An FM demodulator is implemented digitally in software using a quadri-correlator algorithm so that the FM function can be made compatible with future digital wireless and FM receiver systems. The proposed digital FM demodulator uses a sinc/sup 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 approximation for frequency discrimination, and a digital division for AM rejection. A bitstream FM signal from a fourth-order bandpass delta-sigma modulator is FM-demodulated to exhibit a SNDR of 71 dB, a THD of 0.010%, and an AM rejection of 77 dB in simulations using a signal bandlimited to /sup 1///sub 200/ of the sampling frequency and amplitude-modulated with a modulation index of 0.9 (90% AM).
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