US Patent 7196311 Semiconductor photosensor

A semiconductor photosensor comprises: a semiconductor substrate; a first photodiode formed on the semiconductor substrate; a second photodiode formed on the semiconductor substrate; a first amplifier circuit configured to amplify photocurrent from the first photodiode, the first amplifier circuit being formed on the semiconductor substrate; a second amplifier circuit configured to amplify photocurrent from the second photodiode, the second amplifier circuit being formed on the semiconductor substrate and having an amplifying characteristic substantially identical to that of the first photodiode; an infrared transmissive filter configured to attenuate visible light components relative to infrared light components in incident light, the infrared transmissive filter being provided on the second photodiode; and a subtraction circuit configured to output a difference between an output of the first amplifier circuit and an output of the second amplifier circuit, the subtraction circuit being formed on the semiconductor substrate.