PDAF Pixel Array with Variable Photodiode Area Ratios
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Solution Overview
Problem
Compact and cost-effective digital cameras face challenges in achieving fast and accurate autofocus due to limitations in phase-detection autofocus technology, which is typically feasible in more advanced cameras with dedicated sensors.
Innovation Solution
The implementation of a PDAF pixel array with dual-diode pixels, where the ratio of inner to outer photodiode areas varies with distance from the center, enhancing angular sensitivity and accuracy by optimizing the design of the PDAF pixel layout and photodiode widths to improve phase-detection autofocus accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated phase-detection sensor is used, then autofocus accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the imaging function and phase-detection function into a single integrated pixel array. Each pixel in the array serves dual purposes: capturing image data and detecting focus status through its photodiodes. This eliminates the need for a separate dedicated phase-detection sensor while maintaining autofocus capability.
Solution Approach 2:
The imaging sensor pixels are designed to perform multiple functions simultaneously. The photodiodes within each pixel detect both the intensity of incident light for imaging purposes and the angular information for phase-detection autofocus. This multi-functionality reduces overall system complexity while achieving both imaging and focus detection.
2Device complexity
If conventional PDAF pixel design is used, then device complexity is reduced, but autofocus accuracy deteriorates
Solution Approach 1:
The patent applies different photodiode configurations to different regions of the pixel array based on their specific requirements. Pixels at different positions have photodiodes with different area ratios optimized for their particular angular detection needs. This localized optimization improves overall accuracy without requiring a completely different design for every pixel.
Solution Approach 2:
The patent optimizes the area ratio parameter of photodiodes within each pixel based on their position in the array. By varying this geometric parameter across different pixel locations, the system achieves improved angular sensitivity and focus detection accuracy while maintaining a relatively simple overall pixel structure.
3Manufacturing precision
If fixed photodiode area ratio is used, then manufacturing precision is improved, but autofocus accuracy deteriorates
Solution Approach 1:
Instead of using a uniform photodiode area ratio across all pixels, the patent implements location-specific ratios that are optimized for each pixel's position in the array. This allows each pixel to have the optimal geometric configuration for its angular detection requirements while maintaining manufacturability through systematic variation rather than complete customization.
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 solution enhances the accuracy and speed of phase-detection autofocus in compact cameras by optimizing the PDAF pixel array design, ensuring reliable and fast focusing capabilities comparable to more advanced camera systems.
Implementation Method 1
Dual-diode PDAF pixel 200 includes photodiodes 211 and 212 having a common color filter 221 and microlens 230
Data Source
AI summary
A phase-detection auto-focus (PDAF) pixel array includes a first pixel and a second pixel. The first pixel, located at a first distance from a center of the PDAF pixel array, includes a first inner photodiode and a first outer photodiode with respect to the center. The first inner photodiode and the first outer photodiode occupy respectively a first inner area and a first outer area. The first inner area divided by the first outer area equals a first ratio. The second pixel, located at a second distance from the center that exceeds the first distance, includes a second inner photodiode and a second outer photodiode with respect to the center. The second inner photodiode and the second outer photodiode occupy respectively a second inner area and a second outer area. The second inner area divided by the second outer area equals a second ratio, which exceeds the first ratio.