| 摘要 |
PURPOSE:To obtain a wide gain range and a stable circuit by using an output voltage of a comparison amplifier as a reference potential for a clamp potential and applying it to a double balancing differential amplifier as the reference potential to apply differential operation to the video input. CONSTITUTION:An output terminal 30 of the comparison amplifier 10 is branched and connected to a variable gain circuit 3 as a terminal for a reference potential. That is, an output voltage O2 of the comparison amplifier 10, that is, the clamp potential is applied as the reference potential Vref4 inputed to a reference potential input terminal 31. Thus, when the voltage of the gain control terminal 4 is lower than the set voltage Vref3 corresponding thereto by a degree or more, that is, when the gain is close to zero, a current proportional to the clamp potential, i.e., the output voltage O2 of the comparison amplifier 10 flows to a load resistor 25, and a voltage amplified by a gain A1 decided by resistors 22, 25, 27, 28 is generated to an output terminal 29. That is, even with the gain of the variable gain circuit 3, the fluctuation of the clamp potential is given to the output terminal 29 with a constant gain at all times and the pedestal potential of the output terminal 29 is kept to a constant value.
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