Decoder circuit for phase modulated signals

摘要

A decoder circuit (21) and method for providing an amplitude compensated signal by removing the undesired effect of amplitude modulation on a phase modulated signal. The decoder method is provided by demodulating a received inphase receive signal component (10) and quadrature receive signal component (12) of the phase modulated signal and outputting an amplitude varying signal (15) to a feedforward automatic gain control circuit that outputs an amplitude compensated signal (38). The feedforward automatic gain control circuit comprises a detector circuit (16), an offset bias circuit (32), a differencer circuit (30) and a gain control circuit (28). The detector circuit (16) outputs a DC signal (17) representing an amplitude of the inphase receive signal (10) and the quadrature receive signal (12). The offset bias circuit (32) provides a constant current bias (29) to the DC signal (17) thus creating a control signal 31. The gain control circuit (28) receives the control signal (31) and the amplitude varying signal (15) and outputs an amplitude compensated signal (38).