Patent ID: 7636286

Claim:
A front photo detector for an optical pick-up, comprising: a photo diode unit outputting current proportional to a power of light emitted from one of a plurality of laser diodes; a current-voltage amplifying circuit converting the current output from the photo diode unit into a voltage; and a voltage amplifying circuit amplifying the voltage output from the current-voltage amplifying circuit by a predetermined gain; wherein the photo diode unit comprises an optical device changing a direction of the light emitted from one of the plurality of laser diodes and photo diodes receiving light that is emitted from each of the plurality of laser diodes and passes through the optical device, the current-voltage amplifying circuit comprises a plurality of current-voltage amplifying units, each of which converts current output from a respective photo diode into a voltage, the voltage amplifying circuit separately controls a gain with respect to the current output from the current-voltage amplifying circuit, the voltage amplifying circuit comprises at least one amplifier and separate input variable resistors connected to the output of each of the current-voltage amplifying units, and the plurality of current-voltage amplifying units and the at least one amplifier receive the same reference voltage input.