| 摘要 |
PURPOSE:To decrease number of external terminals of an IC and also number of externally mounted components by using a voltage generated at a low cut circuit as an AGC signal to control the gain of an intermediate frequency amplifier. CONSTITUTION:A connecting point between a resistor R4 and an inverting input terminal is connected to an external terminal 31 and connected to an external terminal 32 and an intermediate frequency amplifier 4 via a resistor R5. A capacitor C4 is connected between the external terminal 31 and ground and a capacitor C5 is connected between the external terminal 32 and ground. Further, a signal at a connecting point A between the resistor R4 and an inverting input of a differential amplifier 30 receives a low pass characteristic by the resistor R4 and the capacitor C4, the signal at the point A is smoothed by the resistor R6 and the capacitor C5 and the result is fed to the intermediate frequency amplifier 4 and the gain of the amplifier 4 is controlled. The output of an AM demodulation circuit 5 is subject to low cut-off characteristic by only the connection of the capacitors C4, C5 to the external terminals 31, 32 and AGC is applied to the amplifier 4.
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