Light sensor circuit having source/drain voltage changing-over circuit to minimize afterglow

摘要

Disclosed is a light sensor circuit which works by producing in a photoelectric converting element a photo current proportional to a quantity of incident light falling thereon, converting the photo current into a voltage signal by using a threshold region characteristic of a transistor with a logarithmic output characteristic in a weak inverse state and producing a sensor output corresponding to the voltage signal. The light sensor circuit is provided with an initializing means for removing an electric charge remaining in a parasite capacitor of the photoelectric converting element before detecting light by the same element, thereby achieving a wide dynamic range and obtaining a sensor signal with no afterglow even if it works with a small quantity of incident light.