| 摘要 |
PURPOSE:To increase the S/N through the reduction of high band cut-off frequency at a weak electric field, by changing the time constant of a capacitor for time constant circuit connected to an output terminal through the output impedance of a detected output changed according to the strength of received electric field. CONSTITUTION:After an intermediate frequency signal from a front end applied to an input terminal 1N is amplified at an intermediate frequency amplifier 11, the signal is detected at a detection circuit 12. After the circuit 12, a variable output impedance circuit 13 is inserted, which is controlled with an output of a level detector 14 detecting the output level of the amplifier 11. The time constant of a time constant circuit 15 consisting of a variable output impedance circuit and a capacitor C connected to an output terminal OUT is changed according to the strength of received electric field. |
