| 摘要 |
PURPOSE:To suppress the gain chane of a variable gain amplifier circuit at the scanning of intermediate region by providing a means suppressing the discharge/ charge of a capacitor holding a control voltage. CONSTITUTION:The variable gain amplifier circuit is formed by amplifier 2, 3 and a variable resistive element 5. When a picture signal A from the variable gain amplifier circuit is lower than a level VS as the scanning of the intermediate tone density region, the charging of the capacitor C1 is not performed. Moreover, a switch 8 is turned off by an output of an analog comparator 7, the discharge of the capacitor C1 is suppressed substantially and its discharge time constant is remarkably longer. Thus, the terminal voltage of the capacitor C1, that is, the control voltage is fixed nearly and the gain of the variable gain amplifier circuit is fixed nearly. Thus, the gain change of the variable gain amplifier circuit at the scanning of the intermediate tone region is suppressed. |
