Pinned-Photodiode Image Sensor Shared Amplifier Readout
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Solution Overview
Problem
Existing RGB solid state image sensors, particularly those using the Bayer pattern, face challenges in reducing the sensitivity difference between green and red/blue pixels due to varying color filter absorption coefficients, which affects exposure and gain adjustments.
Innovation Solution
The implementation of a solid state image sensor with a shared output amplifier across adjacent rows in each column, utilizing a cyclical arrangement of transfer gate control lines to alternate the readout sequence, allowing for independent exposure and gain adjustments of green and red/blue pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Bayer pattern with RGB color filters is used, then color image capture is achieved, but green pixels have higher sensitivity than red and blue pixels due to different absorption coefficients
Solution Approach 1:
The patent segments the readout process by row pairs, allowing independent control of green and red/blue pixel readout sequences. Transfer gate control lines are assigned to specific row pairs, enabling separate exposure and gain adjustments for green pixels versus red/blue pixels, thereby resolving the sensitivity uniformity issue while maintaining operational simplicity
Solution Approach 2:
The patent introduces dynamic control through transfer gate control lines that can be independently configured for different row pairs. This dynamic readout control allows the system to adapt exposure and gain settings in real-time for different color channels, solving the contradiction between measurement precision and ease of operation
2Device complexity
If multiple pixels share a common output amplifier, then device complexity is reduced, but mismatches in gain and offset between green and red/blue pixels cannot be eliminated
Solution Approach 1:
The patent segments the pixel array into distinct row pairs, each with dedicated transfer gate control lines. This segmentation allows green pixels and red/blue pixels to be read out through separate control paths sharing the common amplifier, enabling independent gain and offset calibration for each color channel while maintaining amplifier sharing benefits
Solution Approach 2:
The transfer gate control lines act as intermediaries between the pixel rows and the common output amplifier. By controlling which row pair is active at any given time, these intermediaries enable separate signal paths for green and red/blue pixels, allowing gain and offset mismatches to be eliminated while still using a shared amplifier
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 enables optimized dynamic range, signal-to-noise ratio, and reduced dark current by allowing for differential exposure and gain settings, as well as eliminating mismatches in gain and offset between green and red/blue pixels, thereby improving image quality.
Implementation Method 1
Each pixel comprises a photodiode
Data Source
AI summary
A pinned-photodiode image sensor using shared output amplifiers, for example output amplifiers in the 2.5T arrangement has transfer gate control lines alternating or cross-coupled between successive columns or adjacent rows. This assists in removing row-row mismatches. In preferred embodiments, the approach is applied to Bayer pattern RGB sensors, and allows the gain and/or the exposure of green pixels to be controlled separately from those of red and blue pixels.