Single Photodiode Pixel Circuit for Asynchronous Image Acquisition
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Solution Overview
Problem
Conventional image sensors face limitations in temporal and spatial resolution due to frame-based acquisition, leading to high redundancy in data, increased complexity and cost, and reduced dynamic range, which is exacerbated by the use of two separate photodiodes for change detection and exposure measurement.
Innovation Solution
A pixel circuit utilizing a single photodiode for both change detection and exposure measurement, with an integrated transient detector and exposure measurement circuit, allowing for asynchronous data acquisition and reducing spatial divergence, thereby improving resolution and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two separate photodiodes are used for change detection and exposure measurement, then measurement precision is improved, but device complexity and area increase
Solution Approach 1:
The patent merges the change detection function and exposure measurement function into a single photodiode, eliminating the need for two separate photodiodes. This consolidation reduces device complexity and area while maintaining measurement precision through integrated circuitry that processes both functions sequentially within the same photodetector element.
Solution Approach 2:
The single photodiode is designed to perform multiple functions: both change detection (transient detection) and exposure measurement (intensity integration). The photodiode serves as a universal sensor element that can operate in different modes depending on the operational phase, reducing the total number of components required.
2Measurement precision
If two separate photodiodes are used for change detection and exposure measurement, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
By combining the functions of two separate photodiodes into one, the patent reduces the number of fabrication steps, alignment requirements, and component interconnections needed during manufacturing. This simplification directly lowers manufacturing cost while maintaining the dual functionality required for precise measurement.
3Measurement precision
If frame-based acquisition is used, then temporal resolution is improved, but data redundancy increases
Solution Approach 1:
The patent implements dynamic, event-driven acquisition where the sensor continuously monitors for changes and only records data when actual scene changes occur. This dynamic operation mode allows for high temporal resolution by capturing changes as they happen, while simultaneously reducing data redundancy by not recording redundant unchanged frames.
Solution Approach 2:
The pixel circuit autonomously detects changes in the optical scene and triggers exposure measurements only when necessary, without requiring external frame timing signals. This self-service capability enables the sensor to adapt its operation to actual scene dynamics, achieving high temporal resolution while minimizing redundant data generation.
4Measurement precision
If external timing signals are used for frame-based acquisition, then temporal resolution is improved, but spatial divergence increases
Solution Approach 1:
The pixel circuit uses its own internally generated timing signals for sequential operations (reset, integration, readout) rather than relying on external frame timing signals. This self-service approach eliminates spatial divergence caused by external signal distribution while maintaining precise temporal control through integrated circuit timing.
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 enables continuous, high-resolution acquisition of dynamic scene information with reduced data volume, minimizing temporal redundancy and enhancing imaging quality by eliminating the need for external timing signals and using a single photodiode per pixel, resulting in smaller sensor chip dimensions and faster measurement processes.
Implementation Method 1
a front-end circuit (1) comprising a single photodiode (PD) and having an output (4), said front-end circuit (1) being configured for delivering on said output (4) a photoreceptor signal derived from a light exposure of said single photodiode (PD)
Data Source
AI summary
The invention relates to pixel circuit and an operating method thereof, comprising—a front-end circuit (1) comprising a single photodiode (PD) and having an output (4), said front-end circuit (1) being configured for delivering on said output a photoreceptor signal derived from a light exposure of said single photodiode (PD);—a transient detector circuit (2) configured for detecting a change in said photoreceptor signal delivered on said output (4);—an exposure measurement circuit (3) configured for measuring said photoreceptor signal delivered on said output (4) upon detection by the transient detector circuit (2) of a change in the photoreceptor signal. The invention also relates to an image sensor comprising a plurality of pixel circuits