Image Sensor Active and Black Pixel Gain Adjustment
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Solution Overview
Problem
MOS image sensors face challenges in accurately eliminating dark signal levels from active and black pixels, leading to image defects due to disparities in dark signal levels between the two types of pixels.
Innovation Solution
The solution involves adjusting the signal gains of active and black pixels by designing different source-follower transistors, such as varying dopant concentrations in semiconductor substrates and wells, to equalize their dark signal levels, ensuring accurate subtraction of dark signals and improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal gains of active and black pixels are not adjusted, then device complexity is reduced, but measurement precision deteriorates due to unequal dark signal levels
Solution Approach 1:
The patent applies local quality by differentiating the signal gain characteristics between active pixels and black pixels. Specifically, black pixels are designed with different source-follower transistor parameters (such as channel width, length, or mobility) to achieve a different gain factor compared to active pixels. This localized differentiation allows each pixel type to have optimized signal characteristics suitable for its function, enabling precise dark signal level matching without requiring complex external adjustment mechanisms.
2Manufacturing precision
If different dopant concentrations are used in substrate and well, then manufacturing precision is improved for gain adjustment, but device complexity increases
Solution Approach 1:
The patent utilizes parameter changes by modifying the physical and electrical characteristics of the source-follower transistors in black pixels. Specifically, it changes parameters such as channel width, length, electron mobility, or dopant concentration to adjust the signal gain. By changing these transistor parameters, the patent achieves precise control over the output signal level of black pixels, enabling them to match the dark signal level of active pixels despite the fundamental difference in their operational characteristics.
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 adjustment enables precise elimination of dark signal levels, enhancing the accuracy of digital image signals and preventing image defects by ensuring that the difference between output voltage signals from active and black pixels accurately represents the light-conversion signal level.
Implementation Method 1
Photoelectric converters of the active pixels generate charge from photoelectric conversion of light
Implementation Method 2
photoelectric converters of the black pixels generate charge from only thermal energy
Data Source
AI summary
An image sensor includes an active pixel and a black pixel. The active pixel has a first signal gain and a first dark signal level, and the black pixel has a second signal gain and a second dark signal level. At least one of the first and second signal gains is adjusted such that the first and second dark signal levels are substantially equal for minimizing image defects in the image sensor.