Digital FM Discriminator System

Abstract

The Digital FM Discriminator described in this paper is used to demodulate FM signals with a high percentage (±40%) deviations. When contrasted to the conventional constant pulse width or the phase locked loop discriminators, the digital system has advantages of improved linearity and distortion performance. Additionally, because of the digital nature of the circuit, it requires no adjustment during setup or manufacture. The digital discriminator can be operated at any center frequency within the range of the integrated circuits used, provided that the proper ratio of the FM carrier center frequency and the clock frequency of the discriminator is maintained. In other words, the center frequency of the discriminator can be altered by altering the clock frequency. The digital discriminator provides an analog output which is a step-by-step reconstruction of the original modulating signal. In addition a digital word for each cycle of the FM carrier is generated corresponding to the amplitude of the modulating signal at that instant. The digital output is available in parallel as well as serial format.