Leading-Edge TDC Sampling for Precise PMT Pulse Timing
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Solution Overview
Problem
Current PET imaging systems face challenges in achieving accurate timing resolution due to limitations in the detection of PMT output signals, particularly in determining the transit time across channels, which affects the spatial resolution and time-of-flight calculations.
Innovation Solution
A semiconductor device with a threshold determination unit, comparator circuits, time-to-digital conversion circuits, and an adjustable low-pass filtering unit dynamically determines threshold values and samples the leading edge of PMT signals with high accuracy, enabling precise timestamp determination and energy calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ADC sampling is used to determine PMT signal timing, then the device complexity remains manageable, but the timing resolution and measurement precision are insufficient (cannot achieve 15-25 ps resolution)
Solution Approach 1:
The patent segments the signal processing task by separating the high-precision timing measurement from the full signal acquisition. A dedicated TDC circuit segment handles only the leading edge timing measurement with 15-25 ps resolution, while the ADC handles the rest of the signal at lower precision. This segmentation allows each component to be optimized for its specific function without requiring the entire system to have ultra-high precision capabilities.
Solution Approach 2:
The patent introduces an intermediary mechanism (the TDC circuit with threshold determination unit) that mediates between the PMT signal and the final timing measurement. This intermediary specifically targets the leading edge portion of the signal to extract timing information, allowing the main ADC to operate at lower precision while still achieving overall high timing resolution through the intermediary's specialized function.
2Measurement precision
If the sampling rate is increased to capture more leading edge samples, then the measurement precision improves, but the productivity and processing speed decrease
Solution Approach 1:
The patent extracts only the essential timing information from the signal's leading edge using the TDC circuit, rather than requiring the entire signal to be sampled at ultra-high rates. By taking out just the timing parameter from the leading edge portion, the system achieves high measurement precision without the productivity penalty of uniformly high-rate sampling across the entire signal.
Solution Approach 2:
The patent applies partial action by focusing measurement resources exclusively on the leading edge portion of the signal where timing information resides, rather than applying high-precision sampling across the entire signal duration. This partial focus on the critical region achieves the necessary measurement precision without the excessive processing burden of全面提升 the entire signal processing chain.
3Measurement precision
If discrete elements are used for arrival time determination, then the ease of manufacture is maintained, but the measurement precision is limited and cannot achieve significant accuracy
Solution Approach 1:
The patent merges the threshold determination function with the ADC's comparator circuits, utilizing existing hardware resources to achieve high-precision timing measurement. By merging the TDC's threshold needs with the ADC's inherent comparison capability, the system achieves improved measurement precision without adding completely separate discrete timing elements, thus maintaining ease of manufacture while enhancing performance.
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 approach enhances the timing resolution to 15-25 ps, improving the accuracy of timestamp determination and energy measurement, thereby increasing the spatial resolution and efficiency of PET imaging systems.
Implementation Method 1
an adjustable low-pass filtering unit that filters an output of the PMT
Implementation Method 2
a plurality of comparator circuits that each compare a corresponding threshold value of the plurality of threshold values against a filtered output of the low-pass filtering unit
Implementation Method 3
at least one time-to-digital conversion circuit that is connected to each of the plurality of comparator circuits and that outputs a plurality of time values
Implementation Method 4
PET imaging relies on the conversion of gamma rays into light through fast and bright scintillation crystals
Data Source
AI summary
A method and electronic device for outputting time values and energy of an analog input signal by dynamically determining a plurality of threshold values, comparing, using a plurality of comparator circuits, the plurality of threshold values against the analog input signal, outputting, using at least one time to digital conversion circuit connected to each of the plurality of comparator circuits, a plurality of time values, each time value output when the analog input signal meets or exceeds a threshold value of the threshold values, filtering the analog input signal, performing, using an analog-to-digital conversion circuit, analog-to-digital conversion of the filtered analog input signal to generate a digital signal, and calculating, in response to receiving a trigger signal, an energy of the digital signal.