| 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 Cf 1 w and a feedback resistor Rf 1 w and a parallel circuit of a feedback capacitor Cf 1 r and a feedback resistor Rf 1 r. The second-stage amplifier 23 is provided with feedback resistors Rf 22 and Rf 23 that are connected to each other in parallel. The feedback resistor Rf 23 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.
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