Patent ID: 7567489

Claim:
A light detector comprising: a light-receiving device that receives a light beam applied from a light source irradiating an optical recording medium with the light beam and that generates detection signals; and a power monitor circuit section that generates a power monitor signal for monitoring output power of the light source in accordance with the detection signals, wherein the light-receiving device includes a plurality of split light-receiving elements, wherein the detection signals are output from the plurality of split light-receiving elements as split detection signals, wherein the power monitor circuit section includes an amplifying circuit that amplifies a signal obtained by adding all the plurality of split detection signals to generate the power monitor signal and that outputs the power monitor signal as a first differential signal and a second differential signal whose polarities are opposite to each other, a fixed resistor that determines a gain of the amplifying circuit, and a position-detecting signal output circuit that generates, in accordance with the plurality of split detection signals, a first position-detecting signal and a second position-detecting signal identifying a position of a light spot on a light-receiving surface of the light-receiving device formed by application of the light beam to the light-receiving surface, and wherein at least the light-receiving device, the amplifying circuit, and the fixed resistor are integrated on an identical semiconductor substrate.