| 摘要 |
PURPOSE:To perform proper AGC operation even at a low source voltage by providing a limiter to the base of an emitter follower transistor (TR) which inputs a control signal to a differential amplifying TR. CONSTITUTION:An input video signal is supplied to the base of one TRQ6 which constitutes a differential amplifier and has a DC voltage source through a TRQ3 and a resistance R6. The base of the other TRQ7 is grounded through R7 and a DC voltage source. The output at a video output terminal 4 is supplied to a detecting circuit 11 through an LPF5 and its detection output is supplied to a limiter circuit 11 and the base of TRQ11. The emitter follower output of the TRQ11 is supplied as a control signal to the variable current source consisting of TRQ 10 and R10. Thus, an input dynamic range is secured and the cutoff phenomenon of the variable current source is eliminated to perform proper AGC operation even at a low source voltage.
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