System and method for distortion analysis

Abstract

A method, circuit and system for determining at least one of an amplitude and a relative phase of a signal under test. A reference signal is generated based, at least in part, upon the at least one of the amplitude and the relative phase of the signal under test. The reference signal is combined with the signal under test to generate a residual signal indicative of a distortion within the signal under test. The residual signal is measured.

1 . A method of analyzing distortion comprising:
 determining at least one of an amplitude and a relative phase of a signal under test;   generating a reference signal based, at least in part, upon the at least one of the amplitude and the relative phase of the signal under test;   combining the reference signal with the signal under test to generate a residual signal indicative of a distortion within the signal under test; and   measuring the residual signal.   
     
     
         2 . The method of  claim 1  wherein the signal under test is an analog signal under test and determining at least one of the amplitude and the relative phase of the signal under test includes:
 providing the analog signal under test to an analog-to-digital converter to generate a digital signal under test. 
 
     
     
         3 . The method of  claim 2  wherein the reference signal is an analog reference signal and generating the reference signal includes:
 receiving the digital signal under test; 
 generating a digital reference signal based, at least in part, upon the digital signal under test; and 
 providing the digital reference signal to a digital-to-analog converter to generate the analog reference signal. 
 
     
     
         4 . The method of  claim 1  wherein the reference signal is essentially out of phase with the signal under test, and wherein combining the reference signal with the signal under test includes:
 adding the reference signal and the signal under test. 
 
     
     
         5 . The method of  claim 1  wherein the reference signal is essentially in phase with the signal under test, and wherein combining the reference signal with the signal under test includes:
 subtracting the reference signal from the signal under test. 
 
     
     
         6 . The method of  claim 1  wherein measuring the residual signal includes:
 providing the residual signal to an analog-to-digital converter. 
 
     
     
         7 . The method of  claim 6  wherein providing the residual signal to an analog-to-digital converter includes:
 amplifying the residual signal. 
 
     
     
         8 . A distortion analysis circuit comprising:
 a sampling circuit configured to determine at least one of an amplitude and a relative phase of a signal under test;   a signal generator circuit configured to provide a reference signal based, at least in part, upon the at least one of the amplitude and the relative phase of the signal under test; and   a combining circuit configured to combine the reference signal with the signal under test to generate a residual signal indicative of a distortion within the signal under test.   
     
     
         9 . The distortion analysis circuit according to  claim 8  wherein the sampling circuit includes an analog-to-digital converter configured to generate a digital signal under test. 
     
     
         10 . The distortion analysis circuit according to  claim 9  wherein the reference signal is an analog reference signal and the signal generator circuit includes a digital-to-analog converter, the signal generator circuit being configured to:
 receive the digital signal under test; 
 generate a digital reference signal based, at least in part, upon the digital signal under test; and 
 provide the digital reference signal to the digital-to-analog converter to generate the analog reference signal. 
 
     
     
         11 . The distortion analysis circuit according to  claim 8  wherein the reference signal is essentially out of phase with the signal under test and the combining circuit is configured to add the signal under test and the reference signal. 
     
     
         12 . The distortion analysis circuit according to  claim 8  wherein the reference signal is essentially in phase with the signal under test and the combining circuit is configured to subtract the reference signal from the signal under test. 
     
     
         13 . The distortion analysis circuit according to  claim 8  further comprising an amplifier circuit configured to amplify the residual signal. 
     
     
         14 . The distortion analysis circuit according to  claim 8  wherein the residual signal is an analog residual signal, the distortion analysis circuit further comprising an analog-to-digital converter configured to process the analog residual signal and generate a digital residual signal. 
     
     
         15 . An automatic test system comprising:
 an input port configured to receive a signal under test from a circuit to be analyzed; and   a distortion analysis circuit including:
 a sampling circuit configured to receive the signal under test and determine at least one of an amplitude and a relative phase of the signal under test; 
 a signal generator circuit configured to provide a reference signal based, at least in part, upon the at least one of the amplitude and the relative phase of the signal under test; and 
 a combining circuit configured to combine the reference signal with the signal under test to generate a residual signal indicative of a distortion within the signal under test. 
   
     
     
         16 . The automatic test system according to  claim 15  wherein the sampling circuit includes an analog-to-digital converter configured to generate a digital signal under test. 
     
     
         17 . The automatic test system according to  claim 16  wherein the reference signal is an analog reference signal and the signal generator circuit includes a digital-to-analog converter, the signal generator circuit being configured to:
 receive the digital signal under test; 
 generate a digital reference signal based, at least in part, upon the digital signal under test; and 
 provide the digital reference signal to the digital-to-analog converter to generate the analog reference signal. 
 
     
     
         18 . The automatic test system according to  claim 15  wherein the reference signal is essentially out of phase with the signal under test and the combining circuit is configured to add the signal under test and the reference signal. 
     
     
         19 . The automatic test system according to  claim 15  wherein the reference signal is essentially in phase with the signal under test and the combining circuit is configured to subtract the reference signal from the signal under test. 
     
     
         20 . The automatic test system according to  claim 15  further comprising an amplifier circuit configured to amplify the residual signal. 
     
     
         21 . The automatic test system according to  claim 15  wherein the residual signal is an analog residual signal, the distortion analysis circuit further comprising an analog-to-digital converter configured to process the analog residual signal and generate a digital residual signal.