Non-uniform Light Shields for Image Sensor Channel Calibration
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Solution Overview
Problem
Image sensors with multiple output channels face non-uniformity issues due to performance mismatches between channels, which are challenging to calibrate accurately, especially under varying environmental conditions, and existing calibration methods are costly and complex, introducing noise and requiring additional power supplies.
Innovation Solution
The use of non-uniform light shields over reference pixels in sub-arrays to generate correction factors that compensate for channel differences, eliminating mismatches by comparing signal outputs and applying correction factors to all pixel signals, without the need for extra power supplies or complex fabrication processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If known test targets are used to calibrate mismatches between multiple outputs, then calibration can be performed during camera manufacturing, but the accuracy of calibration is compromised due to sensitivity to environmental conditions such as temperature, power supply biases, or clock timing
Solution Approach 1:
The image sensor performs self-calibration using its own reference pixels and non-uniform light shields, eliminating the need for external test targets and manual calibration procedures. The sensor automatically determines correction factors by comparing signals from reference pixels with known non-uniform light shielding patterns, making the calibration process independent of environmental conditions.
Solution Approach 2:
The non-uniform light shields are pre-fabricated into the image sensor structure during manufacturing, creating built-in reference patterns that enable subsequent calibration operations. These permanent light shielding structures provide stable, reproducible reference signals that can be used for calibration at any time without requiring external test equipment or specific environmental conditions.
2Measurement precision
If electrical-injection structures are used to calibrate output channels, then calibration can be performed by injecting signals into phases, but additional DC power supplies are required and the fabrication process becomes more costly and complex
Solution Approach 1:
The patent removes the complex electrical-injection structures, additional DC power supplies, and varied barrier regions from the calibration system. Instead, it uses only the standard pixel structure with added non-uniform light shields, extracting the essential calibration function from the complicated electrical injection mechanism and implementing it through optical means alone.
Solution Approach 2:
The patent replaces the electrical-injection calibration mechanism with an optical calibration approach using non-uniform light shields. Instead of using electrical signals injected through diodes and barrier regions, the system uses optical shielding patterns to create known signal variations in reference pixels, substituting a simpler optical system for a complex electrical system.
3Measurement precision
If electrical injection process is used for calibration, then output channels can be calibrated, but noise is introduced by the electrical injection process itself
Solution Approach 1:
The patent replaces the electrical injection process with an optical calibration method. Non-uniform light shields create known signal variations in reference pixels through optical blocking patterns, eliminating the need for electrical signal injection. This substitution removes the noise generated by electrical injection while maintaining the ability to determine accurate correction factors for output channel calibration.
4Speed
If multiple output channels are used to achieve faster frame rates, then image sensor speed increases, but differences or mismatches between output channels introduce non-uniform effects
Solution Approach 1:
The patent implements a feedback-based calibration system where correction factors are determined by comparing signals from reference pixels with known non-uniform light shielding patterns. These correction factors are then applied to compensate for mismatches between multiple output channels, creating a closed-loop system that actively corrects for channel non-uniformity and maintains image quality across all channels.
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 effectively compensates for channel mismatches, improving image sensor accuracy and reducing costs and complexity by eliminating the need for additional power supplies and simplifying the calibration process, while maintaining high statistical accuracy across the dynamic range of the image sensor.
Implementation Method 1
A continuous non-uniform light shield overlies each reference pixel in a row or column of reference pixels
Data Source
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Figure 5~6A
AI summary
An image sensor includes a pixel array divided into two or more corresponding sub-arrays. The pixel array includes an imaging area having a plurality of pixels and one or more reference areas each having a plurality of reference pixels. A continuous non-uniform light shield overlies, or individual non-uniform light shields overlie, each reference pixel in a row or column of reference pixels. An image sensor can include one or more rows or columns of reference pixels. An output channel is electrically connected to each sub-array for receiving the signals generated by the plurality of pixels and reference pixels in each sub-array. The pixel signals generated by the reference pixel pairs in one or more rows or columns in corresponding sub-arrays are used to determine one or more correction factors that compensate for the differences or mismatches between the output channels.