Demodulation method and circuit for discretely modulated ac sign

Details Demodulation method and circuit for discretely modulated ac sign Demodulation method and circuit for discretely modulated ac sign

1976-12-27

1977-12-27

Grimm, Siegfried H.

Demodulators

Amplitude modulation demodulator

Having specific distortion, noise or other interference...

325320, 325338, 325349, 329110, 329126, 329166, H03D 100, H03D 300, H03D 500

Patent

active

040657221

ABSTRACT:
Demodulation of an ac signal that has been modulated by discrete changes in its amplitude, frequency or phase, is effected by first feeding the modulated ac signal through an amplitude limiter and hence through a bandpass filter tuned to a preselected frequency of the ac signal. The resulting bandpass-filtered ac signal defines a variable amplitude envelope which varies in response to amplitude, frequency or phase modulations of the input ac signal. Amplitude variations of the envelope of the bandpass-filtered ac signal are detected by a switching circuit whose operation has been termed "self-synchronous," because it is synchronized to the frequency of the ac signal prior to the passage of the ac signal through the bandpass filter. More particularly, the switching circuit is opened and closed in response to the ac signal appearing at the input to the bandpass filter, to cause alternate, like-polarity half cycles of the bandpass-filtered ac signal to be selectively conducted to a low-pass filter. Filtering by the low-pass filter extracts modulation information from the detected envelope thereby completing the demodulation process. By virtue of the "self-synchronous" detection, the demodulation process is less prone to false detection of modulation information when noise or other spurious signals accompany the modulated ac signal, and is faster in responding to information-bearing changes in the modulated ac signal.

REFERENCES:
patent: 3764926 (1973-10-01), Rypinski, Jr.
patent: 3899741 (1975-08-01), Brandt et al.

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