Patent ID: 7947940

Claim:
A photoelectric current integrating circuit comprising: a first operational amplifier with a switch and an integrating capacitor connected in parallel between an input terminal and an output terminal thereof; a photodiode that detects a photoelectric current; and a current passing circuit provided between one terminal of said photodiode and the input terminal of said first operational amplifier, for passing the photoelectric current detected at said photodiode while blocking a connection between a parasitic capacitance of said photodiode and said integrating capacitor, wherein said current passing circuit comprises: a second operational amplifier having an inverting input terminal connected to said one terminal of said photodiode and a non-inverting input terminal connected to a constant voltage supply; a transistor having a first terminal connected to the inverting input terminal of said second operational amplifier, a second terminal connected to the input terminal of said first operational amplifier, and a control terminal connected to an output terminal of said second operational amplifier; and a bias current circuit for supplying a bias current between the first terminal and the second terminal of said transistor.