| 摘要 |
An AGC gate signal generating circuit for a television receiver comprises a series RC circuit having a time constant for developing a charging current at a relatively slow rate in relation to a horizontal scanning line of a video signal and at a relatively fast rate in relation to a field of the video signal. The AGC gate signal is developed at the collector of a transistor whose base is coupled for receiving the video signal and whose emitter is coupled to the node formed between the resistor and capacitor of the RC circuit. The transistor is responsive to a nomimal level video signal for assuming a non-conductive state during horizontal scanning lines for charging the capacitor to a level below the video black level and for assuming a conductive state during horizontal sync intervals for discharging the capacitor to produce the collector current AGC gate signal. The transistor further assumes a conductive state for producing the AGC gate signal in response to a number of horizontal scanning lines of a reduced level video signal substantially less than a full field.
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