Patent ID: 8115849
Filing Date: 2012-02-14
Classification: G01J,H01L

Abstract:
1. A photo-sensor comprising: a phototransistor for receiving light to generate a photo-current and to output a current produced by amplifying the photo-current; a first MOSFET for detecting the current from the phototransistor; and a second MOSFET having a one non-controlling terminal connected to a base of the phototransistor, to discharge an excessive photo-current in the phototransistor, wherein the second MOSFET is turned OFF when a light quantity incident in the phototransistor is smaller than a predetermined value and a base potential of the phototransistor is at a first potential, and the first MOS FET operates in a saturation region under a condition that the incident light quantity of the phototransistor is larger than a predetermined value, and a gate potential of the second MOSFET is fixed so that the second MOS FET is turned ON, when the base potential of the phototransistor changes from the first potential to a second potential during a sensor operation period for outputting the photocurrent from the phototransistor.