Pulse or digital communications – Equalizers – Automatic
Patent
1997-07-03
2000-03-28
Chin, Stephen
Pulse or digital communications
Equalizers
Automatic
375284, H03H 730, H03H 740, H03K 5159
Patent
active
060441127
ABSTRACT:
Methods and apparatus for detecting and correcting phase and amplitude imbalances existing between I (in-phase) and Q (quadrature phase) signal components of a complex signal, e.g., QAM or OPSK signal, that is being demodulated are described. The phase and amplitude imbalance and correction circuitry of the present invention are implemented as decision directed control loops which can be used in conjunction with an overall decision directed gain control loop. Amplitude imbalance is corrected by adjusting the gain of one of the I and Q signal components. Phase imbalance is corrected by adding a portion of one of the I and Q signal components to the other one of the I and Q signal components. Overall amplitude control is achieved by adjusting the gain of both the I and Q signal components by the same amount. Various embodiments of the present invention utilize I/Q differential amplification and cross coupling to compensate for amplitude or phase imbalance with amplitude and phase correction factors being calculated in an automatic closed loop fashion by examining sliced errors and the location of their corresponding target symbols. The present invention is well suited for use, in, e.g., QPSK and/or QAM demodulators.
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Chin Stephen
Hitachi America Ltd.
Phu Phuong
Straub Michael P.
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