Shared Pixel AD Converter Layout for Global Shutter Imaging
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Solution Overview
Problem
In solid-state imaging elements with shared floating diffusion (FD) units, simultaneous charge transfer across multiple pixels for global shutter functionality is challenging, particularly in reducing circuit size while maintaining performance.
Innovation Solution
A solid-state imaging element design where a predetermined number of pixels share an AD converter with a differential pair including a MOS transistor and an amplification transistor, each pixel having a selection transistor for selective AD conversion, enabling simultaneous charge transfer across all pixels at the same timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a plurality of pixels shares an FD unit to reduce circuit size, then circuit size is reduced, but all-pixel simultaneous read (global shutter) cannot be performed
Solution Approach 1:
The pixel array is divided into multiple banks, with each bank having its own independent FD unit. This segmentation allows simultaneous charge transfer from all pixels while maintaining compact circuitry through shared AD converters among banks.
Solution Approach 2:
The AD converter is designed to serve multiple FD units across different pixel banks, enabling a single converter to handle readout from multiple pixel groups. This multi-functionality reduces the total number of AD converters needed while maintaining global shutter capability.
2Productivity
If individual transfer transistors are included for each pixel to enable simultaneous read, then all-pixel simultaneous read is achieved, but the area of photodiode per unit pixel area decreases
Solution Approach 1:
Multiple pixel banks share common AD converter resources and control circuitry. By merging readout functions across banks, the patent reduces redundant circuit elements within each pixel, thereby increasing photodiode area while maintaining global shutter through coordinated bank-level operation.
3Area of stationary object
If a plurality of pixels shares an FD unit, then circuit size is reduced, but performance improvement for global shutter is limited
Solution Approach 1:
The patent implements dynamic control of transfer transistors and selection transistors to enable flexible switching between different readout modes. This dynamic control allows the circuit to achieve both compact size through sharing and high performance through coordinated simultaneous operation of multiple pixel banks.
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 enhances performance by achieving global shutter functionality while reducing circuit size and improving area efficiency, power consumption, and conversion efficiency.
Implementation Method 1
a photodiode 21 that performs 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.