| 摘要 |
PURPOSE:To improve the suppressing ratio of a control signal of a gain control circuit, by providing a bias circuit controlling a DC potential of a video signal with the DC potential of a video signal at the blanking period and an output signal of a comparison circuit detecting the error with a reference potential, for compensating the bias potential error due to the element variance. CONSTITUTION:Differential transistors (TRs) Q15, Q16 are operated only at the blanking period, compare a potential of blanking period of a signal given to a base of the TRQ16 with a bias potential V4 given to the base of the Q15, the error voltage is current-amplified. The result is converted into a voltage at a resistor R16 via a current mirror consisting of a TRQ18, a diode D1, and resistors R14, R15, the peak detection is done at a detecting circuit comprising a TRQ19, a resistor R17 and a capacitor C4 and the result is converted into a DC voltage, the collector current of a TRQ26 is controlled, the DC current component of the collector current of the current mirror Q26 is cancelled so as to form a current flowing to a load resistor R18 only with a signal current component. Thus, the bias voltage of TRs Q9, Q10 is given from a bias power supply V4 via the resistors R18, R19 respectively at all times, and the leakage of the control signal produced with the base potential error is prevented. |
