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

A light-receiving amplifier circuit, comprising:

• a previous amplifier circuit including:
• a plurality of light receiving devices, each receiving a light signal, converting the light signal into current, and outputting the current, the light signal being incident on only one of the plurality of light receiving devices;
• a plurality of grounded emitter amplifier circuits, each amplifying, by use of a grounded emitter transistor, the current thus outputted and outputting the current thus amplified, the plurality of grounded emitter amplifier circuits being provided one by one for the plurality of light receiving devices;
• a first switch to be switched in a manner such that an emitter of a grounded emitter transistor connected to a light receiving device on which the light signal is incident is grounded so as to cause only one of the plurality of grounded emitter amplifier circuits to operate;
• an active load of the plurality of grounded emitter amplifier circuits;
• and
• an output circuit to receive an output of the plurality of grounded emitter amplifier circuits, and to produce an output by use of an emitter follower.

An optical pickup apparatus, comprising:

• a light-receiving amplifier circuit including:
• a previous amplifier circuit including:
• a plurality of light receiving devices, each receiving a light signal, converting the light signal into current, and outputting the current, the light signal being incident on only one of the plurality of light receiving devices;
• a plurality of grounded emitter amplifier circuits, each amplifying, by use of a grounded emitter transistor, the current thus outputted and outputting the current thus amplified, the plurality of grounded emitter amplifier circuits being provided one by one for the plurality of light receiving devices;
• a first switch to be switched in a manner such that an emitter of a grounded emitter transistor connected to a light receiving device on which the light signal is incident is grounded so as to cause only one of the plurality of grounded emitter amplifier circuits to operate;
• an active load of the plurality of grounded emitter amplifier circuits;
• and
• an output circuit to receive an output of the plurality of grounded emitter amplifier circuits, and to produce an output by use of an emitter follower.