Digital pulse frequency demodulation using state-space filtering

Independently of the method of demodulation, the time quantisation of a pulse frequency modulated signal causes an error proportional to the demodulator bandwidth, to the time quantisation interval, and to the ratio of the modulation frequency to the modulation frequency range. The necessity of having a very short quantisation interval leads to a very high effective input sampling rate to a digital demodulator. This high effective sampling rate, together with large time constants needed to demodulate the signal, precludes the use of a conventional digital filter. It is possible, however, to take advantage of the special form of the demodulator input signal to design a computationally efficient state-space filter.