Photo-detector amplifier circuit for optical disk device

摘要

A two-stage amplifier of a first-stage amplifier 21 and second-stage amplifiers 22 and 23 is provided. A writing mode and reproducing modes are switched in the first-stage amplifier 21 by switching a parallel circuit of a feedback capacitor Cf1w and a feedback resistor Rf1w and a parallel circuit of a feedback capacitor Cf1r and a feedback resistor Rf1r. The second-stage amplifier 23 is provided with feedback resistors Rf22 and Rf23 that are connected to each other in parallel. The feedback resistor Rf23 is connected in the feedback loop by a switch transistor QSW only when reproducing a high-reflective disk. This enables an amplifier gain to be suitably set for each of writing, low-reflective disk reproducing, and high-reflective disk reproducing. As a result, desirable reproducing characteristics can be obtained for the low-reflective disk while accommodating high-speed writing with a large laser power.