Discrete-time quadrature FM detection

A digital version of a tried and true analog narrowband frequency modulation (FM) demodulation technique is introduced. The digital demodulator is implemented with a second-order IIR filter and a computationally efficient Hilbert transformer. An expression is given, enabling the design of a simple three-tap, linear-phase narrowband FIR clean-up filter requiring only two additions and one multiply filter output sample.