Patent ID: 7263046
Filing Date: 2007-08-28
Classification: G11B

Abstract:
1. A photo-detector amplifier circuit, which is usable for an optical disk recording and reproducing device and which is capable of switching between different gains respectively corresponding to recording and reproduction each carried out with respect to an optical disk, the photo-detector amplifier circuit comprising: a photo-detector element; a two-stage amplifier, which amplifies an output sent from the photo-detector element and which includes a first-stage amplifier and a second-stage amplifier; first gain switching means capable of switching gains of the first-stage amplifier between the recording and the reproduction; second gain switching means capable of switching gains of the second-stage amplifier in the reproduction; and a transistor whose base is connected to a reference voltage, whose emitter is connected to a junction of an input of the first-stage amplifier and the photo-detector element, and which applies a bias voltage to the photo-detector element so that a voltage at the junction is kept greater than a voltage obtained by subtracting (i) a voltage between the base and the emitter from (ii) the reference voltage.