The present invention is related to methods and apparatus that compensate
for quadrature impairments of an analog quadrature modulator and/or
demodulator over a relatively wide signal bandwidth. One embodiment
pre-distorts baseband signals in a quadrature modulator compensation
signal processor (QMCSP) to negate the quadrature impairment of an analog
quadrature modulator and corrects a received baseband signal in a
quadrature demodulator compensation signal processor (QDCSP) to cancel
the quadrature impairment of an analog quadrature demodulator. The QMCSP
and the QDCSP contain adaptive digital filter correction structures that
pre-compensate and post-compensate, respectively, for the quadrature
impairments introduced by the analog quadrature modulator and the analog
quadrature demodulator over a relatively wide bandwidth. A phase shifter
advantageously shifts the phase of a local oscillator signal to the
analog quadrature demodulator to distinguish quadrature impairments
introduced by the modulation path from quadrature impairments introduced
by the demodulation path.