Improvements in or relating to imaging sensors

摘要

Described herein is a pixel readout circuit (100) which provides readout at two sensitivity levels depending on the amount of electrons generated by a pixel photodiode (110) in the circuit. A floating diffusion capacitor (145) operates to store charge up to a saturation value determined by its capacitance and an overflow capacitor (190) is provided in an overflow region (170) for storing charge above the saturation value of the floating diffusion capacitor (145). Readout at a high sensitivity level is provided when the floating diffusion capacitor (145) is not saturated and readout at a lower sensitivity level is provided when there is saturation and subsequent overflow to the overflow region (170). Connection of the floating diffusion capacitor (145) to the overflow capacitor (190) shares the charge over the combined capacitance of the two capacitors and provides readout at a lower sensitivity without loss of charge.