Imaging Sensor Overflow Unit Dynamic Range
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Solution Overview
Problem
Conventional active pixel sensors (APS) have a limited dynamic range due to voltage swing constraints and intrinsic noise, which is insufficient for applications requiring wider ranges, such as medical imaging and automotive imaging in varying light conditions.
Innovation Solution
The introduction of an array of pixels with a first overflow unit comprising a transistor and capacitance, allowing overflow charge to be stored and controlled, and further overflow units in series to increase dynamic range, with adaptive gain and noise management during readout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional APS sensors are used, then the device complexity is low, but the dynamic range is limited
Solution Approach 1:
The pixel is divided into multiple independent photodiodes (first photodiode, second photodiode, third photodiode) that can be selectively activated. This segmentation allows the sensor to handle different light intensity levels across multiple channels, effectively extending the dynamic range without requiring a complete redesign of the entire sensor architecture.
Solution Approach 2:
The invention introduces dynamic control mechanisms including selectable gain stages (first gain, second gain) and programmable exposure time (integration period). The sensor can dynamically adjust which photodiodes are active, the gain applied to each channel, and the integration period length, allowing adaptive optimization for varying scene conditions and effectively expanding the usable dynamic range.
2Reliability
If the integration period is extended to capture more charge, then the dynamic range increases, but the noise from intrinsic sensor limitations worsens
Solution Approach 1:
The invention uses multiple photodiodes with different capacitances and gain stages to capture charge at different levels. Rather than attempting to capture all charge in a single channel, the system takes partial measurements from multiple channels (first photodiode for low light, second photodiode for medium light, third photodiode for high light) and combines them, effectively extending the linear range while managing noise through appropriate channel selection.
Solution Approach 2:
The system dynamically changes key parameters including the integration period duration, the selected photodiode channel, and the gain applied to each channel. By programmatically adjusting these parameters based on scene analysis, the sensor can optimize the signal-to-noise ratio for different lighting conditions, capturing maximum useful charge while minimizing the impact of intrinsic noise.
3Reliability
If multiple photodiodes and overflow units are added to increase charge storage capacity, then the dynamic range expands, but the device complexity increases
Solution Approach 1:
The invention designs a multi-purpose pixel structure where shared circuitry (readout circuit, gain stages, control logic) serves multiple photodiodes. The overflow unit and transfer mechanisms are designed to handle charge from any active photodiode, creating a universal charge handling system that manages complexity through functional consolidation rather than dedicated separate paths for each photodiode.
Solution Approach 2:
The patent implements a hierarchical charge storage and transfer architecture where charge from photodiodes is transferred to overflow units, which can then be transferred to additional storage capacitances. This nested structure (photodiode → overflow unit → additional storage) allows progressive charge storage with controlled complexity, where each nesting level is only activated when the previous level is saturated.
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 solution significantly enhances the dynamic range of each pixel, enabling the storage of more charge while minimizing noise, thus meeting the requirements of applications needing wider dynamic ranges.
Implementation Method 1
a photodiode PD; a node arranged to develop or accumulate a voltage based on charge accumulated at the photodiode due to photogeneration
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
A sensor array comprising an array of pixels and a method of operating the same are disclosed. Each pixel of the sensor array comprises: a photodiode; a node arranged to develop a voltage based on charge accumulated at the photodiode due to photogeneration; and a first overflow unit coupled to the node. The first overflow unit comprises a transistor and a capacitance. The sensor array is arranged to control the first overflow unit to accept overflow charge from the node into the capacitance of that overflow unit, and to subsequently read the overflow charge stored at the capacitance. Each pixel may comprise one or more further overflow units in series with the first overflow unit. The overflow units provide the sensor array with enhanced dynamic range. Also disclosed is a single pixel sensor with enhanced dynamic range.