PDAF Pixel Micro-Lens Alignment for Focus Accuracy
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Solution Overview
Problem
Conventional image sensors with integrated phase detection auto-focus (PDAF) pixels face challenges in maintaining accurate focus offset measurements due to the offset positioning of micro-lenses and color filters, which degrades image quality and focus accuracy, especially at the periphery, and require time-consuming calibration after packaging each die.
Innovation Solution
The solution involves designing an image sensor pixel array with PDAF pixels in parallel edge regions and image pixels at the center, where PDAF pixels share a common micro-lens aligned with their light receiving areas, allowing for accurate focus offset measurement without packaging, and a method to generate an angular response curve by averaging readout signals from left and right side PDAF pixels to calibrate the focus offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If micro-lens and color filter are formed in offset position above light receiving element to improve light collection rate for oblique light, then light collection rate is improved, but accuracy of measured degree of lens focus offset is degraded
Solution Approach 1:
The patent applies different micro-lens offset positions for different regions of the sensor. Image pixels in the central region have micro-lenses positioned to optimize for oblique light, while PDAF pixels have micro-lenses aligned directly above them to maintain focus measurement accuracy. This localized differentiation resolves the contradiction by allowing each pixel type to have optimal micro-lens positioning for its specific function.
2Device complexity
If PDAF pixels are integrated with image pixels in the same image sensor, then device complexity is reduced, but focus accuracy at periphery is degraded
Solution Approach 1:
The patent implements region-specific micro-lens positioning within the integrated sensor array. In the central region where image pixels dominate, micro-lenses are offset to improve oblique light collection. In peripheral regions where PDAF pixels are located, micro-lenses are aligned directly above PDAF pixels to maintain accurate focus offset measurements. This spatially differentiated approach maintains both integration benefits and measurement accuracy.
3Manufacturing precision
If conventional offset positioning is used for micro-lens to improve peripheral light collection, then image quality at periphery is improved, but PDAF pixel calibration accuracy is degraded
Solution Approach 1:
The patent segments the sensor into distinct functional regions with different micro-lens positioning strategies. The central image pixel region uses offset micro-lenses for improved light collection, while peripheral PDAF pixel regions use aligned micro-lenses for accurate focus measurement. This segmentation allows each region to be optimized for its primary function without compromising the other.
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 the accuracy of lens focus adjustment and improves image quality by maintaining focus accuracy across the image sensor, allowing for pre-packaging calibration of PDAF pixels on the wafer, reducing measurement time and improving peripheral light collection rates.
Implementation Method 1
a micro-lens and color filter in an image sensor disclosed in U.S. Pat. No. 7,411,180 B2 is formed in an offset position above a light receiving element as a countermeasure for shortening of exit pupil distance
Implementation Method 2
phase detection autofocus (PDAF) directly measures the degree of lens focus offset by comparing light passing through one portion of the imaging objective, e.g., the left portion, with light passing through another portion of the imaging objective, e.g., the right portion
Data Source
AI summary
An image sensor pixel array comprises a center region and two parallel edge regions, wherein the center region is between the two parallel edge regions. The center region comprises a plurality of image pixels disposed along first sub-array of rows and columns, wherein each of the plurality of image pixels comprises a first micro-lens (ML) formed at an offset position above a first light receiving element as a countermeasure for shortening of exit pupil distance of the image pixel in the center region, and each of the two parallel edge regions comprises a plurality of phase detection auto-focus (PDAF) pixels disposed along second sub-array of rows and columns, wherein each of the plurality of PDAF pixels comprises a second micro-lens (ML) formed at an alignment position above a second light receiving element; and at least one of the PDAF pixels is located at a distance away from center of the edge region to receive incident light along an injection tilt angle.