Single Photon Counting Apparatus Using PLL Edge Combiner and Dual Tree Sampling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Single Photon Avalanche Diodes (SPADs) face challenges in accurately detecting fluorescence photons due to ambient light and heat interference, and in Time of Flight applications, pile-up distortion occurs when photons activated later in a cycle are not detected, leading to inaccurate counting of single photons.
Innovation Solution
An apparatus and method utilizing an edge combiner with Phase-Locked Loops (PLL) to generate a combined signal, sampling units with both OR and XOR trees, and a calculation unit with a histogramming Time to Digital Converter (TDC) to accurately count single photons, while compensating for propagation delay using a Delay-Locked Loop (DLL).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an SPAD is used to increase sensitivity in fluorescence applications, then detection sensitivity is improved, but ambient light and heat activate the SPAD causing false detection of fluorescence photons
Solution Approach 1:
The patent applies preliminary action by using a start signal to pre-activate the SPAD before the actual fluorescence photons arrive. This allows the system to distinguish between photons arriving during the expected fluorescence window versus those caused by ambient light or heat, enabling accurate photon counting despite the high sensitivity that normally causes false detections
Solution Approach 2:
The patent implements periodic action through time-gated detection where the SPAD is activated in periodic cycles synchronized with the excitation light source. By opening the detection window only during expected fluorescence emission periods and keeping it closed during other times, the system eliminates ambient light and heat interference while maintaining high detection sensitivity for actual fluorescence photons
2Measurement precision
If an SPAD is used to increase sensitivity in Time of Flight applications, then detection sensitivity is improved, but photons activated second or later are not detected causing pile-up distortion
Solution Approach 1:
The patent applies dynamics by implementing a re-arming mechanism that dynamically resets the SPAD detection window based on the arrival time of detected photons. When a photon is detected, the system calculates its time of flight and dynamically adjusts the next detection window to ensure no photons are missed, preventing pile-up distortion while maintaining high detection sensitivity
Solution Approach 2:
The patent uses feedback by continuously monitoring detected photon times and using this information to adjust subsequent detection windows. The system measures the time difference between consecutive photons and dynamically re-arms the SPAD to detect subsequent photons within their expected arrival windows, eliminating pile-up distortion while preserving detection sensitivity
3Device complexity
If sampling is performed using only an OR tree or only an XOR tree, then device complexity is reduced, but event sampling accuracy decreases leading to photon counting errors
Solution Approach 1:
The patent merges two complementary sampling approaches by combining both OR tree and XOR tree sampling circuits. The OR tree samples all events including coincident ones, while the XOR tree samples only non-coincident events. By merging these two sampling streams and combining their results, the system achieves complete and accurate event sampling without losing any photons, thereby improving measurement precision while accepting increased device 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
This solution enables accurate counting of single photons by minimizing event omission and propagation delay, improving detection sensitivity and reducing power consumption, suitable for applications like Time Correlated Single Photon Counting (TCSPC) and Fluorescence Lifetime Imaging Microscopy (FLIM).
Implementation Method 1
an edge combiner configured to detect an edge of each of applied clocks using a plurality of Phase-Locked Loops (PLL) to generate a combined signal
Implementation Method 2
A compensation unit for compensating propagation delay between the OR tree and the XOR tree using a Delay-Locked Loop (DLL)
Implementation Method 3
an apparatus for counting single photons generated by a Single Photon Avalanche Diode (SPAD)
Data Source
AI summary
Disclosed is an apparatus for counting single photons including an edge combiner configured to detect an edge of each of applied clocks using a plurality of Phase-Locked Loops (PLL) to generate a combined signal; a sampling unit configured to sample all events occurring in each SPAD of a single photon detection diode (SPAD) array using an OR tree and an XOR tree; and a calculation unit configured to count the sampled events based on the combined signal to count single photons.