Demodulation method and circuit for discretely modulated ac signals
US4065722A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 27, 1976 |
| Grant date | Dec 27, 1977 |
| Priority date | — |
| Expiry date | Dec 27, 1996 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/0008
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
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 d…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.