A method of demodulating an FM signal with a hybrid phase-locked loop is presented. In contrast to conventional phase-locked loops, the circuitry is for the most part digital, rather than analog. Advantages, such as stability and absence of adjustments, make a digital or hybrid phase-locked loop more suitable for use in large systems which require microminiaturization. 

A function generator integrated circuit supplies a frequency modulated signal to the phase detector, which consists of a double balanced mixer and a low pass filter. This low pass filter serves to eliminate the high frequency components of this signal. A software program then performs an A/D conversion which translates an analog signal into a series of 8-bit binary data. The superimposed AC components are then filtered out by a software representation of a digital filter. In addition, software programming is then used to implement a digital synthesizer, operating at a fixed clock rate to sample the synchronized signal at different sampling instants. 
 

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