Patent ID: 7821682

Claim:
A buffer circuit provided between a photoelectric converting element and an analog signal processing circuit, the buffer circuit comprising: an analog signal buffer configured to input an electric analog signal output from the photoelectric converting element and output the electric analog signal to the analog signal processing circuit; a power supply configured to input a supply voltage to the analog signal buffer; and a delay device provided between the power supply and the analog signal buffer and configured to control a rate of change in the supply voltage input to the analog signal buffer such that rise time or fall time of the supply voltage of the analog signal buffer is made longer than rise time or fall time of a supply voltage of the photoelectric converting element, wherein the delay device comprises: a delay circuit comprising: a resistor having one terminal coupled to the power supply; and a condenser having one terminal coupled to the other terminal of the resistor, wherein the rate of change in the supply voltage input to the analog signal buffer is determined by time constant of the delay circuit.