High-sensitivity large-dynamic-range pixel structure

Abstract

The present invention discloses a high-sensitivity large-dynamic-range pixel structure, comprising a shallow trench isolation STI capacitor, a self-clamping photodiode PPD, a transmission gate TX, a floating diffusion region FD and a reset tube, a source follower SF, and a row selection tube; the self-clamping photodiode PPD is connected with the floating diffusion region FD via the transmission gate TX, and the floating diffusion region FD is connected with the row selection tube via the source follower SF and is connected with the reset tube. The pixel structure is characterized in that: theshallow trench isolation STI capacitor is composed of a heavily doped P well and a silicon oxide isolation trench, an upper polar plate of the shallow trench isolation STI capacitor is connected withthe floating diffusion region FD through a high dynamic range HDR switch, and a lower polar plate is connected to the floating diffusion region FD through a substrate, so that the shallow trench isolation STI capacitor is connected in parallel with the floating diffusion region FD to increase upper capacitance limit of the floating diffusion region FD. The pixel structure also has good performance in noises, size and the like.

Description

technical field [0001] The invention relates to the technical field of CMOS image sensors, in particular to a pixel structure with high sensitivity and large dynamic range. Background technique [0002] Compared with CCD image sensors, CMOS image sensors have obvious advantages in terms of integration and power consumption. In recent years, according to Moore's Law, CMOS process technology has been continuously improved, making the pixel size in the field of image sensors develop in the direction of small size and high performance. . [0003] In the field of CMOS image sensors, dynamic range and sensitivity are very important performance indicators, in which the dynamic range is closely related to the maximum non-saturated signal and the minimum detectable light intensity; the sensitivity is related to the conversion gain of the pixel FD node. With the development of small-sized pixels, the capacitance of the FD node is continuously reduced, which makes the sensitivity cont...

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Problems solved by technology

[0005] Using long and short exposure time technology, this solution exposes the same scene multiple times at different times, and finally fuses the outputs under different exposure times. This solution requires a complex readout signal chain, resulting in high power consumption

[0006] Using the logarithmic photoresponse method and high voltage swing, a transistor working at the subthreshold is added to the pixel to achieve logarithmic compression of the detected light intensity, and a larger detection range can be achieved within the same voltage swing range. But sub-threshold transistors introduce problems with process mismatch, excessive noise in low light, and image smearing

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