An FM demodulator is implemented digitally in software using anquadri-correlator algorithm so that the FM function can be madencompatible with future digital wireless and FM receiver systems. Thenproposed digital FM demodulator uses a sinc3 decimationnfilter with its first zero either on the alternate channels or on thenadjacent channels for high channel selectivity, a digital differentiatornusing a three-point approximation for frequency discrimination, and andigital division for AM rejection. A bitstream FM signal from anfourth-order bandpass delta-sigma modulator is FM-demodulated to exhibitna SNDR of 71 dB, a THD of 0.010%, and an AM rejection of 77 dB innsimulations using a signal bandlimited to 1/200 ofnthe sampling frequency and amplitude-modulated with a modulation indexnof 0.9 (90% AM)
展开▼
