Low dark current pixel with a guard drive active photodiode

摘要

A method and apparatus for reducing thermally generated dark current in a CMOS imaging device is disclosed. A photodiode within the imaging device is kept zero-biased, so that the voltage is equal at both ends of the photodiode. This zero-biasing is accomplished using several different techniques, including, alternatively: a transistor operating at its sub-threshold level; a leaky diode; a short-channel MOSFET; or ramping charge injection.