Patent ID: 6815685
Filing Date: 2004-11-09
Classification: G01J

Abstract:
A photodetector comprising:a zone of a semiconductor material suitably doped to collect photogenerated charges, coupled between a ground voltage and a sensing node; a capacitance coupled in parallel to the zone of semiconductor material, between the ground voltage and the sensing node; a metal oxide semiconductor (MOS) transistor coupled at its source and drain between the sensing node and a supply voltage; and a means for applying a predetermined voltage to the gate of the transistor; in which, if the capacitance has been charged so that the magnitude of a voltage at the sensing node is greater than a transition voltage magnitude and a predetermined gate voltage is applied so that the transistor is non-conductive, then a photocurrent of a magnitude dependent on the intensity of radiation incident upon the zone of semiconductor material flows therethrough, discharging the capacitance and causing the sensing node voltage to vary substantially linearly with the photocurrent magnitude until the sensing node voltage reaches the transition voltage, and thereafter the transistor becomes conductive and the photocurrent generates a sensing node voltage which changes substantially logarithmically with the photocurrent magnitude.