| 摘要 |
PURPOSE:To prevent the deterioration of the signal distortion, by using a frequency varying circuit utilizing the on-resistance of a diode on the feedback route of a negative feedback amplifier. CONSTITUTION:A transistor Q6 is turned off with a reduction of the control voltage VC, and as a result the diodes Q3 and Q4 are also turned off. Thus the voltage of a resistance which is set in series to a capacitor CO increases virtaully. Accordingly the variance of the feedback quantity caused by the capacitor CO is eliminated, and the gain is reduced only by the feedback quantity of the high band frequency component produced by a capacitor C1. When the voltage VC is increased, the value of the resistance set in series to the capacitor CO is reduced to decrease the feedback quantity of the high band frequency component. As a result, the gain increases at a high band. Such frequency varying circuit is connected to the demodulating circuit of an FM stereo set to eliminate immediately the rasping high band component produced during the stereo-monaural switching mode in accordance with the electronic switching. |
