Skip Mode Image Sensor Dynamic Range Extension
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Solution Overview
Problem
Conventional CMOS image sensors have a limited dynamic range, typically around 70 dB, which prevents them from capturing detailed images across a wide range of illuminations from dark to bright, and they also waste resources during skip mode operations by leaving readout circuitry unused.
Innovation Solution
Implementing a skip mode operation with multiple integration periods, where unused column readout circuits are utilized to read out charge collected during additional integration times, effectively increasing the dynamic range and reducing processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CMOS image sensors are used with standard readout operation, then the full well capacity determines the dynamic range, but the dynamic range is limited to around 70 dB which is insufficient for capturing both shadow and highlight details
Solution Approach 1:
The pixel array is divided into two groups: first pixels that are reset after a first integration time to capture highlight details, and second pixels that continue integrating to capture shadow details. This segmentation allows simultaneous capture of different exposure levels, effectively extending the dynamic range from 70 dB to over 110 dB and enabling coverage of the full illumination range from dark shadows to bright highlights.
Solution Approach 2:
The first pixels are reset at a predetermined time during the integration period to capture the highlight information before the second pixels complete their full integration. This preliminary action of resetting certain pixels allows the system to capture both the early (highlight) and late (shadow) integration results, achieving wide dynamic range capability.
2Productivity
If skip mode is used to reduce readout time, then processing speed increases, but a substantial part of the column readout circuit remains unused (half for 2× skip, three-fourths for 4× skip)
Solution Approach 1:
The column readout circuits are designed to serve multiple functions: during normal operation they read out all pixels, and during skip mode they read out both the first pixels (from skipped columns) and second pixels (from active columns). This multi-functionality ensures that no readout circuit remains unused during skip mode, maintaining full utilization while achieving faster readout speeds and reduced processing time.
Solution Approach 2:
The system dynamically switches between different readout modes (full readout, 2× skip mode, 4× skip mode) by controlling which pixels are reset and when, allowing the readout circuits to adapt their operation to match the desired speed-performance tradeoff while maintaining full circuit utilization in each mode.
3Measurement precision
If the first pixels are reset after a first integration time to capture highlight details, then the dynamic range is extended, but the readout circuitry must handle additional signals increasing complexity
Solution Approach 1:
The readout circuits merge the readout of first pixels and second pixels through a unified signal path. The first pixel signals and second pixel signals are combined and processed together in the same column readout circuits, eliminating the need for separate readout paths and minimizing the increase in circuit complexity while achieving extended dynamic range.
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 enhances the dynamic range of image sensors to at least 110 dB, allowing for better capture of both shadow and highlight details while optimizing processing efficiency.
Implementation Method 1
A pixel's photosensor collects photons (incoming light) and converts the photons into an electrical charge
Data Source
AI summary
Methods, apparatuses and systems provide a high dynamic range mode of operation for an image sensor when operating in a skip mode where certain pixels of an array are not readout. Multiple integration periods are employed in the skip mode with selected pixels being readout through circuits associated with pixels that are not readout.