Dual Conversion Gain Pixel Readout for Dynamic Range
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Solution Overview
Problem
Conventional imaging systems face challenges in capturing images with both bright and dark portions of a scene, as they often result in noisy or over-saturated image signals due to global control signals instructing all pixels to operate in either high or low gain modes, leading to unsightly artifacts in the final image.
Innovation Solution
The implementation of an image sensor pixel array with dual conversion gain capabilities, where pixels can be sequentially operated in high and low conversion gain modes, and readout circuitry that actively selects the appropriate gain setting based on the image signal magnitude, allowing for dynamic adjustment of conversion gain to prevent over-saturation and improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If global control signals are used to instruct all pixels to operate in either high gain mode or low gain mode, then all pixels can be controlled uniformly, but some pixels will generate excessively noisy or over-saturated image signals causing unsightly artifacts
Solution Approach 1:
The patent divides the pixel array into multiple segments or groups, each capable of independent gain mode selection. Row control circuitry is segmented to provide separate control signals to different pixel rows, allowing each segment to operate in the appropriate gain mode (high or low) based on local scene brightness, thereby preventing artifacts while maintaining operational simplicity.
Solution Approach 2:
The patent implements local quality control by allowing different regions of the pixel array to have different gain settings. Each pixel row or column can be independently controlled to operate in high gain mode for dark regions or low gain mode for bright regions, optimizing image signal quality locally rather than applying a uniform global setting.
2Measurement precision
If pixels are controlled to operate in high gain mode for darker scenery, then signal-to-noise ratio improves, but brighter portions become over-saturated
Solution Approach 1:
The patent implements dynamic gain mode switching where pixels can transition between high gain and low gain modes during operation. The row control circuitry dynamically adjusts the gain mode for each pixel row based on real-time scene analysis, allowing pixels in dark regions to use high gain for improved signal-to-noise ratio while pixels in bright regions use low gain to prevent over-saturation, thus maintaining both measurement precision and reliability.
3Reliability
If pixels are controlled to operate in low gain mode for brighter scenery, then over-saturation is prevented, but signal-to-noise ratio deteriorates in dark areas
Solution Approach 1:
The patent applies local quality optimization by enabling different gain modes in different spatial regions of the image sensor. Pixels capturing bright scenery operate in low gain mode to prevent over-saturation and maintain signal accuracy, while pixels capturing dark scenery simultaneously operate in high gain mode to preserve signal-to-noise ratio, with each region's gain mode independently optimized.
4Adaptability or versatility
If sequential high and low conversion gain modes are implemented with readout circuitry selection, then intra-scene dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality in the row control circuitry, which serves dual purposes: it controls the gain mode selection for pixels and also manages the sequential readout of images captured in both high and low conversion gain modes. This universal control mechanism allows the system to achieve extended dynamic range capability without proportionally increasing device complexity, as the same control infrastructure handles multiple functions.
Data Source
AI summary
An imaging system may include image processing circuitry and an image sensor having a pixel, readout circuitry, and control circuitry. The pixel may have a dual conversion gain gate for switching between a high conversion gain mode and a low conversion gain mode. The pixel may capture a first image signal while the dual conversion gain gate is turned of and a second image signal subsequent to capturing the first image signal while the dual conversion gain gate is turned on. The readout circuitry may identify a selected one of the first and second image signals to output to the image processing circuitry based on the first image signal. In this way, the readout circuitry may output a low conversion gain signal when saturating charge is stored on the charge storage region and may output a high conversion gain signal when insufficient charge is stored on the charge storage region.