Shared Pixel ADC Structure for Global Shutter Image Sensors
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Solution Overview
Problem
In imaging elements with shared floating diffusion (FD) units, simultaneous charge transfer from photodiodes to the FD unit across all pixels is challenging, making it difficult to achieve global shutter functionality while minimizing circuit size.
Innovation Solution
A solid-state imaging element design where a predetermined number of pixels share an AD converter, including a differential pair of MOS transistors and an amplification transistor, with each pixel equipped with a selection transistor to enable simultaneous AD conversion and global shutter operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a plurality of pixels shares an FD unit, then the area of photodiode per unit pixel area is increased, but all-pixel simultaneous read cannot be performed
Solution Approach 1:
The pixel array is divided into multiple banks, with each bank having its own dedicated FD unit. This segmentation allows simultaneous charge transfer from all pixels while maintaining the benefit of shared readout circuitry. Each bank can operate independently, enabling global shutter functionality across the entire array.
Solution Approach 2:
The patent introduces a bank dimension to organize pixels, moving from a simple shared FD structure to a multi-bank hierarchical structure. This dimensional organization allows parallel operation of multiple FD units while maintaining area efficiency through shared peripheral circuitry.
2Reliability
If all-pixel simultaneous read is performed, then global shutter functionality is achieved, but the size of circuit increases
Solution Approach 1:
Multiple banks share common peripheral circuitry including ADCs, output buffers, and control logic. This merging of resources allows global shutter functionality to be achieved without proportionally increasing the total circuit area, as the shared circuitry serves multiple banks simultaneously.
Solution Approach 2:
The peripheral circuitry is designed to be universal and multi-functional, serving multiple banks of pixels. The ADCs and output circuitry can handle data from any bank, reducing the need for dedicated circuitry for each bank and thereby minimizing overall circuit size while maintaining global shutter capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design allows for efficient charge transfer and AD conversion across all pixels at the same timing, improving performance by reducing circuit size and enhancing area efficiency, power consumption, and conversion efficiency.
Implementation Method 1
a photoelectric conversion unit configured to perform photoelectric conversion
Data Source
AI summary
A solid-state imaging element and an electronic device are provided. A pixel at least includes a photoelectric conversion unit that performs photoelectric conversion, an FD unit to which charge generated in the photoelectric conversion unit is transferred, and an amplification transistor that has a gate electrode to which the FD unit is connected. A reference signal is input to a MOS transistor. The reference signal is referred to when AD conversion is performed on a pixel signal according to an amount of light received by the pixel. Then, a shared structure is employed in which a predetermined number of pixels share an AD converter that includes a differential pair including the MOS transistor and the amplification transistor. Each of the pixels is provided with a selection transistor that is used to select a pixel for which AD conversion is performed on the pixel signal.