Previous amplifier circuit, light-receiving amplifier circuit, and optical pickup apparatus having grounded emitter amplifier circuits each with a grounded emitter transistor

摘要

A previous amplifier circuit of the present invention includes: a grounded emitter amplifier circuit using a grounded emitter transistor connected to a light receiving device; another grounded emitter amplifier circuit using another grounded emitter transistor connected to another light receiving device; and a grounded emitter changing switch to be switched in a manner such that an emitter of the grounded emitter transistors is grounded so as to cause only one of the grounded emitter amplifier circuits to operate. A light-receiving amplifier circuit includes the previous amplifier circuit. An optical pickup apparatus includes the light-receiving amplifier circuit.