Per-Column Image Sensor Gain Control 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 require all pixels in a row to operate in either high or low gain modes, leading to noisy or over-saturated image signals and unsightly artifacts.
Innovation Solution
Implementing per-column control and readout circuits that allow for independent gain adjustments of each pixel column, using dual conversion gain control signals to adjust the conversion gain of each pixel based on the captured image signals, enabling pixels to operate in either high or low gain modes as needed to prevent saturation and improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If all pixels in a row operate in the same gain mode (high or low), then the control circuitry is simple, but pixels capturing brighter scenes become over-saturated while pixels capturing darker scenes become noisy
Solution Approach 1:
The patent divides the pixel array into multiple columns, each with its own independent control circuitry. This segmentation allows different columns to operate in different gain modes simultaneously, resolving the contradiction by enabling per-column gain control without requiring per-pixel independent control, thus balancing circuit complexity with image signal quality.
Solution Approach 2:
The patent implements local quality control by allowing each column to have its own gain control mechanism. This enables different regions (columns) of the pixel array to operate with different gain settings optimized for their specific brightness conditions, improving image signal quality while maintaining manageable circuit complexity through column-level rather than pixel-level control.
2Reliability
If per-pixel gain adjustment is implemented, then image signal quality is improved, but device complexity increases significantly
Solution Approach 1:
The patent segments the gain control function at the column level rather than implementing full per-pixel control. Each column has its own control circuitry that can independently adjust gain, achieving improved image signal quality while reducing device complexity compared to pixel-level control.
Solution Approach 2:
The patent merges multiple pixels into column-based control units. By combining control functions at the column level, the system achieves per-column gain adjustment without the full complexity of per-pixel control, effectively merging the control responsibilities for multiple pixels into single column-level circuits.
3Measurement precision
If high gain mode is used for darker scenes, then signal-to-noise ratio improves, but brighter portions of the scene become over-saturated
Solution Approach 1:
The patent segments the pixel array into columns with independent gain control. This allows darker columns to use high gain mode for improved signal-to-noise ratio while brighter columns use low gain mode to prevent over-saturation, simultaneously addressing both measurement precision and harmful over-saturation artifacts.
Solution Approach 2:
The patent applies local quality control by enabling different gain settings for different columns based on their specific brightness conditions. This ensures that each column operates with the optimal gain mode for its content, improving signal-to-noise ratio in dark regions while preventing over-saturation in bright regions.
Data Source
AI summary
An imaging system may include an array of image pixels arranged in rows and columns that includes first and second pixels in two different columns and a common row. A first column readout circuit may control the first pixel to exhibit a first gain and a second column readout circuit may control the second pixel to exhibit a second gain. The first and second readout circuits may determine whether to adjust the gain of the first and second pixels based on image signals that are captured by the first and second pixels. For example, the first readout circuit may selectively activate a dual conversion gain transistor in the first pixel based on an image signal received from the first pixel and the second readout circuit may independently and selectively activate a dual conversion gain transistor in the second pixel based on an image signal received from the second pixel.