Wide Dynamic Range Image Sensor with Charge Overflow Detection
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Solution Overview
Problem
Existing wide dynamic range image sensors face limitations in implementing both dynamic range extension and Integrating While Reading (IWR) methods due to analog data storage on the sense node, which prevents global shutter type functionality.
Innovation Solution
The image sensor incorporates a detection circuit capable of detecting charge overflow at multiple times during the integration phase, storing a signal representative of the time and resetting the photodetector, using transistors and a comparator to manage charge transfer and storage, allowing for both dynamic range extension and IWR methods while maintaining global shutter functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If data representative of integration time are stored in analog fashion on the sense node, then dynamic range extension is achieved, but global shutter functionality and IWR method cannot be implemented
Solution Approach 1:
The patent extracts the data storage function from the sense node by transferring it to a dedicated memory element. The sense node is relieved of its storage burden and used only for charge-to-voltage conversion, while the memory element stores the integration time data in digital form, enabling both global shutter and IWR methods simultaneously.
Solution Approach 2:
The patent introduces a memory element as an intermediary between the sense node and the readout circuitry. This memory element acts as a buffer that stores integration time data in digital form, allowing the sense node to perform its voltage conversion function while the stored data remains preserved and accessible for multiple readout operations.
2Adaptability or versatility
If pixel saturation limit is increased to extend dynamic range, then higher luminosity acceptance is achieved, but pixel structure complexity increases
Solution Approach 1:
The patent segments the pixel into distinct functional blocks: a photodetector for charge collection, a sense node for voltage conversion, a memory element for data storage, and a readout circuit for signal processing. This segmentation allows each component to be optimized independently, extending dynamic range without proportionally increasing overall pixel complexity.
Solution Approach 2:
The patent creates a multi-functional pixel structure where the sense node serves both as a charge-to-voltage converter and as part of the readout mechanism, while the memory element provides both integration time storage and enables global shutter functionality. This multi-functionality extends the luminosity acceptance range without linearly increasing structural complexity.
3Productivity
If IWR method is implemented to increase frame rate, then image acquisition speed is improved, but analog storage on sense node prevents simultaneous readout
Solution Approach 1:
The patent extracts the data storage function from the sense node and places it in a dedicated memory element. This allows the sense node to be used for reliable voltage conversion during each frame while the memory element preserves previous frame data, enabling true IWR operation where readout of previous frames occurs simultaneously with integration of current frames.
Solution Approach 2:
The patent enables continuous operation by allowing the readout circuit to continuously read from the memory element while the photodetector continuously integrates new charges. The memory element ensures that readout operations for previous frames do not interrupt the integration process of current frames, maintaining continuous useful action and high frame rates.
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 enhances the dynamic range of the image sensor, enabling efficient IWR and global shutter capabilities with reduced noise levels, significantly increasing the number of images acquired per second and improving signal-to-noise ratio.
Implementation Method 1
a photodetector and a circuit for reading out the quantity of charges collected by the photodetector at the end of a phase of charge collection by the photodetector
Data Source
AI summary
An image sensor including pixels, each pixel including a photodetector and a circuit for reading out the quantity of charges collected by the photodetector at the end of a phase of charge collection by the photodetector. The image sensor further includes, for at least one of the pixels, a detection circuit capable, at least at two different times during the phase, of detecting whether the quantity of charges collected at the time by the photodetector of the pixel exceeds a threshold and, in the case where the quantity of charges collected at the time exceeds the threshold, of storing a first signal representative of the time and of resetting the photodetector.