Imaging sensors

摘要

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

主权项

1. A method for operating a light detection circuit comprising a first node, a second node, and a photodiode, the method comprising:
accumulating charge carriers via the photodiode; while the photodiode is accumulating the charge carriers:
(i) connecting a reset voltage to the second node and connecting the second node to the first node;(ii) isolating the second node from the reset voltage and isolating the first node from the second node, thereby generating a reference voltage at the first node; and(iii) sampling the reference voltage; transferring, from the photodiode, a first portion of the charge carriers to the first node and a second portion of the charge carriers to the second node; sampling a first output voltage at the first node represented by the first portion of the charge carriers; distributing the second portion of the charge carriers between the first node and the second node by connecting the first node to the second node; and sampling a second output voltage represented by the first portion of the charge carriers and the second portion of the charge carriers distributed between the first node and the second node.