Image Sensor Shared Floating Diffusion Readout
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Solution Overview
Problem
Conventional image sensors require multiple readouts for phase detection autofocus (PDAF) and image sensing, leading to increased noise and reduced frame rates due to the need for multiple correlated double sampling (CDS) readouts.
Innovation Solution
A photodiode array configuration with shared floating diffusion and analog-to-digital converter (ADC) operations that perform three readouts instead of four, allowing for simultaneous PDAF and image sensing data acquisition, reducing noise and improving frame rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple readouts are performed for PDAF and image sensing, then both PDAF and image data can be acquired, but noise increases and frame rate decreases
Solution Approach 1:
The patent merges PDAF readout and image sensing readout into a single unified readout operation. By combining the charge transfer paths and using a shared floating diffusion region, the system performs both PDAF measurement and image data acquisition simultaneously during one readout cycle, eliminating the need for separate readout operations and thereby improving frame rate while maintaining noise performance
Solution Approach 2:
The patent implements multi-functionality by designing the pixel structure and readout circuitry to serve dual purposes. The same photodiode array and readout path are used for both PDAF focus detection and image sensing, allowing a single readout operation to fulfill multiple functions and thereby increasing productivity without sacrificing measurement precision
2Adaptability or versatility
If multiple readouts are performed for PDAF and image sensing, then both PDAF and image data can be acquired, but the number of readout operations increases
Solution Approach 1:
The patent merges PDAF readout and image sensing readout into a single unified readout operation. By combining the charge transfer paths and using a shared floating diffusion region, the system performs both PDAF measurement and image data acquisition simultaneously during one readout cycle, eliminating the need for separate readout operations and thereby improving frame rate while maintaining noise performance
Solution Approach 2:
The patent implements multi-functionality by designing the pixel structure and readout circuitry to serve dual purposes. The same photodiode array and readout path are used for both PDAF focus detection and image sensing, allowing a single readout operation to fulfill multiple functions and thereby increasing productivity without sacrificing measurement precision
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 approach enhances noise performance and frame rate by reducing the number of readouts required, resulting in noise closer to the single CDS readout noise and frame rate performance approximately 2.3 times that of conventional methods.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An imaging device includes a plurality of photodiodes arranged in a photodiode array to generate charge in response to incident light. The plurality of photodiodes includes first and second photodiodes. A shared floating diffusion receives charge transferred from the first and second photodiodes. An analog to digital converter (ADC) performs a first ADC conversion to generate a reference readout in response to charge in the shared floating diffusion after a reset operation. The ADC is next performs a second ADC conversion to generate a first half of a phase detection autofocus (PDAF) readout in response to charge transferred from the first photodiode to the shared floating diffusion. The ADC then performs a third ADC conversion to generate a full image readout in response to charge transferred from the second photodiode combined with the charge transferred previously from the first photodiode in the shared floating diffusion.