A 3t CMOS pixel unit structure and its signal acquisition method

Abstract

The invention proposes a 3T CMOS pixel unit structure and a method for signal acquisition and output thereof. The pixel unit is composed of a pinned photodiode PPD, a level reset transistor M1, a signal transmission transistor M2 and a floating gate transistor M3. After M1 completes the reset of the unit structure, PPD converts the collected optical signal into an electrical signal, transmits it to the FD point connected to M3 through M2, and outputs it through M3. The floating gate transistor of the present invention can not only serve as an output signal buffer, but also control the output of the pixel unit by writing and erasing the floating gate, thereby reducing the number of unit transistors to three without affecting the unit function. The fill factor of the pixel unit is greatly improved. Since the threshold voltage of the floating gate transistor in the gate state is much smaller than the source follower used as the output signal buffer in the traditional pixel unit, its dynamic range and linearity 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 3T CMOS image sensor pixel unit structure and a signal collection 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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