Delta Image Sensor with Digital Pixel Storage for Stable Event Detection
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Solution Overview
Problem
Existing image sensors face challenges with analogue storage methods, which suffer from gradual storage degradation, sensitivity to mismatch, and reduced flexibility in light-to-electric conversion, particularly in dynamic vision sensors where event-based processing is critical.
Innovation Solution
A delta image sensor with digital pixel storage and synchronized sampling, utilizing a single-slope analogue-to-digital conversion circuit to store and compare previous illumination levels, generating event outputs based on changes, and optimizing repeat rates for light source modulation to suppress or enhance responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analogue storage is used in dynamic vision sensors, then the device complexity is reduced, but storage degradation and sensitivity to mismatch occur
Solution Approach 1:
The patent replaces the mechanical/physical analogue storage system with a digital storage system. Specifically, the previous illumination level is converted to digital form via ADC and stored in a digital storage circuit, eliminating the gradual degradation inherent in analogue storage while maintaining the event-based processing architecture.
Solution Approach 2:
The patent changes the storage parameter from analogue voltage levels to digital values. By storing the digital representation of the previous illumination level rather than the analogue signal itself, the system achieves stable, non-degrading storage while reducing sensitivity to analogue mismatch errors.
2Measurement precision
If digital storage is used in pixels, then storage fidelity is improved, but area usage increases
Solution Approach 1:
The patent uses a single-slope ADC that performs only partial conversion - it converts the analogue signal to digital form just enough to capture the necessary illumination level information, then stores only this digital value in a compact digital storage circuit within each pixel, achieving high fidelity without requiring full high-resolution conversion.
Solution Approach 2:
The patent segments the pixel circuit into distinct functional blocks: photosensor, single-slope ADC, digital storage circuit, and event generation logic. This segmentation allows each component to be optimized independently, with the digital storage circuit being compact and efficient while maintaining overall pixel functionality.
3Productivity
If repeat rate is synchronized with light source modulation, then redundant event generation is reduced, but response to modulation may be suppressed
Solution Approach 1:
The patent implements periodic sampling at a repeat rate that is synchronized with the light source modulation frequency. By sampling at this specific periodic rate, the system captures the illumination level at consistent phases of the modulation cycle, reducing redundant event generation while maintaining accurate detection of actual scene changes through the event generation logic that compares current and previous digital values.
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 results in a high-resolution, cost-optimized image sensor with improved fidelity and efficiency in power and area usage, reducing redundant event generation and maintaining information content while minimizing data volume.
Implementation Method 1
a photosensor configured to generate a sensor signal, VSIG, depending on a light signal illuminating the photosensor
Data Source
AI summary
A delta image sensor comprising an arrangement of pixels and acquisition circuits corresponding to at least one pixel. Each acquisition circuit includes a sensor circuit comprising a photosensor to generate a sensor signal, VSIG, depending on a light signal illuminating the photosensor; at least one analogue to digital conversion, A/D, circuit configured to convert a current VSIG to a digital signal; at least one digital storage circuit configured to store a representation of at least one digital signal corresponding to a previous VSIG; a digital comparison circuit configured to compare the level of the stored representation with the current VSIG to detect whether a changed level is present; and a digital output circuit configured to generate an event output when the level has changed. The repeat rate of the analogue to digital conversion is chosen from one or more repeat rates corresponding to modulation of the light signal.