SPAD Optical Sensor Pulse Width Detection Circuit
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Solution Overview
Problem
Conventional Single Photon Avalanche Diode (SPAD) elements suffer from long deadtime and low dynamic range under strong ambient light, leading to issues like multi-triggering and SPAD latching, which impede their ability to detect incident photons and generate corresponding sensing signals effectively.
Innovation Solution
An optical sensing device is developed, featuring a detection circuit that monitors the pulse width of sensing signals from the SPAD element and generates a reset signal when the pulse width exceeds a threshold. This reset signal initiates another quenching and recharging cycle, preventing SPAD latching and improving the dynamic range and photon count rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the recharging current is increased to shorten recharging time, then the dead time is reduced, but the SPAD element may latch and become unable to return to its original state
Solution Approach 1:
The detection circuit monitors the voltage level of the SPAD element in real-time during the recharging process. When the voltage reaches a predetermined threshold indicating successful recharging, the circuit automatically stops the recharging current, preventing over-charging and latching effects while ensuring the SPAD element is fully recharged to minimize dead time.
Solution Approach 2:
The SPAD element itself provides the feedback signal through its voltage level changes during recharging. The element's inherent electrical characteristics are used to indicate when it has been sufficiently recharged, eliminating the need for external monitoring components and enabling automatic control of the recharging process.
2Reliability
If the holding time is extended to prevent multi-triggering, then the dynamic range is improved, but the photon count rate decreases
Solution Approach 1:
The holding time is made dynamic rather than fixed. The detection circuit continuously monitors the SPAD element's voltage level and adjusts the holding time based on the actual recharging status. This allows the system to use shorter holding times when the SPAD recovers quickly (maintaining high count rate) and longer holding times when needed to prevent multi-triggering (maintaining dynamic range).
Solution Approach 2:
The system changes the holding time parameter dynamically based on operating conditions. By monitoring the voltage recovery characteristics of the SPAD element, the circuit adjusts the holding time to optimize the balance between preventing multi-triggering and maintaining high photon count rate, rather than using a conservative fixed holding time that limits performance.
3Loss of time
If the quenching current is increased to quickly return the SPAD to its original state, then the dead time is reduced, but the risk of latching effect increases
Solution Approach 1:
The detection circuit is prepared in advance to monitor the SPAD element's voltage level during quenching. When the voltage reaches the threshold indicating successful quenching, the circuit immediately stops the quenching current, preventing excessive current that could cause latching. This preliminary monitoring setup enables precise control of the quenching process.
Solution Approach 2:
The quenching process is executed rapidly with real-time monitoring. The high quenching current is applied briefly to quickly return the SPAD to its original state, and the detection circuit immediately detects when quenching is complete and stops the current, skipping any unnecessary extended quenching that would increase latching risk while ensuring complete quenching.
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 proposed solution effectively addresses the problems of long deadtime, low dynamic range, and multi-triggering in SPAD elements under strong ambient light, enhancing their ability to detect incident photons and improve sensing performance.
Implementation Method 1
Distance measurement may be realized by optical sensing elements, which utilize optoelectronic conversion to convert the received optical signals into electrical signals
Implementation Method 2
One of the optical sensing elements commonly used in the industry is the Single Photon Avalanche Diode (SPAD) element which is an optical detector with high sensitivity and able to detect a single photon
Data Source
AI summary
An optical sensing device is provided. The optical sensing device includes an optical sensing element and a detection circuit. The optical sensing element senses an incident photon and generates a sensing signal. The detection circuit detects a pulse width of the sensing signal, and generates a reset signal when the pulse width is larger than a threshold value. Thereby, the optical sensing device is reset according to the reset signal and a dynamic range of the optical sensing device under strong ambient light will be further improved.