Television – Synchronization – Sync separation
Patent
1996-09-11
2000-11-28
Kostak, Victor R.
Television
Synchronization
Sync separation
348695, H04N 508, H04N 516
Patent
active
061542563
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 lines of video with the frequency of the lines being in a predetermined range and with the last several lines being relatively free of noise. A timer prevents muting of the outputs if the input signal frequency is disturbed only momentarily.
REFERENCES:
patent: 5034815 (1991-07-01), Shibayama
patent: 5274451 (1993-12-01), Koblitz et al.
patent: 5410366 (1995-04-01), Hostetler
patent: 5483289 (1996-01-01), Urade et al.
patent: 5486869 (1996-01-01), Cooper
patent: 5528303 (1996-06-01), Bee et al.
patent: 5619275 (1997-04-01), Tults
patent: 5654764 (1997-08-01), Suh
patent: 5754250 (1998-05-01), Cooper
Gennum Corporation
Kostak Victor R.
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