| 摘要 |
PURPOSE:To obtain a stable output even with a video signal in the vicinity of a black level, by providing a buffer amplifier amplifying the potential of the connecting point of the 1st and the 2nd amplifiers and feeding back it to the 1st amplifier for decreasing an output impedance of the 1st amplifier. CONSTITUTION:A base circuit of an input transistor (TR) Q1 is provided with a buffer amplifier comprising TRs Q3, Q4, resistors R1, R2, R3 and a current source I2. Further, the TRQ1 is controlled for the conduction with a potential at a connecting point B between the resistor R3 and the TRQ4, and the conduction of the TRQ4 is controlled with a potential at a connecting point C between the TRQ1 and the current source I1. The connecting point B and a power supply VCC is connected with the TRQ5 and the conduction is set with a bias source V1, the connecting point C and the power supply VCC is connected with a TRQ2, and the conduction is set with a potential V1 in common with the TRQ5 and an output signal is obtained from the connecting point C. Thus, the output impedance of the TRQ1 is set smaller in comparison with an AC resistor of the TRQ2 side, allowing to make the change in the slow conductiv resistance of the TRQ1, T2 steep. |
