Hybrid Phase-Locked Loop for FM Demodulation
Mike Casina and Sarboland Sadiq
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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