3T CMOS (Complementary Metal-Oxide-Semiconductor Transistor) pixel unit structure and signal acquisition method thereof

Abstract

The invention provides a 3T CMOS (Complementary Metal-Oxide-Semiconductor Transistor) pixel unit structure, and a method for performing signal acquisition and output. The pixel unit is composed of a pinning photodiode PPD, a level reset tube M1, a signal transport tube M2 and a floating-gate transistor M3. After the M1 finishes unit structure reset, the PPD converts a collected optical signal into an electrical signal, and the electrical signal is transmitted to an FD point connected with the M3 through the M2 and outputted by the M3. The floating-gate transistor of the invention can not only play the role of an output signal buffer, but can also control the output of the pixel unit through the writing and erasing of a floating gate, so that the quantity of cell transistors can be reduced to be 3 without affecting a unit function, and fill factors of the pixel unit can be greatly improved. Since a threshold voltage of the floating-gate transistor under a gate state is far less than a source follower which is served as the output signal buffer in a traditional pixel unit, so that the dynamic range and linearity of the floating-gate transistor are significantly improved on the basis of the traditional pixel unit.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to a novel structure of a 3TCMOS image sensor pixel unit structure and a signal acquisition method thereof. Background technique [0002] The image sensor is an important part of the camera, which is realized by a CMOS or CCD image sensor. [0003] The pixel unit of a conventional CMOS image sensor is the core device of the image sensor to realize light sensing. It usually includes: a photosensitive unit photodiode for photoelectric conversion and a series of peripheral circuits for transmission, signal conversion, amplification and control. [0004] Key specifications for CMOS image sensor design include: fill factor and output voltage magnitude. The size of the fill factor directly determines the photosensitive ability of the pixel. The larger the area of ​​the photodiode and the smaller the area of ​​the readout transistor, the higher the photosensitive sensitivity. [0...

AI Technical Summary

Problems solved by technology

In this structural design, the peripheral circuit of the transistor occupies a large unit area, which affects the further improvement of the fill factor of the pixel unit.

At the same time, the transistor is used as the source follower of the output signal, which also limits the dynamic range of the entire pixel unit and the improvement of linearity

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