Patent ID: 8576677
Filing Date: 2013-11-05
Classification: G01J,G11B

Abstract:
1. An optical signal detecting circuit comprising: a quadrant photodetector in which a first photodetector, a second photodetector, a third photodetector, and a fourth photodetector are contiguously arranged counterclockwise in the listed order, each of the photodetectors receiving an optical signal and converting the optical signal into a current signal; and a first current-to-voltage converter, a second current-to-voltage converter, a third current-to-voltage converter, and a fourth current-to-voltage converter, each of which converts the current signal to a voltage signal and outputs the voltage signal, wherein the first current-to-voltage converter converts a current signal into a first voltage signal and outputs the first voltage signal, the current signal being obtained by adding current signals flowing respectively into the first photodetector and the second photodetector, the second current-to-voltage converter converts a current signal into a second voltage signal and outputs the second voltage signal, the current signal being obtained by adding current signals flowing out respectively from the first photodetector and the third photodetector, the third current-to-voltage converter converts a current signal into a third voltage signal and outputs the third voltage signal, the current signal being obtained by adding current signals flowing out respectively from the second photodetector and the fourth photodetector, the fourth current-to-voltage converter converts a current signal into a fourth voltage signal and outputs the fourth voltage signal, the current signal being obtained by adding current signals flowing respectively into the third photodetector and the fourth photodetector, and by applying a first reference voltage, generated by a first reference voltage source, to the second current-to-voltage converter and the third current-to-voltage converter and applying a second reference voltage, generated by a second reference voltage source, which is higher than the first reference voltage, to the first current-to-voltage converter and the fourth current-to-voltage converter, a reverse bias voltage is applied to the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector, the reverse bias voltage being equal to a difference between the second reference voltage and the first reference voltage.