Dark Pixel Array for Local Dark Current Compensation
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Solution Overview
Problem
Existing image sensors face challenges in accurately compensating for dark shading, particularly in CMOS image sensors, due to non-uniform dark signals across the pixel array, which requires expensive calibration and complex mechanical setups, making them unsuitable for small cameras.
Innovation Solution
Incorporating a pixel array with an active pixel block and an optical black pixel block, along with a compensation circuit that uses dark pixels to generate local and global dark currents, allowing for precise compensation of local dark current in each active pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mechanical shutter and image buffer are used to capture dark frame for compensation, then dark signal measurement is possible, but device complexity and size increase making it unsuitable for small cameras
Solution Approach 1:
The patent extracts the dark signal measurement function from the mechanical shutter system by dedicating specific pixels (dark pixels) within the image sensor array itself to measure dark current, eliminating the need for external mechanical shutters and image buffers while maintaining measurement capability
Solution Approach 2:
The image sensor array serves multiple functions: active pixels capture image signals while dark pixels simultaneously measure dark signals, allowing the same sensor structure to perform both imaging and dark signal measurement without requiring separate dedicated components
2Device complexity
If dark signal is evaluated using peripheral covered pixels, then measurement setup is simplified, but measurement precision deteriorates because dark signal is not uniform across the pixel array
Solution Approach 1:
The patent applies local quality by placing dark pixels at multiple locations throughout the pixel array rather than only at periphery, allowing dark signal measurement to reflect local variations in dark current across different regions of the sensor, thereby improving measurement precision while maintaining relatively simple implementation
3Measurement precision
If an accurate dark signal model is setup for the entire pixel array, then measurement precision improves, but manufacturing cost increases due to required calibration for each sample
Solution Approach 1:
The patent enables the sensor to self-measure its own dark signal characteristics through dedicated dark pixels during normal operation, eliminating the need for external calibration equipment and processes for each sample while maintaining accurate dark signal modeling across the pixel array
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 enables effective compensation of dark shading, improving image quality by adjusting the voltage level in the active pixel block and reducing the need for complex mechanical setups, making it suitable for small cameras and reducing calibration costs.
Implementation Method 1
at least one dark pixel configured to generate a local dark current... The at least one dark pixel may include a light blocking layer formed between a photodiode and a microlens
Data Source
AI summary
A pixel array for an image sensor is provided. The pixel array includes a dark pixel which is configured to detect a local dark current in an active pixel block. The dark pixel is distinguished from an optical black pixel block which is arranged around the active pixel block and is configured to detect a global dark current. The pixel array is configured to compensate for dark shading, which is not compensated through global dark current compensation, using the local dark current output from the dark pixel which is arranged within the active pixel block.