| 摘要 |
<p>RCA 71,594 A circuit is provided for developing a television synchronization signal and an automatic gain control (AGC) signal. A composite video signal is coupled to the input of a D.C. threshold noise inverter which inverts impulse noise above a predetermined threshold level. The inverted noise signal and a delayed video signal are coupled to a peak detecting sync separator which generates a noise-free sync signal. The noise-free sync signal is coupled to a latching circuit, where it is combined with a horizontal retrace (flyback) signal to produce an AGC keying signal of constant pulse width. An AGC circuit is keyed by the AGC keying signal to generate an AGC control signal from the composite video signal. The time constant of the peak detecting sync separator performs the dual functions of tracking the sync signal of the composite video signal and preventing lockout of the keyed AGC circuit.</p> |
