Dual-TDC Timing Circuit for Silicon Photomultiplier Time Resolution
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Solution Overview
Problem
Meta-stability in timing circuits of radiation detectors for PET systems leads to inaccurate timestamp measurements, reducing the precision of coincidence detection and introducing noise into images due to the susceptibility of flip-flops to meta-stable states during setup or hold times.
Innovation Solution
A timing circuit with two non-synchronous time-to-digital converters (TDCs) is used, each synchronized to a unique reference clock, providing independent timestamps to correct for meta-stability issues and improve time resolution, with a comparator to detect differences and initiate synchronization or reset as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single TDC synchronized to one reference clock is used, then the device complexity is low, but the time resolution and measurement precision are reduced due to meta-stability
Solution Approach 1:
The patent divides the timing measurement function into two separate TDCs, each synchronized to a different reference clock signal. This segmentation allows independent timestamp generation that avoids the meta-stability problem affecting single-TDC systems, thereby improving time resolution while managing complexity through functional division.
Solution Approach 2:
The patent changes the synchronization parameter by using two different reference clock signals instead of a single shared clock. This parameter change enables each TDC to operate independently without meta-stability interference, improving measurement precision while the complexity increase is offset by the elimination of meta-stability correction requirements.
2Reliability
If flip-flops are used in synchronous circuits for event detection, then the ease of operation is improved, but the reliability deteriorates due to meta-stability during setup or hold times
Solution Approach 1:
The patent introduces a comparator as an intermediary device that processes the output signals from both TDCs. This comparator mediates the timestamp data, identifying valid timestamps and correcting for any meta-stability-related errors, thereby improving reliability while maintaining ease of operation through automated correction.
Solution Approach 2:
The system implements feedback through the comparator that monitors timestamps from both TDCs and identifies valid measurements. This feedback mechanism automatically corrects for meta-stability issues by selecting reliable timestamps, improving system reliability while requiring minimal operator intervention.
Data Source
AI summary
A radiation detector module (10) for use in a time-of-flight positron emission tomography (TOF-PET) scanner (8) generates a trigger signal indicative of a detected radiation event. A timing circuit (22) including a first time-to-digital converter (TDC) (30) and a second TDC (31) is configured to output a corrected timestamp for the detected radiation event based on a first timestamp determined by the first TDC (30) and a second timestamp determined by the second TDC (31). The first TDC is synchronized to a first reference clock signal (40, 53) and the second TDC is synchronized to a second reference clock signal (42, 54), the first and second reference clock signals being asynchronous.