Four-Photodiode Pixel with Shared Microlens for Phase Detection
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Solution Overview
Problem
The miniaturization of CMOS image sensors has led to reduced pixel photosensitivity and dynamic range, challenging advanced features like phase difference detection autofocus, as the decreased pixel size diminishes light absorption and signal noise, making it difficult to effectively calculate focus shifts.
Innovation Solution
The implementation of an array of pixel cells with four maskless phase detection photodiodes sharing a single microlens and filter, where light is collected in two directions by adjacent pairs of photodiodes, and a light guide structure is used between pairs to enhance signal discrimination and resolution, allowing for improved autofocus functionality and increased image sensor resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pixel size is decreased to increase resolution, then image sensor resolution is improved, but pixel photosensitivity and signal to noise ratio deteriorate
Solution Approach 1:
The patent combines four photodiodes into a single pixel unit that shares one readout amplifier, microlens, and color filter. This merging approach allows the pixel to function as both a high-resolution imaging element and a phase detection element, effectively increasing photosensitivity by pooling light collection from multiple photodiodes while maintaining high resolution through the shared readout infrastructure.
Solution Approach 2:
The pixel design enables dual functionality: the same four photodiodes and shared components can operate in full-array readout mode for high-resolution imaging and in phase detection mode for autofocus. This multi-functionality eliminates the need for separate dedicated phase detection pixels, thereby maximizing photosensitivity across all pixels while supporting both imaging and autofocus operations.
2Manufacturing precision
If pixel size is decreased to increase resolution, then image sensor resolution is improved, but dynamic range deteriorates
Solution Approach 1:
By merging four photodiodes into a single functional pixel unit with shared readout components, the patent effectively increases the light collection area per pixel. This allows smaller physical pixels to achieve equivalent or superior dynamic range by pooling photons across multiple photodiodes, thereby maintaining wide dynamic range despite reduced individual pixel size.
3Measurement precision
If masked photodiodes are used for phase detection, then phase difference detection capability is improved, but signal to noise ratio deteriorates
Solution Approach 1:
The patent removes the mask structure from the photodiodes entirely, using maskless phase detection. Instead of physically blocking light with masks, the system uses the geometric arrangement of four photodiodes under a single microlens to detect phase differences. This extraction of the mask component eliminates light loss and noise associated with masking while preserving phase detection capability through the photodiode array geometry.
4Adaptability or versatility
If separate autofocus readout and full resolution readout are conducted with different photodiode combinations, then autofocus functionality is achieved, but device complexity increases
Solution Approach 1:
The patent designs a universal pixel structure where the same four photodiodes and shared components serve both full-resolution imaging and phase detection autofocus functions. By switching between readout modes rather than using separate hardware paths, the system achieves dual functionality without duplicating readout circuits, thereby reducing overall device complexity while maintaining versatile operation.
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 enhances autofocus performance by combining signals from photodiode pairs during autofocus and provides full resolution imaging capabilities, enabling autofocus information from the entire sensor array rather than limited photodiode pairs, thus overcoming the limitations of reduced photodiode size.
Implementation Method 1
the two adjacent pairs of photodiodes are positioned under the single microlens such that light incident in a first direction is collected in a first pair of photodiodes and light incident in a second direction is collected in a second pair of photodiodes
Implementation Method 2
the image sensor converts the light into electrical signals
Data Source
AI summary
A pixel cell has four maskless phase detection photodiodes sharing the same readout amplifier, microlens and filter color. The four photodiodes are configured to operate in two adjacent pairs wherein the two adjacent pairs of photodiodes are separated by a light guide and are positioned under the single microlens such that light incident in a first direction is collected in a first pair of photodiodes of the two adjacent pairs of photodiodes and light incident in a second direction is collected in a second pair of photodiodes of the two adjacent pairs of photodiodes. The microlens has a plano-convex shape which causes light to be incident in two directions on photodiodes positioned under each of two sides of the microlens.