Pixel Sub-Pixel Array for Phase Detection Auto-Focus
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Solution Overview
Problem
Existing image capture devices face challenges in achieving accurate and efficient phase detection auto-focus (PDAF) performance, particularly in low light conditions, due to limitations in pixel configuration and signal correction methods which degrade focus accuracy and increase processing time.
Innovation Solution
The implementation of a pixel array with a 2×2 array of sub-pixels under a microlens, where each sub-pixel is electrically isolated and connected to a shared readout circuit, allowing for simultaneous charge integration and signal correction across multiple photodetectors to provide PDAF information based on both horizontal and vertical edges, enhancing focus detection accuracy and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional pixel configuration is used, then the device complexity is lower, but the PDAF performance and focus detection accuracy are insufficient
Solution Approach 1:
The pixel is divided into multiple photodetectors (e.g., four photodetectors arranged in a 2x2 array) within a single pixel structure. Each photodetector can independently detect light, and by comparing the signals from different photodetectors, the system achieves phase detection for auto-focus. This segmentation enables PDAF functionality while maintaining a compact pixel structure.
Solution Approach 2:
The patent introduces a spatial dimension to PDAF by arranging photodetectors in different positions within the pixel array (e.g., left, right, top, bottom regions). This spatial arrangement allows the system to detect phase information in both horizontal and vertical directions, improving focus detection accuracy without requiring additional pixels.
2Measurement precision
If signal correction methods are applied, then the focus accuracy can be maintained, but the processing time increases
Solution Approach 1:
The patent performs signal correction operations during the image capture process itself rather than as a separate post-processing step. By integrating the correction logic into the readout circuitry and performing corrections while data is being transferred from photodetectors to memory, the system maintains focus accuracy without adding significant processing time delays.
Solution Approach 2:
The pixel structure includes built-in circuitry that automatically performs signal correction and comparison operations. The readout circuitry directly compares signals from different photodetectors and applies corrections as needed, eliminating the need for complex external processing and reducing overall processing time while maintaining accuracy.
3Measurement precision
If multiple image sensors are used, then the image quality can be improved, but the device complexity and processing requirements increase
Solution Approach 1:
The patent makes regular image sensor pixels multi-functional by enabling them to perform both standard image capture and PDAF operations. By configuring photodetectors within each pixel to serve dual purposes (image sensing and phase detection), the system achieves improved image quality and focus accuracy without requiring separate dedicated PDAF sensors or multiple image sensors.
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 PDAF performance by reducing the need for signal correction and increasing the resolution of image sensors, enabling faster and more accurate focus adjustment in various lighting conditions, including low light scenarios.
Implementation Method 1
A microlens may be disposed over the array of photodetectors for the pixel. The peripheral portion of the microlens may be configured to redirect at least a portion of light incident on the peripheral portion toward a corresponding peripheral portion of the imaging area.
Implementation Method 2
The imaging area may include a plurality of pixels. Multiple pixels of the plurality of pixels may each include a two-dimensional array of photodetectors
Data Source
AI summary
An image capture device, pixel, and method of determining a focus setting for an image capture device are described. The image capture device includes an imaging area and a pixel readout circuit. The imaging area includes a plurality of pixels. The plurality of pixels includes multiple pixels in which each pixel of the multiple pixels includes a two-dimensional array of photodetectors and a microlens. Each photodetector in the array of photodetectors for a pixel is electrically isolated from each other photodetector in the array of photodetectors. A microlens is disposed over the array of photodetectors for the pixel. The pixel readout circuit includes, per pixel, a shared readout circuit associated with the array of photodetectors for the pixel and a set of charge transfer transistors. Each charge transfer transistor is operable to connect a photodetector in the array of photodetectors to the shared readout circuit.