Automatic frequency control
US4814887A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 23, 1988 |
| Grant date | Mar 21, 1989 |
| Priority date | — |
| Expiry date | May 23, 2008 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03J7/04
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An automatic frequency control tracks a television signal before and after a period of interruption. The automatic frequency control comprises a voltage controlled feedback loop including a voltage controlled local oscillator and a mixer for mixing the output of the oscillator with the TV signal. The output of the mixer is filtered to remove unwanted components of the mixed signal and to equalize sidebands of the television signal. The output of the filter is supplied to a detector which is tuned to a component of the television signal, and produces a voltage corresponding to the frequency of the component. The output of the detector is supplied to the voltage control input of the local oscillator to track the television signal component. Circuitry automatically senses the absence of the TV signal component from the mixer, and automatically applies a reference voltage to the voltage control input of the oscillator when the TV signal component is absent. The detector is operative to detect the television signal component following the application of reference voltage to the oscillator so that when the television signal returns, the detector is capable of tracking it.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.