A White Rabbit-Synchronized Accurate Time-Stamping Solution for the Small-Sized Cameras of the Cherenkov Telescope Array

• Published in: IEEE transactions on instrumentation and measurement 2021, Vol.70, p.1-14
• Main Authors: Sanchez-Garrido, Jorge, Jurado, Antonio, Jimenez-Lopez, Miguel, Balzer, Arnim, Prokoph, Heike, Stephan, Maurice, Berge, David, Rodriguez-Alvarez, Manuel, Diaz, Javier
• Format: Article
• Language: English
• Subjects: Arrays; Camera; Cameras; Cherenkov; Cherenkov telescope array (CTA); Converters; direct memory access (DMA); Ethernet; field-programmable gate array (FPGA); Gamma rays; Hardware description languages; High speed; IEEE 1588; Modules; Nodes; Rabbits; Stamping; Synchronism; Synchronization; System on chip; Telescopes; Time synchronization; time-to-digital converter (TDC); timing; White Rabbit (WR)
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2020.3013343

This article presents the Zynq-embedded node for the Cherenkov telescope array (ZEN-CTA) node, a programmable system-on-chip (SoC) with White Rabbit (WR)-synchronization capability. It targets a solution for the uniform clock and trigger time-stamping module of the small-sized telescopes in the CTA. This module is tasked as a distributed acquisition device with a focus on obtaining time stamps for candidate Cherenkov events, which could be generated at potentially high rates from very-high-energy gamma rays and their subsequent distribution over Ethernet. In this context, the customized design of the ZEN-CTA node is examined thoroughly, including its generic implementation aspects and its main functional blocks. The design of the WR-assisted time-to-digital converters (TDCs) for time-stamping analog triggers is presented in detail alongside the implementation of an upgraded high-speed data path (1 Gb/s) for the WR-compatible Ethernet interfaces of the node. The new data path will feature a direct memory access engine for direct software transmissions and a hardware description language (HDL) coprocessor for high-speed forwarding. Next, the time-stamping accuracy of the WR-enhanced TDCs will be characterized alongside the forwarding efficiency of the new data path. Finally, conclusions are drawn, and the main contributions of this research are enumerated, a potential deployment within the CTA infrastructure to support the acquisition of Cherenkov light is considered, and additional use cases are mentioned.