High Dynamic Range CMOS Pixel and Method of Operating Same

Abstract

A method of operating a CMOS pixel is disclosed. The CMOS pixel includes a photodiode (PPD), a transfer gate coupled to the PPD, and an anti-blooming drain coupled to the transfer gate. A potential barrier is formed between a potential well underlying the PPD and the transfer gate. Charge is accumulated in the potential well in response to electromagnetic radiation during a first integration time. Excess charge is removed from the potential well to the anti-blooming drain that exceeds the first potential barrier. A size of the potential barrier is increased. Charge is accumulated in the potential well during a second integration time.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. utility application No. 13 / 223,991 filed Sep. 1, 2011, which claims the benefit of U.S. provisional patent application No. 61 / 379,504 filed Sep. 2, 2010, the disclosures of which are incorporated herein by reference in their entirety.FIELD OF THE INVENTION[0002]The invention relates generally to imaging devices. More specifically, the invention relates to improving the dynamic range of CMOS pixels.BACKGROUND OF THE INVENTION[0003]CMOS image sensors first came to the fore in relatively low-performance applications where shuttering was not required, scene dynamic range was low, and moderate to high noise levels could be tolerated. A CMOS sensor technology enabling a higher level of integration of an image array with associated processing circuits would be beneficial to many digital applications such as, for example, in cameras, scanners, machine vision systems, vehicle navigation systems, video te...

AI Technical Summary

Benefits of technology

[0013]In an embodiment, increasing the size of the potential barrier may include increasing a magnitude of a potential applied to the transfer gate from a first level before the first integration time to a second level at the second integration time. The size of the potential barrier may be increased non-linearly as a function of time. The size of the potential barrier may increased in discrete steps over time or continuously over time. The second integration time may be shorter than the first integration time.

[0014]In an embodiment, the method may further include operating the transfer gate with narrow pulses to momentarily reduce well capacity of the PPD. Voltage applied to the transfer gate may be adjusted for each subsequent pulse, resulting in less reduction of well capacity with respect to the previous pulse. Spacing in time for the pulses may be reduced for a subsequent sub-integration time.

Problems solved by technology

Thus, dynamic range is limited.

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