Abstract: An optical pickup that does not require adjustment of the input/output characteristic of its automatic power control circuit to keep its signal output level at a specific level is proposed. In an optical pickup comprising a light-reception photodiode for converting light reflected from a disk into a current signal, a current-to-voltage converter for converting the current signal outputted from the light-reception photodiode into a voltage signal, a monitoring photodiode for converting part of the light emitted from a semiconductor laser device into a current signal, and an automatic power control circuit for controlling the semiconductor laser device by feedback based on the current signal outputted from the monitoring photodiode, a pair of photodiodes that convert a light signal into a current signal with equal efficiency are used as the light-reception and monitoring photodiodes.

Abstract: A photo diode is connected to an input terminal of an amplifier to which a feedback resistor is connected. An output current of this photo diode flows from the output terminal side of the amplifier through the feedback resistor. The output of the photo diode converted into a voltage is given to the output terminal side of the amplifier. The feedback resistor is formed by a P-type resistor region provided in an N-type resistor land of a semiconductor substrate. In order to apply an inverse bias to the PN junction between the resistor land and resistor region, the resistor land is connected to the output terminal of the amplifier.

Abstract: An optical piece reproduces information from a spiral track of a disk. The pickup device includes the first to sixth photoelectric conversion devices. The first and fourth devices are disposed next to each other along the direction of the track of the disk; the second and third devices are disposed next to each other along the direction of the track. The first and second devices are disposed next to each other along the direction perpendicular to the track direction; the third and fourth devices are disposed next to each other along the direction perpendicular to the track direction. The fifth and sixth devices are disposed on both sides of the unit composed of the first to fourth devices along the track direction. The outputs of the first and third devices are added. The outputs of the second and fourth devices are added. The outputs of the fifth and sixth devices are subtracted from each other. The added and subtracted signals are outputted via output terminals.