| 摘要 |
PURPOSE:To prevent beat disturbance, etc., by holding the total gain of a PLL circuit constant by using a variable gain controlling circuit. CONSTITUTION:The output signal of IF amplifying circuit 5 is supplied to phase comparator 8a constituting PLL circuit 8 via variable gain controlling circuit 11. The output signal of voltage-controlled oscillator 8c is supplied to comparator 8a and also to multiplying circuit 6 via 90 deg. phase shifting circuit 9. A detection signal appearing at the output side of this circuit 6 is supplied to voice signal output terminal 10 and also supplied to level detecting circuit 13. The output signal of this circuit 13 is supplied as a gain signal to high-frequency amplifying circuit 2 and circuit 5 to control their gains, and the output signal of this circuit 13 is supplied as a gain control signal to circuit 11 via DC amplifying circuit 14 to control the gain of circuit 11 according to the input signal level. Consequently, circuit 8 can operate stably and the generation of a higher harmonic signal can be suppressed low, so that beat disturbance, etc., are prevented. |
