Phase locked loop with circuit for preventing sidelock
US4000476A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 7, 1975 |
| Grant date | Dec 28, 1976 |
| Priority date | — |
| Expiry date | Nov 7, 1995 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S331/02
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A side lock detector to prevent side lock in coherent PSK demodulation. For demodulation purposes it is necessary to recreate the carrier at the receiver. This may be accomplished with a phase-locked loop. However, with plural phase PSK modulation the input signal to the phase-locked loop has energy at side bands spaced at modulation rate intervals from the desired lock frequency as well as at the desired lock frequency. To detect side band lock, a band pass filter monitors the phase detector output of the phase-locked loop. The center frequency of the filter is equal to the modulation rate and the filter band width is very narrow. Only during side lock will significant amounts of energy pass the filter. This energy may be detected by a simple diode detector or the like. A lock inhibit means is provided, responsive to the output of the detector, to drive the voltage controlled oscillator out of a side lock condition.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.