Shared Four-Photodiode Pixel Readout for PDAF and Binning
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Solution Overview
Problem
CMOS image sensors with phase detection pixels face challenges in autofocus performance due to decreased pixel size, leading to reduced light absorption and signal noise, which limits image sensor resolution and dynamic range.
Innovation Solution
The implementation of an imaging system with four photodiodes sharing a common readout amplifier, row select transistor, microlens, and color filter, allowing for horizontal or vertical binning, or both, to enhance autofocus functionality and improve frame rate and slow-motion imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is decreased to increase image sensor resolution, then image sensor resolution is improved, but light absorption and signal quality are reduced
Solution Approach 1:
The patent combines four photodiodes into a single pixel unit, allowing them to share common readout amplifiers, row select transistors, microlenses, and color filters. This merging approach increases the effective light-gathering area while maintaining high resolution through the shared readout infrastructure.
Solution Approach 2:
The shared readout amplifier and control circuitry serve multiple photodiodes simultaneously, enabling the system to maintain high resolution while reducing the number of individual readout paths needed. This multi-functionality reduces circuit complexity and improves light absorption efficiency.
2Measurement precision
If pixel size is decreased to increase image sensor resolution, then image sensor resolution is improved, but signal noise increases
Solution Approach 1:
By combining signals from four photodiodes that share common readout circuitry, the patent increases the effective signal strength while maintaining resolution. The shared readout amplifier processes combined signals, improving signal-to-noise ratio compared to individual small photodiodes.
3Extent of automation
If phase detection pixels use masked photodiodes for autofocus, then autofocus capability is improved, but pixel signal is reduced
Solution Approach 1:
The patent combines four photodiodes in a 2x2 arrangement where adjacent photodiodes share microlenses and color filters. This configuration provides phase detection capability through differential measurement while increasing total light absorption area, thereby improving signal strength compared to single masked photodiodes.
4Measurement precision
If standard readout mode is used, then image quality is maintained, but frame rate is limited
Solution Approach 1:
The patent implements binning modes where adjacent pixel units combine their signals before readout. This merging approach reduces the total number of readout operations needed, thereby increasing frame rate while maintaining adequate image quality through signal combination.
Solution Approach 2:
The patent provides dynamic readout mode selection, allowing the system to switch between full-resolution mode and binned mode with higher frame rates. This dynamic adaptability enables optimization between image quality and frame rate based on application requirements.
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 configuration improves autofocus accuracy, increases image sensor resolution, and enhances dynamic range by effectively combining signals from photodiodes during phase detection autofocus, resulting in improved frame rates and slow-motion image capture.
Implementation Method 1
The two adjacent photodiodes are positioned under the single microlens such that light incident in a first direction is collected in a first photodiode of the two adjacent photodiodes and light incident in a second direction is collected in a second photodiode of the two adjacent photodiodes.
Implementation Method 2
The image sensor converts the light into electrical signals.
Data Source
AI summary
An imaging system with an array of pixel cell units having four photodiodes sharing the same readout amplifier, row select transistor, microlens and filter color. Some pixel cell units provide a phase detection autofocus function. The imaging system provides the option of imaging with phase detection autofocus and with or without horizontal or vertical binning readout modes, or both simultaneously, to form an a full resolution image of the target scene with improved effective frame rate and improved slow motion imaging.