On FM demodulators in software defined radios using FPGAs

The use FPGAs to implement sampled-data FM demodulators for software-defined radios that must support “legacy waveforms” is explored and analyzed. Feed-forward and feedback structures are examined. The best feed-forward structure, in terms of the time/area trade-off, is the arctangent-differentiator structure. The arctangent-differentiator and PLL demodulators have approximately the same time/area product and approximately the same SNR performance. However, the two occupy very different locations in the time/area trade-off space. Relative to the PLL demodulator, the feed-forward demodulator can achieve a much higher clock rate, but requires more area.