Synchronization Algorithm in Time-to-Digital Converters Networks
Synchronization Algorithm in Time-to-Digital Converters Networks
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DOI：
10.1109/nss/mic42677.2020.9507892
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
F. Garzetti;N. Lusardi;N. Corna;S. Salgaro;G. Meanti;Angelo Geraci
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文献类型：
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作者：
F. Garzetti;N. Lusardi;N. Corna;S. Salgaro;G. Meanti;Angelo Geraci
核物理实验和医学成像技术，如正电子发射断层扫描（PET）正在通过时间分辨实验。此外，所观察到的现象越来越复杂，必须通过仪器集群的互连来建立一个装置。从这个意义上说，经典的时间-数字转换器（TDC）结构并不令人满意，因为一个测量单元的通道数量并不足够。在这方面的贡献，实现了基于现场可编程门阵列（FPGA）的TDC的网络。这一贡献的目的是提供达到大量通道的可能性，只需连接托管在不同设备中的TDC，而不会损失精度和分辨率。此外，为了保证快速原型和灵活性，所有的同步算法和TDC的可编程逻辑实现。这种实现背后的想法是一种分布式架构，由多个高分辨率TDC（皮秒单位）组成，并获得时间戳，就像它们来自单个设备一样。挑战主要由组成网络的设备的时钟频率差异决定，并且可以涉及两个问题：偏移导致不同设备上的时间戳的不同值，以及增益误差，其确定用于测量的不同最低有效位（LSB）。最相关的问题，第二个问题，它是通过在每个TDC中添加一个额外的通道来解决的，称为同步，它负责组成网络的所有设备之间的同步。以这种方式，同步负责测量TDC之间相对于公共信号的时钟偏差，并因此归一化所有时间戳。
Nuclear physics experiments and medical imaging techniques like Positron Emission Tomography (PET) are moving through time- resolved experiments. Furthermore, the increasing complexity of the phenomena under observation makes mandatory to build a set-up by means of the interconnection of an instrumentation cluster. In this sense, classical Time-to-Digital-Converter (TDC) structure is no more satisfactory, since the number of channels of one measuring unit is no more sufficient. In this contribution, the implementation of a network of TDCs based on Field Programmable-Gate Arrays (FPGAs) is presented. Aim of this contribution is to give the possibility to reach a huge amount of channels, simply by connecting TDCs hosted in different devices without loss in term of precision and resolution. Furthermore, to guarantee fast prototyping and flexibility, all the synchronization algorithm and the TDC are implemented in programmable logic. The idea behind this implementation is a distributed architecture composed of multiple high-resolution TDCs (units of picoseconds) and obtain the timestamps as if they were coming from a single device. The challenge is mainly dictated by the differences in clock frequencies of the devices that compose the network, and can be referred to two problems: the offset leading to different values for the timestamps on different devices, and the gain error, which determines different Least Significant Bits (LSBs) for the measurements. The most relevant problem, the second one, it is addressed by adding an extra channel in each TDC, called sync, which takes care of the synchronization between all the devices which compose the network. In this way, the sync is in charge to measure the clock skew between the TDCs respect to a common signal and consequently normalize all the timestamps.