Performance of a Digital FM Demodulator Using a Fixed-Point Arithmetic Operation.

Performance of a DSP demodulator for FM broadcasting receiver is examined by computer simulation and system parameters suitable for obtaining demodulated signal quality (SNR) are clarified. The DSP demodulator is preceded by an m-digit linear A-D converter operating at the IF stage of the receiver. A relation between required values of n, the register length of the processor, and m is investigated under the condition that a demodulated signal SNR of 60 dB and 55 dB for monophonic and stereophonic signals, respectively, is ensured. Moreover, only a slight increment of C/Ni (C is input carrier power; Ni is thermal noise power at the receiver input) is necessary to recover degradation due to quantization noise and mathematical rounding-off errors. Simulation results show that demodulation can be performed with a margin by using parameters n = 16 with m = 7 and 10 under the condition of C/Ni = 23.5 dB and 40.5 dB for monophonic and stereophonic signals, respectively. However, an ideal analog receiver requires C/Ni of 23.2 and 0,0.0 dB to obtain the previously mentioned demodulated SNRs. [ABSTRACT FROM AUTHOR]