A Phase Tracking Loop (PTL) Detector for FM Signals and Its Application to CD-4 System
A new FM demodulation technique has been developed introducing an idea of feedback controlled variable center-frequency filter. The circuit consists of a variable frequency band pass filter, a Hilbert filter, a phase comparator, a loop filter, and a loop amplifier. It features a wide dynamic range; a high S/N ratio; and a less spurious response. This is an excellent high fidelity FM detector for the CD-4 disc system in particular.
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