H - Electricity – 04 – N
Patent
H - Electricity
04
N
H04N 9/44 (2006.01) H04N 5/08 (2006.01) H04N 5/16 (2006.01)
Patent
CA 2157986
Sync separator and video detector circuits, including a sync tip clamp having symmetrical and non-symmetrical clamps. The 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. This is performed by a counter which provides a full count on receipt of the predetermined number of lines, but which has its inputs cleared if the frequency is outside the desired range, and which has its most significant bit cleared if significant noise is present. A timer prevents muting of the outputs if the input signal frequency is disturbed only momentarily.
Bruins Bryan
Moore Paul
Bereskin & Parr
Gennum Corporation
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