Dual-Photodiode Pixel Circuit for LED Flickering Detection
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Solution Overview
Problem
Image sensing devices face challenges in detecting LED signals under strong light environments, as the exposure time needed to detect LEDs effectively conflicts with maintaining dynamic range, especially when LEDs flicker at high frequencies.
Innovation Solution
The implementation of an image sensing device with multiple pixel circuits, each comprising a first and second sensing circuit, where the first sensing circuit operates with an exposure time longer than the flickering cycle to obtain a baseline result, and the second sensing circuit operates simultaneously with a shorter exposure time to enhance detection accuracy, allowing for simultaneous LED detection without sacrificing dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exposure time is extended to detect LED signals under strong light, then LED detection capability is improved, but dynamic range is reduced
Solution Approach 1:
The pixel circuit is divided into two independent sensing circuits: a first sensing circuit with a first photodiode for long exposure time detection, and a second sensing circuit with a second photodiode for short exposure time detection. This segmentation allows each circuit to specialize in different exposure requirements, enabling LED detection without compromising dynamic range.
Solution Approach 2:
The system dynamically selects between different exposure times based on detection needs. The control circuit can switch between using the first sensing circuit for LED detection (when long exposure is needed) and the second sensing circuit for general imaging (when dynamic range is prioritized), making the exposure time adaptive to the scene requirements.
2Reliability
If the exposure time is shortened to maintain dynamic range under strong light, then dynamic range is preserved, but LED detection capability is lost
Solution Approach 1:
The pixel circuit is divided into two independent sensing circuits: a first sensing circuit with a first photodiode for long exposure time detection, and a second sensing circuit with a second photodiode for short exposure time detection. This segmentation allows each circuit to specialize in different exposure requirements, enabling LED detection without compromising dynamic range.
Solution Approach 2:
Each pixel circuit contains both sensing circuits, making the pixel multi-functional. The first photodiode can be used when LED detection is needed, while the second photodiode handles general imaging requirements, allowing the same pixel to serve multiple purposes based on the scene.
3Measurement precision
If multiple sensing circuits with different exposure times are used, then LED detection accuracy is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is divided into two independent sensing circuits: a first sensing circuit with a first photodiode for long exposure time detection, and a second sensing circuit with a second photodiode for short exposure time detection. This segmentation allows each circuit to specialize in different exposure requirements, enabling LED detection without compromising dynamic range.
Solution Approach 2:
Both sensing circuits share common components including the transfer transistor, storage node, and readout circuitry. This merging of shared resources reduces the overall complexity increase that would otherwise result from having completely separate circuits, as the dual-photodiode structure reuses existing circuit elements.
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 method maintains LED detection capability under strong light conditions while preventing a reduction in dynamic range, effectively determining LED flickering by combining results from both sensing circuits.
Implementation Method 1
sensing light by the first sensing circuit with a first exposure time longer than the flickering cycle time, thereby obtaining a first sensing result; sensing light, simultaneously by the first sensing circuit and the second sensing circuit with a second exposure time shorter than the flickering cycle time
Data Source
AI summary
An operating method of an image sensing device capable of detecting several light emitting diodes each having a flickering cycle time, the image sensing device includes several pixel circuits, each of the several pixel circuits includes a first sensing circuit and a second sensing circuit, the operating method including the following operations: operating the image sensing device in a first operating mode, including: sensing light by the first sensing circuit with a first exposure time longer than the flickering cycle time, thereby obtaining a first sensing result; sensing light, simultaneously by the first sensing circuit and the second sensing circuit with a second exposure time shorter than the flickering cycle time, thereby obtaining a second sensing result and a third sensing result; determining whether there is LED (light emitting diode) flickering or not according to the first sensing result, the second sensing result and the third sensing result.