Delta Image Sensor With External Pixel Storage for Event Detection
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Solution Overview
Problem
Current image sensors face limitations in efficiently processing and storing illumination data within pixels, leading to issues such as gradual storage degradation, sensitivity to mismatches, and reduced flexibility in light-to-electric conversion, especially in dynamic vision applications where event-based processing is crucial.
Innovation Solution
A delta image sensor design that combines digital conversion and storage within pixel circuits, enabling local evaluation of illumination level changes and event information preparation, with features like external digital storage and comparison circuits to detect changes, and shared circuitry between pixels for efficient resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital conversion and storage are implemented within each pixel circuit, then measurement precision and event detection accuracy are improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The pixel array is divided into multiple blocks, with each block containing a subset of pixels that share common circuitry (ADC, digital storage, comparison circuits). This segmentation allows digital processing capabilities to be distributed across blocks rather than requiring full digital circuits in every pixel, reducing individual pixel complexity while maintaining event detection accuracy through local digital processing.
Solution Approach 2:
The patent transitions from traditional analogue in-pixel processing to digital processing by adding a digital dimension to the pixel circuit. Digital storage circuits and comparison circuits are integrated alongside the photosensor and ADC, enabling digital event detection. This dimensional transition from analogue to digital processing improves measurement precision while the shared circuitry approach manages the resulting complexity.
2Device complexity
If shared circuitry is implemented between pixels, then device complexity is reduced and manufacturing cost decreases, but productivity and processing speed may be limited
Solution Approach 1:
Analogue-to-digital conversion is performed preliminarily within each pixel circuit before the digital signal is shared across the block. This preliminary ADC conversion ensures that each pixel has its signal ready in digital form, enabling fast parallel comparison operations across multiple pixels using shared comparison circuits, thus maintaining high processing speed while reducing overall circuitry complexity.
Solution Approach 2:
Multiple pixels within a block share common digital storage circuits, comparison circuits, and output logic. This merging of resources reduces the total number of circuits needed compared to fully independent pixel circuits, lowering device complexity and manufacturing cost. The shared circuits process digital signals from multiple pixels in parallel, maintaining high productivity.
3Device complexity
If analogue storage is used in dynamic vision sensors, then device complexity is reduced, but reliability deteriorates due to storage degradation and hot-pixel issues
Solution Approach 1:
The patent replaces analogue storage mechanisms with digital storage circuits within the pixel array. Instead of relying on analogue capacitor storage that degrades over time and is sensitive to hot-pixel effects, the invention uses digital storage elements (such as flip-flops or registers) that maintain stable binary states. This substitution of digital for analogue storage significantly improves reliability and storage stability while keeping device complexity manageable through the shared circuitry architecture.
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 an area-optimized, high-resolution, and cost-effective sensor that efficiently processes and stores illumination data, reducing power consumption and improving event detection accuracy, while allowing for flexible light source modulation and suppression of unwanted signals.
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 a plurality of acquisition circuits corresponding to at least one pixel. Each acquisition circuit includes at least one sensor circuit comprising a photosensor to generate a sensor signal, VSIG, depending on a light signal; 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; at least one digital comparison circuit to compare the level of the stored representation with the current VSIG to detect whether a changed level is present; and at least one digital output circuit configured to generate an event output under the condition of the changed level. A digital representation may be externally written to the digital storage circuit of the at least one pixel.