| 摘要 |
PURPOSE: To correct a lower limit gain to be constant at all times by varying a clamp voltage of a control voltage of the automatic gain controller in which a control characteristics of an AGC gain is revised by varying a reference voltage. CONSTITUTION: A variable gain amplifier circuit 1 is controlled by a control voltage Vc whose high frequency component is eliminated. The control voltage Vc is obtained by a voltage resulting from an output voltage of the variable gain amplifier circuit 1 rectified through a rectifier circuit 21 or a voltage detected by a very small voltage detection circuit 8 which is higher and smoothed by a hold circuit 22 via a DC amplifier circuit 3. Since a clamp circuit 7 changes a clamp voltage of the control voltage Vc depending on a reference voltage of a reference voltage circuit 5, even when the AGC characteristics is revised by, changing the reference voltage, the lower limit gain is corrected to be constant at all times. |
