Sync separator and video signal detector circuits
US6154256A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 11, 1996 |
| Grant date | Nov 28, 2000 |
| Priority date | — |
| Expiry date | Sep 11, 2016 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N5/08
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A symmetrical clamp clamps the input video signal to a reference voltage during composite sync pulses, so the coupling capacitor discharge current is kept small between composite sync pulses. For startup, the non-symmetrical clamp employs an operational amplifier, diode and controllable current source to charge the coupling capacitor to a minimum desired level, and to discharge the capacitor e.g. when there is a change in DC level so that the output level is too high. A sync slicing detector is also provided, using two comparators. One comparator compares the slicing level with the clamped video and produces a properly sliced composite sync output, while the other compares the clamped video with a small reference voltage and produces a fixed sync output. If the clamped video level drops suddenly, a delayed version of the fixed composite sync output clocks a flip flop, creating a fault signal which discharges a memory capacitor over a time period. When composite sync pulses are again sliced, the output from the first comparator resets the flip flop. The circuit also includes a video signal detector which enables its sync outputs only when it receives a predetermined number of valid …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.