth, the control of imbalance of amplitude and phase is more and more difficult.And along with the increase of bandwidth, the phenomenon of imbalance of amplitude and phase also becomes increasingly complex.In narrow-band receiver, can be similar to and think that imbalance of amplitude and phase is that in broadband receiver, this hypothesis is false not with frequency change.In addition, the power divider in the quadrature demodulation module, frequency mixer, filter all can be introduced imbalance of amplitude and phase, and in output signal, these errors are coupled, and as not distinguished, are difficult to debug targetedly or proofread and correct.

The way of eliminating the quadrature demodulation imbalance of amplitude and phase has two kinds: one, realize IQ width of cloth phase quadrature by debugging orthogonal demodulation circuit meticulously, in broadband receiver, this way is unrealistic; Two, obtain the imbalance of amplitude and phase error of orthogonal demodulation circuit by test, utilize signal processing that imbalance of amplitude and phase is compensated.This method has flexibly, characteristic of accurate, is suitable for the unbalanced correction of wideband quadrature demodulation.

At present, the uneven method of testing of two class quadrature demodulations is arranged.One class is directly to utilize the echo-signal of receiver, extracts the imbalance of amplitude and phase parameter, and the advantage of this method is not need extra corollary equipment, can measure the error of quadrature demodulation module at any time; Because what adopt is the method for statistics, shortcoming is that error is bigger, and can only measure not with the imbalance of amplitude and phase of frequency change, is unsuitable for broadband system.The method that an other class is based on apparatus measures can accurately be measured the imbalance of amplitude and phase with frequency change, but shortcoming is a very flexible, can only be in laboratory measurement, and also along with the increase of test frequency, test job efficient is low.More than two class methods to have a common shortcoming be can not distinguish because the imbalance of amplitude and phase that frequency mixer and filter cause can't provide foundation for accurately proofreading and correct targetedly.

Summary of the invention

Measurement and correction problem at the imbalance of amplitude and phase of wideband quadrature demodulation module, the thinking that addresses this problem both at home and abroad is by instrumentation imbalance of amplitude and phase to be measured, eliminate this error by adjusting circuit then, or eliminate error by the means of signal processing.Our thinking is to adopt means automatic unbalance response of measuring module to be measured in whole test frequency range of test automatically, and is wideer in the test bandwidth, when test frequency density is big, can increase work efficiency greatly; In addition, we have found the influence difference of the unbalance response of separate sources in the quadrature demodulation module to system by analysis, the method of proofreading and correct also needs to distinguish to some extent, so we have adopted the imbalance of amplitude and phase sorting technique that the imbalance of amplitude and phase of separate sources is classified in the processing to test data.In imbalance of amplitude and phase is proofreaied and correct, we considered the imbalance of amplitude and phase at separate sources carry out different, proofread and correct targetedly.Relative conventional method, the method efficient that we propose is higher, more accurate.

Description of drawings

Fig. 1 is the Automatic Test Equipment connection layout.

Fig. 2 is the circuit diagram of quadrature demodulator.

Fig. 3 is the IQ of a system error correction schematic diagram.

Fig. 4 is a LO phase error correction schematic diagram.

Fig. 5 formula wideband quadrature demodulation disequilibrium survey of the present invention and compensation method flow chart.

Embodiment

We have proposed a kind of accurately measuring and bearing calibration with the frequency change imbalance of amplitude and phase based on apparatus measures.This method can effectively be distinguished the imbalance of amplitude and phase that different error sources are introduced; This method adopts automatic means of testing, has improved testing efficiency greatly; This method can realize that imbalance of amplitude and phase is proofreaied and correct targetedly, has improved correction accuracy.

Testing equipment comprises: signal source, digital oscilloscope, control computer, GPIB cable etc.; To be measured is quadrature demodulation module or receiver.Instrument connects as Fig. 1.The control computer produces needed test signal by GPIB cable control signal source; Test signal is input to the input of quadrature demodulation module, and demodulated I/Q output is input to two input channels of digital oscilloscope respectively.After digital oscilloscope is gathered i/q signal, give the control computer by the GPIB cable and handle.

Measure for wideband quadrature demodulation, send control command, allow signal source in measuring frequency band, produce the test signal of respective frequencies, gather demodulation result by control computer control digital oscilloscope then by the control computer.Above process does not need the people to participate in by program control, can increase work efficiency greatly.

For quadrature demodulator as shown in Figure 2, if input signal is:

x(t)＝Acos2πf _ct

Local oscillator LO signal is:

x(t)＝A _LOcos2πf _LOt

After the 90 degree phase shifts, owing to there is the phase shift error, output signal is:

x(t)＝A _LOsin(2πf _LOt+θ)

Because two interior low pass filter and other devices of passage also can be introduced amplitude-frequency and phase frequency imbalance, suppose at test frequency f _c, the amplitude-frequency of its introducing and phase frequency imbalance are A _e, and  _eThen exist the I/Q of the Orthodox Church demodulate reception machine of error to be output as:

I(t)＝A _ocos[2π(f _LO-f _c)t]

Q(t)＝A _oA _esin[2π(f _LO-f _c)t++θ]

The method of testing that utilization is introduced above can be gathered the i/q signal of receiver output.The frequency f of test signal _CnShould cover the working band of quadrature demodulator.Therefore, can obtain one group of test result.I channel signal and Q channel signal are carried out Hilbert transform and Fourier transform respectively can obtain following signal:

The amplitude of two paths of signals output peak value and the amplitude imbalance A that phase place can obtain at this test frequency after the comparison process _eWith unbalance in phase +θ.All test frequencies in the working band are repeated above the processing, both can obtain amplitude and unbalance in phase curve with frequency change.

Fig. 3 is the IQ of a system error correction signal process

Obtained the imbalance of amplitude and phase of system by top processing, but imbalance of amplitude and phase for the fine compensation system, unbalance in phase particularly, also need to distinguish because the unbalance in phase θ that the local oscillator phase shifter is introduced, and, compensate respectively then owing to inconsistent unbalance in phase  that causes such as low pass filters.Suppose the unbalance in phase of α for obtaining by test.The character of  and θ more then, can utilize following formula to calculate:

$\mathrm{\θ}(f_{\mathrm{LO}}+\mathrm{\Δf})=-\mathrm{\θ}(f_{\mathrm{LO}}-\mathrm{\Δf})=\frac{\mathrm{\α}(f_{\mathrm{LO}}+\mathrm{\Δf})-\mathrm{\α}(f_{\mathrm{LO}}-\mathrm{\Δf})}{2}$

Signal after the mode that can adopt Digital Signal Processing under the prerequisite that obtains IQ error measure curve and corresponding error pattern is to the AD sampling carries out the correction of quadrature demodulation imbalance of amplitude and phase.If if the phase error that known local oscillator LO causes is θ, because IQ passage low pass filter and inconsistent phase error and the range error with frequency change that causes of other passages are respectively  (f) and A _e(f), then the imbalance of amplitude and phase compensation scheme of IQ passage is as shown in Figure 3:

Fig. 4 is a LO phase error correction signal process

At first, proofread and correct in the following way for the LO phase error theta,

$x_{\mathrm{qc}}\left(t\right)=\frac{x_q\left(t\right)}{\cos \left(\mathrm{\θ}\right)}-x_i\left(t\right)\tan \left(\mathrm{\θ}\right)\·\·\·1$

Signal after the correction LO phase error is carried out the FFT computing, then at quadrature demodulation unbalance in phase  (f) and the amplitude imbalance A of frequency-domain correction with frequency change _e(f);

$X_{\mathrm{QC}}=F\left[x_{\mathrm{qc}}\left(t\right)\right]\·\·\·2$

Can obtain not have the IQ signal x of IQ error after the correction _I(t) and x _Q(t).

Wideband quadrature demodulation disequilibrium survey and the compensation method of Fig. 5, its concrete steps are as follows:

Step S1 utilizes signal source, data acquisition equipment, control computer, control cable etc. to make up quadrature demodulation imbalance of amplitude and phase Auto-Test System, and the control computer is coordinated each tester and finished collection to the test data of quadrature demodulation module;

A, at first utilize high frequency cable to connect tester and module to be measured, the output of local oscillator simulation signal generator connects the local oscillator input of quadrature demodulation module to be measured, high-frequency signal source output connects the signal input of module to be measured, and the I/Q output of module to be measured connects double channel data acquisition equipment;

B, secondly utilizes control cable to connect control computer, high-frequency signal source and double channel data acquisition equipment;

C, the control computer by control cable control high-frequency signal source in test frequency range to the test frequency point scanning, and control data collecting device synchronous acquisition and store the IQ demodulation dateout of quadrature demodulation module simultaneously;

Step S2, the data that step S1 gathers are handled, at first, by signal is carried out the Hilbert conversion, carry out the Fourier conversion then, at the test frequency transformation results of two passages is compared, can obtain the amplitude and the unbalance in phase measured value of this frequency, all test frequencies in the test frequency range are repeated the imbalance of amplitude and phase that above step can obtain in the whole test frequency range measure;

Step S3, imbalance of amplitude and phase processings of classifying in the band that step S2 is measured is zero point with the centre frequency of test frequency range, in the imbalance of amplitude and phase with this at zero point symmetry part be error owing to the low pass filter introducing; In the imbalance of amplitude and phase with zero point antisymmetric part be because the error that local oscillator phase shifter and frequency mixer are introduced;

Step S4, the two class imbalance of amplitude and phase that S3 is obtained are input in the imbalance of amplitude and phase correction module, this module is the software that is embedded in the IQ data acquisition equipment, it is input as IQ binary channels data, this module at first concerns by trigonometric function, realization replenishes the error introduced by local oscillator phase shifter and frequency mixer, then data is carried out the Fourier conversion, realizes because the correction of the error that low pass filter is introduced at frequency domain.

The elite point:

1,, can distinguish the measurement scheme and the post-processing approach of the IQ imbalance of amplitude and phase of frequency mixer and filter error based on apparatus measures;

2, can proofread and correct the less digit correction method of the IQ imbalance of amplitude and phase of frequency mixer and filter introducing respectively.

Claims (2)

1. wideband quadrature demodulation disequilibrium survey and compensation method, signal source, data acquisition equipment instrument built becomes the quadrature imbalance automatic measuring system, finish collection to the quadrature unbalanced data, utilize Digital Signal Processing to finish amplitude and the unbalance in phase characteristic that the analysis of the data of gathering is obtained device under test, then the result that will measure is input in the quadrature demodulation imbalance of amplitude and phase correction module, realize undistorted quadrature demodulation, its concrete steps are as follows:

Step S1 utilizes signal source, data acquisition equipment, control computer, control cable etc. to make up quadrature demodulation imbalance of amplitude and phase Auto-Test System, and the control computer is coordinated each tester and finished collection to the test data of quadrature demodulation module;

A, at first utilize high frequency cable to connect tester and module to be measured, the output of local oscillator simulation signal generator connects the local oscillator input of quadrature demodulation module to be measured, high-frequency signal source output connects the signal input of module to be measured, and the I/Q output of module to be measured connects double channel data acquisition equipment;

B, secondly utilizes control cable to connect control computer, high-frequency signal source and double channel data acquisition equipment;

C, control computer by control cable control high-frequency signal source in test frequency range to the test frequency point scanning, and control data collecting device synchronous acquisition and store the IQ demodulation dateout of quadrature demodulation module simultaneously;

Step S2, the data that step S1 gathers are handled, at first, by signal is carried out the Hilbert conversion, carry out the Fourier conversion then, at the test frequency transformation results of two passages is compared, can obtain the amplitude and the unbalance in phase measured value of this frequency, all test frequencies in the test frequency range are repeated the imbalance of amplitude and phase that above step can obtain in the whole test frequency range measure;

Step S3, imbalance of amplitude and phase processings of classifying in the band that step S2 is measured is zero point with the centre frequency of test frequency range, in the imbalance of amplitude and phase with this at zero point symmetry part be error owing to the low pass filter introducing; In the imbalance of amplitude and phase with zero point antisymmetric part be because the error that local oscillator phase shifter and frequency mixer are introduced;

Step S4, the two class imbalance of amplitude and phase that S3 is obtained are input in the imbalance of amplitude and phase correction module, this module is the software that is embedded in the IQ data acquisition equipment, it is input as IQ binary channels data, this module at first concerns by trigonometric function, realization replenishes the error introduced by local oscillator phase shifter and frequency mixer, then data is carried out the Fourier conversion, realizes because the correction of the error that low pass filter is introduced at frequency domain.

2. a wideband quadrature demodulation disequilibrium survey equipment comprises: signal source, digital oscilloscope, control computer, GPIB cable; To be measured is quadrature demodulation module or receiver, and the control computer produces needed test signal by GPIB cable control signal source; Test signal is input to the input of quadrature demodulation module, and demodulated I/Q output is input to two input channels of digital oscilloscope respectively, after digital oscilloscope is gathered i/q signal, gives the control computer by the GPIB cable and handles.

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