Mixed Digital-Analog Photon Detection System for Coincidence Events
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Solution Overview
Problem
Existing photon detection systems, such as SPAD and SiPM arrays, face challenges in detecting single photon events and time coincidence events while maintaining spatial resolution, scalability, and minimizing noise and resource bottlenecks.
Innovation Solution
A mixed digital-analog system with event-driven readout that includes digital-to-analog transducers, an analog adder node, and comparators to detect single photon events and time coincidence events on-chip, preserving spatial information and optimizing computational resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPAD arrays with complete digital processing are used, then spatial resolution and noise immunity are improved, but the ability to detect time coincidence events is lost
Solution Approach 1:
The patent combines digital and analog processing domains by integrating an analog adder node that receives signals from multiple SPAD pixels and sums them analogously, then compares the summed signal against threshold values to detect time coincidence events. This merging allows the system to maintain the noise immunity and spatial resolution of digital SPAD arrays while adding time coincidence detection capability through analog signal processing.
2Adaptability or versatility
If timing electronics are integrated in each pixel to detect time coincidence events, then time coincidence detection capability is improved, but device complexity and fill-factor are worsened
Solution Approach 1:
The patent segments the time coincidence detection function from individual pixels and relocates it to a separate analog processing stage. Instead of each pixel containing complete timing electronics, the system divides the detection process into: (1) individual pixel photon detection with simple timing, and (2) centralized analog summation and threshold comparison. This segmentation reduces per-pixel complexity while maintaining overall detection capability.
Solution Approach 2:
The patent introduces an analog adder node as an intermediary component between the digital pixel outputs and the final coincidence detection logic. This intermediary converts multiple digital pixel signals into a single analog summed signal, which is then thresholded to detect time coincidence events. The intermediary simplifies the overall system architecture by centralizing the complex timing analysis function.
3Device complexity
If fixed-frequency frame acquisition is used, then system simplicity is improved, but data transmission and processing overhead increase
Solution Approach 1:
The patent replaces continuous fixed-frequency frame acquisition with event-driven periodic action. The system activates pixel readout and data transmission only when photons are detected or when time coincidence events occur, rather than continuously acquiring frames at a fixed rate. This event-triggered periodic action reduces unnecessary data transmission and processing, lowering power consumption while maintaining system simplicity.
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 detects single photon events and time coincidence events with noise immunity, reduces data transmission and processing bottlenecks, and ensures spatial resolution, while being scalable and modular.
Implementation Method 1
When a photon strikes on the SPAD, an electron-lacuna pair is generated, which triggers an avalanche process of multiplication of the electric charges
Implementation Method 2
an electron-lacuna pair is generated, which triggers an avalanche process of multiplication of the electric charges very quickly (hundreds of ps), which outputs a macroscopic current signal
Data Source
Figure 1~2A
Figure 3~4
Figure 5
AI summary
The invention relates to a system and method for detection, localization and signaling of single photon events and of at least two photons time coincidence events. The system (100) comprises at least one array (M; MM) of pixels (10), each of which comprises a photodetector (12) and a front-end electronics (14), which outputs a digital signal (Sd1,...Sdx). The system (100) further comprises at least one event detection electronics (20) including: a plurality of digital-to-analog transducers (21), one for each pixel (10) of the array (M; MM), configured to convert the digital signal (Sd1,...Sdx) coming from the respective pixel (10) in a corresponding analog signal (Sa1,...Sax), which is quantized in amplitude and duration; an analog adder node (22) configured to sum the analog signals (Sa1,...Sax) coming from the digital-to-analog transducers (21), thereby obtaining a sum analog signal (Sa); and an overall analog-to-digital transducer (24). The overall analog- to-digital transducer (24) comprises at least one first comparator (25) and a second comparator (26), which are operatively connected to the analog adder node (22), wherein the first comparator (25) is configured to compare an output signal (Sout) of the analog adder node (22) with a first threshold (TH1) corresponding to the triggering, within a coincidence time window, of a number of pixels greater than or equal to a first predetermined value, and wherein the second comparator (26) is configured to compare the output signal (Sout) of the analog adder node (22) with a second threshold (TH2) corresponding to the triggering, within a coincidence time window, of a number of pixels greater than or equal to a second predetermined value. The first comparator (25) and the second comparator (26) are configured to output a digital signal (Sd1F,...SdyF) if the output signal (Sout) of the analog adder node exceeds, respectively, the first threshold (TH1) or the second threshold (TH2), thereby allowing event detection, within the time coincidence window, with a number of photons incident on the array (M; MM) greater than or to the first or second value of triggered pixels (10).