Image Sensor Self-Testing Black Level Correction Circuit
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Solution Overview
Problem
Image sensors face inaccuracies in representing external scenes due to dark current, especially in low light conditions or high temperatures, leading to reduced dynamic range and obscured details in images.
Innovation Solution
The implementation of a self-testing black level correction method using a reset and rotate scheme, channel balance check, flicker check, and sanity check to ensure accurate dark current measurement and correction, enabling continuous frame-by-frame testing and adjustment of black level values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dark current measurement is performed continuously, then black level correction accuracy is improved, but measurement precision deteriorates due to noise accumulation and drift
Solution Approach 1:
The patent performs preliminary actions by measuring black level values at multiple predetermined time points (e.g., start, middle, end of exposure) before final correction is applied. This allows the system to anticipate and compensate for temporal variations in dark current, improving measurement precision without introducing noise accumulation errors
Solution Approach 2:
The patent implements feedback by continuously monitoring black level values at different time points and using this information to dynamically adjust correction parameters. The system compares measurements taken at different times and uses this feedback to optimize the final black level correction, maintaining reliability while improving accuracy
2Measurement precision
If multiple black level measurements are taken at different time points, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the measurement process into discrete time points (start, middle, end of exposure) rather than continuous measurement. This segmentation reduces device complexity by using simple timing controls while improving measurement precision through sampling at critical moments when dark current characteristics are most representative
Solution Approach 2:
The system uses its own operational timing signals (exposure start, midpoint, end) to automatically trigger measurements without requiring external control mechanisms. This self-service approach simplifies the device architecture by leveraging existing timing infrastructure while achieving multiple measurements for improved precision
3Manufacturing precision
If black level correction is applied to all pixels, then image quality is improved, but processing time increases
Solution Approach 1:
The patent applies partial correction by calculating black level values at specific time points (start, middle, end) rather than continuously for the entire exposure duration. This partial action approach improves image quality through targeted correction at critical moments while reducing processing time by avoiding unnecessary continuous computation
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 ensures faithful reproduction of optical characteristics by accurately determining and correcting dark current, thereby enhancing image quality and maintaining image detail even in challenging conditions.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An imaging system comprises an image sensor and black level correction (BLC) circuitry. The image sensor includes an image pixel array adapted to generate an image signal in response to incident light and a dark pixel array adapted to generate a black reference signal representative of a black level value of the image sensor. The BLC circuitry is adapted to adjust the image signal of the image pixel array based, at least in part, on the black reference signal of the dark pixel array. The BLC circuitry includes a plurality of measurement circuits to readout the black reference signal from the dark pixel array to determine the black level value of the image sensor. The BLC circuitry also includes a plurality of calculation circuits to calculate a BLC value based, at least in part, on the black level value determined from the plurality of measurement circuits.