A Linear Time-Over-Threshold Digitizing Scheme and Its 64-channel DAQ Prototype Design on FPGA for a Continuous Crystal PET Detector
A Linear Time-Over-Threshold Digitizing Scheme and Its 64-channel DAQ Prototype Design on FPGA for a Continuous Crystal PET Detector
复制标题
用于连续晶体 PET 探测器的线性超阈值时间数字化方案及其 FPGA 上的 64 通道 DAQ 原型设计
DOI：
10.1109/tns.2013.2293758
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发表时间：
2014-02-01
影响因子：
1.8
通讯作者：
Liu Chong
中科院分区：
文献类型：
--
作者：
Wang Yonggang;Cheng Xinyi;Liu Chong
我们提出了一个实用的一般方法，称为线性时间超过阈值（线性TOT）计划，核脉冲幅度数字化，旨在提供一个高集成度的高通道计数探测器系统。该方案中最关键的技术是，对于不同的粒子探测器和不同的脉冲整形，如何产生随时间变化的动态阈值电压，使核脉冲的峰值幅度与TOT时间宽度之间实现线性转换。与常规的脉冲幅度数字化方法相比，线性TOT具有严格的线性度、大的可测信号动态范围和良好的信噪比。利用该方案，我们设计了一个基于现场可编程门阵列（FPGA）的64通道数据采集（DAQ）系统的原型连续晶体POSTRON发射断层扫描探测器。该系统仅由64通道有源RC积分器和电压比较器、共享的动态阈值产生电路和FPGA组成。该系统的物理尺寸非常小，可以连接在PMT的底座上。初步测试结果表明，脉冲幅度与TOT时间宽度的非线性约为0.01%，符合谱测量的能量分辨率可达12.3%，优于采用常规模数转换技术设计的自制数据采集系统的能量分辨率（14.6%）。设计结果表明，线性TOT方案不仅具有高性能，而且集成度高，是核探测中高通道数数字化系统的有效解决方案。
We propose a practical general method, called the linear time-over-threshold (linear TOT) scheme, for nuclear pulse amplitude digitization aiming at providing a high degree of integration for a high-channel count detector system. The most critical technique in the scheme is that for a different particle detector and diverse pulse shaping, how to produce the time-varying dynamic threshold voltage, which enables the linear conversion from the peak amplitude of nuclear pulse to the TOT time width. Compared with the normal time-over-threshold method for pulse height digitizing, the linear TOT has a strict linearity, large measurable signal dynamic range, and good signal-to-noise ratio. Using the scheme, we design a prototype of a field-programmable gate-array (FPGA)-based 64-channel data-acquisition (DAQ) system for a continuous crystal poistron emission tomography detector. The system only consists of 64-channel active RC integrators and voltage comparators, a shared dynamic threshold generating circuit, and an FPGA. The physical size of the system is so small that it could be attached on the base of the PMT. The preliminary test results show that the nonlinearity between pulse amplitude and TOT time width is about 0.01%, and the prototype could achieve an energy resolution of 12.3% by coincident spectrum measurement, which is better than the result (14.6%) obtained using our previous homemade DAQ system designed with a normal analog-to-digital converter technique. The design proves that the linear TOT scheme is an effective solution for a high-channel count digitizing system in nuclear detection, not only for its high performance, but also for a high degree of integration.