Performance of a digital FM demodulator using a fixed‐point arithmetic operation

Abstract

AbstractPerformance 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 40.0 dB to obtain the previously mentioned demodulated SNRs.