Reference Pixel Column Readout With Shared Paths for Noise Compensation
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Solution Overview
Problem
Image sensors face a trade-off between noise reduction and active pixel resolution due to the need for additional reference pixels to compensate for fixed pattern noise, which can occupy area that could be used for active pixels, especially in stacked die configurations where increased reference pixels require more inter-die connections and larger readout circuits.
Innovation Solution
Implementing a shared readout path for reference pixel columns to reduce the number of readout paths and circuitry area, while maintaining effective noise compensation by averaging reference signals from multiple reference pixels, thereby minimizing the impact on active pixel resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of reference image sensor pixels is increased to improve noise compensation, then noise compensation improves, but the area available for active image sensor pixels decreases
Solution Approach 1:
Multiple reference pixel columns are merged into a single shared readout path, combining their signals through averaging to improve noise compensation while using minimal area. The readout paths of multiple reference columns are merged at a common node, allowing multiple reference pixels to contribute to noise compensation without requiring separate readout circuitry for each column.
Solution Approach 2:
The shared readout path serves multiple reference pixel columns simultaneously, making the readout circuitry multi-functional. A single readout path handles signals from multiple reference columns, reducing the overall readout circuit area and allowing more space for active pixels while maintaining noise compensation capabilities.
2Reliability
If more reference pixel columns are added to improve noise compensation, then noise compensation improves, but the readout circuit area and complexity increase
Solution Approach 1:
The readout paths of multiple reference pixel columns are merged into a single shared readout path at a common node. This merging reduces the number of separate readout circuits needed, thereby reducing both the area and complexity of the readout circuitry while maintaining the ability to compensate for fixed pattern noise through signal averaging.
Solution Approach 2:
A single readout path is designed to handle signals from multiple reference pixel columns, making it a multi-functional component. This universal readout path reduces the overall complexity by eliminating the need for dedicated readout circuits for each reference column, while still enabling effective noise compensation.
3Reliability
If more reference pixel columns are added in stacked die configuration to improve noise compensation, then noise compensation improves, but the number of inter-die connections increases
Solution Approach 1:
Multiple reference pixel columns are merged into a single shared readout path that requires only one inter-die connection point. By merging the readout paths at a common node within the first die, the patent reduces the number of inter-die connections from multiple separate connections to a single shared connection, thereby reducing the quantity of inter-die connections while maintaining noise compensation.
Data Source
AI summary
An image sensor may include an image sensor pixel array. The image sensor pixel array may include active image sensor pixels that generate image data based on incident light and reference pixels that are optically black for generating reference data for noise compensation. Sets of reference pixels in the same row may be coupled to respective shared readout paths in a source follower binning configuration. The shared readout path may be could to downstream readout circuits. The use of shared readout paths for the reference pixels can reduce the number of reference pixel readout paths. If desired, pixel circuitry may be implemented on a first die, while readout circuitry and at least a portion of the reference pixel readout paths may be implemented on a second die mounted to the first die.