| 摘要 |
PURPOSE:To easily fix a preset state of a gain adjusting circuit whose gain is kept constant by adding an output from a fixed gain circuit with a control input for gain adjusting, comparing the output of the said addition with a feedback signal, and controlling the gain of a variable gain circuit by means of the output of the said comparison. CONSTITUTION:The synchronization level L of an input video signal from an input terminal 1 is detected by a synchronization-level detector 15, and multiplied G0 by the fixed gain circuit 16, and goes to be G0.L. Since the input video signal is multiplied by G by the variable gain circuit 3, an output of G.L is obtained from a synchronization-level detector 11. Assuming a gain-control input from an input terminal 5 to be (x), the output of an adder 17 will be G0.L+(x), which is transferred to a comparator circuit 12 to be compared with the output of G.L. The gain G of the circuit 3 is controlled so as to make the difference of the said comparison zero. When the preset state is desired, the gain control input (x) is made zero so that the gain G of the circuit 3 comes to be G0, and the level is fixed at the constant preset gain G0 regardless of the synchronization level L.
|
