Dual-Photodiode Image Sensor Layout for Precise Focus Readout
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Solution Overview
Problem
Existing image sensors face challenges in accurately focusing and generating high-quality images due to variations in photoelectric conversion efficiencies and signal generation efficiencies across different photodiodes, leading to inconsistencies in focus adjustment and image quality.
Innovation Solution
The image sensor design incorporates a plurality of pixels with two photoelectric conversion units per pixel, where charges are transferred to accumulation units and then read out individually or collectively, ensuring equal capacitance across FD regions to maintain consistent conversion gains and signal generation efficiencies, allowing for precise focus adjustment and improved image data generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charges from multiple photoelectric conversion units are individually transferred to separate accumulation units, then focus adjustment accuracy is improved, but device complexity increases
Solution Approach 1:
The pixel is divided into multiple photoelectric conversion units (first and second photodiodes) that can be individually read out for focus detection, while still allowing combined readout for image capture. This segmentation enables separate charge transfer paths to different accumulation units, improving focus accuracy without requiring complete structural separation of the imaging system.
Solution Approach 2:
Each photoelectric conversion unit is designed to serve dual purposes: individual charge transfer for phase difference detection (focus adjustment) and combined charge transfer for image capture. The accumulation units and transfer mechanisms are configured to handle both individual and collective charge readout, making the system multi-functional and reducing overall device complexity.
2Reliability
If equal capacitance is maintained across all accumulation units, then conversion gain consistency is improved, but manufacturing precision requirements increase
Solution Approach 1:
All accumulation units are designed with equal capacitance values to ensure uniform conversion gain across different charge transfer paths. This equipotential design approach ensures that charges from different photoelectric conversion units are converted to signals with consistent gain, improving reliability and reducing variations in focus adjustment and image quality.
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 the accuracy of focus adjustment and image quality by maintaining equal conversion gains and signal generation efficiencies, reducing variations and improving the overall performance of the image sensor.
Implementation Method 1
a first photoelectric conversion unit that performs photoelectric conversion upon light that has passed through a micro lens and generates a charge; a second photoelectric conversion unit that performs photoelectric conversion upon light that has passed through the micro lens and generates a charge
Data Source
AI summary
An image sensor includes a plurality of pixels each including: a first and a second photoelectric conversion unit that perform photoelectric conversion upon light that has passed through a micro lens and generates a charge; a first accumulation unit that accumulates the charge generated by the first conversion unit; a second accumulation unit that accumulates the charge generated by the second conversion unit; a third accumulation unit that accumulates the charges generated by the first and second conversion units; a first transfer unit that transfers the charge generated by the first conversion unit to the first accumulation unit; a second transfer unit that transfers the charge generated by the second onversion unit to the second accumulation unit; and a third transfer unit that transfers the charges generated by the first and second conversion units to the third accumulation unit.