| 摘要 |
PURPOSE:To obtain excellent AGC characteristics by inputting an input signal to an attenuator after being amplified by an amplifier and inputting a digital signal to the attenuator to control the attenuation of the attenuator. CONSTITUTION:The signal power value of the input signal applied to a signal input terminal 17 is calculated by a rectifier circuit 14, an integration circuit 15 and a decibel converting circuit 16, its signal power and a signal to a setting power input 38 are added by an adder 37, and the result is converted into n-bit digital signals 19-22 by an A/D converter 13. On the other hand, the input signal is amplified by a prescribed gain's share by a negative feedback amplifier consisting of an operational amplifier 1 and resistors 7, 8 and the result enters the input of the attenuator 23. The attenuation is adjusted for the signal entering the attenuator 23 by an output signal of n bits from the A/D converter 13. Since the circuit is so constituted that the signal entering the signal input terminal 17 is attenuated while amplified once, even if the input is a signal having a low signal power, the S/N is not deteriorated, and since the attenuator 23 is placed behind the operational amplifier 1, the effect of the input impedance of the operational amplifier 1 is avoided in AGC characteristic. |
