SPAD Control Circuit for Shorter Dead Time and Wider Dynamic Range
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Solution Overview
Problem
Conventional distance measuring systems using Single Photon Avalanche Diodes (SPADs) face difficulties in detecting reflected light received at intervals shorter than the dead time of the SPAD, limiting the dynamic range due to the dead time controlled by the current supplied to the SPAD.
Innovation Solution
A control circuit and distance measuring system that incorporates both passive and active circuits to manage the current supply to the SPAD, allowing for a shorter dead time and thus an enlarged dynamic range by selectively using multiple supply paths to the SPAD element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If current is supplied to SPAD element from single supply path, then circuit complexity is reduced, but dead time cannot be shortened and dynamic range is limited
Solution Approach 1:
The current supply path is segmented into multiple parallel paths (first supply path and second supply path) with different resistance values. The first supply path has higher resistance for normal operation, while the second supply path has lower resistance for rapid recovery. This segmentation allows selective current supply to shorten dead time without excessive complexity.
Solution Approach 2:
The circuit dynamically switches between different supply paths based on operational needs. During normal detection, the first supply path is used. When dead time needs to be shortened (e.g., after detecting reflected light), the second supply path is activated to provide higher current for faster recovery, making the system adaptive to real-time requirements.
2Loss of time
If current is increased to shorten dead time, then dynamic range is enlarged, but uncontrolled avalanche amplification occurs
Solution Approach 1:
The circuit changes the electrical parameter (current magnitude) by switching between supply paths with different resistance values. The first supply path provides current at a level that maintains avalanche control, while the second supply path provides higher current temporarily to shorten dead time. This parameter change is controlled and time-limited, preventing uncontrolled avalanche amplification.
Solution Approach 2:
The high-current second supply path is activated periodically or temporarily only when needed for recovery, not continuously. This periodic activation allows the SPAD element to recover quickly when necessary while maintaining stable operation during normal detection periods, thus controlling avalanche amplification while reducing dead time effects.
3Adaptability or versatility
If multiple supply paths are used to shorten dead time, then dynamic range is enlarged, but circuit complexity increases
Solution Approach 1:
The multiple supply paths serve dual functions: the first supply path handles normal detection operations, while the second supply path handles rapid recovery operations. This multi-functionality allows a single circuit design to adapt to different operational requirements (normal detection vs. quick recovery), enlarging dynamic range without requiring completely separate circuits for each function.
Solution Approach 2:
Different parts of the circuit (different supply paths) have different resistance characteristics tailored to specific functions. The first supply path has higher resistance suitable for stable normal operation, while the second supply path has lower resistance optimized for rapid recovery. This local quality differentiation allows each part to be optimized for its specific purpose, improving overall performance without excessive complexity.
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
The system effectively enlarges the dynamic range of the distance measuring device by shortening the dead time of the SPAD, enabling detection of reflected light at shorter intervals and improving the system's ability to handle varying light levels without saturating.
Implementation Method 1
a signal generated in a Single Photon Avalanche Diode (SPAD) element
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The control circuit according to the present disclosure includes a passive circuit (10) and an active circuit (20). The passive circuit (10) is configured to: supply current to a Single Photon Avalanche Diode (SPAD) element (6a) from a supply path (Rp); and output a first pulse signal (P1) according to a signal generated in the SPAD element (6a). The active circuit (20) is configured to: supply current to the SPAD element (6a) selectively from among a plurality of supply paths; and output a second pulse signal (P2) according to a signal generated in the SPAD element (6a).