| 摘要 |
PURPOSE:To improve the transient characteristics without lowering the demodulating distortion of low frequency, by providing a means that gives a conduction to a switch circuit in case when the voltage of the demodulation output terminal is higher than the voltage of the gain control input terminal by a prescribed value. CONSTITUTION:The difference of potential between terminals A and B becomes instantaneously to >=(2XVBE) when the receiving state is changed to the tuning from the detuning. As a result, the transistor 15 conducts and accordingly the resistance 16 becomes dominant to the T type impedance circuit consisting of the resistances 1 and 2 plus capacitor 3 and in the form of an AC impedance between the terminals A and B. Then the low-pass filter connected between the terminals A and B selects a proper value for the resistance 16. As a result, the AGC circuit approximates to the primary answer to eliminate the malformation of a station detector (detecting circuit for presence or absence of receiving station) which is caused by the transient answer of the AGC circuit. The transistor 15 does not conduct in the tuning state. |
