Demodulators – Phase shift keying or quadrature amplitude demodulator
Patent
1996-09-13
1998-01-06
Mis, David
Demodulators
Phase shift keying or quadrature amplitude demodulator
329318, 329341, 375349, H03D 300
Patent
active
057059497
ABSTRACT:
A method in which correctable I/Q imbalance errors in a complex receiver can be detected and compensated for digitally without the use of special calibration signals. Differential D.C. offset errors are compensated by averaging the incoming I.sub.d and Q.sub.d digital signals and subtracting from them an expected value of differential D.C. offset, for example, computed from the long term average of the I and Q signals to create I' and Q' signals. Differential gain imbalance errors are corrected by calculating a root means square average of the I' and Q' digital signals and applies to them compensation coefficients K.sub.x and K.sub.y determined from either the RMS average or from a Stochastic Gradient Algorithm. The DSP compensates for the quadrature phase errors by calculating a compensation matrix which is independent of the frequency of the carrier and applies the compensation matrix to the I' and Q' digital signals. The compensation matrix for quadrature phase errors is completely independent of the frequency of the input carrier signal supplied to the complex receiver, and is not dependent on the use of a calibration signal. The compensation may be performed as a step in calibration of the complex receiver, or continuously.
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Alelyunas Carl H.
Norrell Andrew L.
Parizhsky Vladimir
Mis David
U.S. Robotics Access Corp.
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