A DIGITAL FM DEMODULATOR FOR FM, TV, AND WIRELESS

An FM demodulator is implemented digitally in software using a quadri- correlator algorithm so that the FM function can be made compatible wi th future digital wireless and FM receiver systems. The proposed digit al FM demodulator uses a sinc(3) decimation filter with its first zero either on the alternate channels or on the adjacent channels for high channel selectivity, a digital differentiator using a three-point app roximation for frequency discrimination, and a digital division for AM rejection. A bitstream FM signal from a fourth-order bandpass delta-s igma modulator is FM-demodulated to exhibit a SNDR of 71 dB, a THD of 0.01%, and an AM rejection of 77 dB in simulations using a signal band limited to 1/200 of the sampling frequency and amplitude-modulated wit h a modulation index of 0.9 (90% AM).