Patent ID: 8664580

Claim:
An optical sensor comprising: a photodiode with its anode grounded; a current-voltage conversion section having one end connected to a cathode of the photodiode; a current source having one end connected to the other end of the current-voltage conversion section; a power supply section for applying a constant voltage to the other end of the current source; and a grounded-emitter or grounded-source output transistor having a base or gate connected to the cathode of the photodiode and a collector or drain connected to one end of the current source, wherein the current-voltage conversion section includes a semiconductor device group having n PN junctions (where n is an integer of 2 or more) connected in series so that their forward directions are directed toward the photodiode side, and a photocurrent which flows from a connecting point between the current-voltage conversion section and the current source to the photodiode is converted into a voltage and outputted as a photoelectric conversion signal.