Circuit for demodulating a frequency-modulated signal

Details Circuit for demodulating a frequency-modulated signal Circuit for demodulating a frequency-modulated signal

1987-05-28

1988-10-11

Grimm, Siegfried H.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

329126, H03D 304, H03D 320, H03K 906

Patent

active

047774509

ABSTRACT:
A demodulating circuit includes an exclusive OR gate which has a first input for a frequency modulated signal and a second input connected via a delay to a frequency dividing circuit. The second input is initially low so that an output signal is produced by the gate, enabling a pulse generator, whenever the first input is high. The pulse generator produces a train of pulses of predetermined length and frequency. These pulses are counted in a counter and the count is compared in a comparator with a predetermined number n. On the n.sup.th pulse, the comparator sets a bistable circuit which then produces an end-of-pulse-train signal, triggering the frequency dividing circuit. In response, the frequency dividing circuit produces an output signal which causes the second input of the OR gate to go high, thereby disabling the pulse generator. The pulse generator is then re-enabled when the first input of the gate goes low, thereby indicating a zero-cross-over point, in the negative-going direction, of the frequency-modulated signal. The demodulated signal is produced by filtering and integrating successive pulse trains produced by the pulse generator.

REFERENCES:
patent: 2956227 (1960-11-01), Pierson
patent: 3638128 (1972-01-01), Downs
patent: 4091330 (1978-05-01), Hidaka
patent: 4350957 (1982-09-01), Miyamoto

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