| 摘要 |
A volume control signal voltage is applied to one terminal of a resistor 50, flowing a current corresponding to the volume control signal voltage through the resistor 50. The other terminal of the resistor 50 is connected to the emitter of a transistor 54, in which a constant voltage is applied to the base. An input side transistor of a current mirror 57 is connected to the collector of the transistor 54, and constant current transistors 55 and 56 are connected downstream the transistor 54 and the output side transistor of the current mirror 57. The same current as through the resistor 50 is output from the upstream side of the constant current transistor 56. According to this output current, a GCA 102 is operated through a differential amplifier 58. The gain of the GCA 102 can thus be smoothly varied according to the volume control signal voltage. It is thus possible to obtain smooth variation of the attenuation of a signal under control according to changes in the volume control signal voltage.
|
