Research Of Clock Distribution And Data Transmission In LAWCA Readout Electronics

Cosmic rays are high energy particles from the outer space, consisting of charged particles and a small amount of gamma photons and neutrinos, which are the material we can receive from the outer space. The high-energy cosmic rays carry a large amount of messages about macrocosm, microcosm and space environment, linking the cosmogony, the evolution of stars, the matter distribution in space and many unsolved science mysteries. Cosmic rays can help human to construct the model of the origin of the universe.In order to make great contribution in the process from "100sources era" to "1000sources era" of the very high energy gamma-ray astronomy, physicists in China propose to establish the Large Area Water Cherenkov Array (LAWCA) in Tibet.The front-end digitization architecture is implemented in LAWCA readout electronics. In this architecture, digital signals instead of analog signals are transmitted from the front end via optical fibers, so that the deteriaration of analog signal can be greatly decreased and the system cost can be reduced as well. However, it introduces new challenges. Since digitization is done in the frontend, precise charge and time measurement plays a high requirement on the clock distribution over a large area, accompanied by the increase of data volume. High performane clock distribution and precise phase alignment, as well as high speed data transferring are the challenges for this architecture, which are studied in this dissertation.The research content of this dissertation consists of two parts:clock distribution and data transmission. Regarding the clock distribution, the high precision of time measurement requires high performance clocks distributed to FEE. Besides, clocks must be associated with the global absolute time, and be able to compensate the delay variation caused by ambient temperature fluctuation, etc. As for data transmission, high speed transferring method must be studied. Data transferring, clock distribution, as well as commands transferring is integrated within the same transmission path in this system.The structure of this dissertation is as follows:Chapter1is introduction. It introduces the background, purpose and structure of LAWCA experiment. Then the indicators, technical route and structure of readout electronics are presented. The last part lists the research content of this dissertation. In Chapter2, several clock distribution and data transmission schemes for large-scale physics experiments are described. Through the analysis of the techniques in these experiments, these schemes may provide important references for the clock distribution and data transmission design in the LAWCA experiment.In Chapter3, the requirements of clock distribution and data transmission are analyzed first, which lead to two key techniques used in the electronics:precise synchronous clock distribution for a large area and mixed transmission of data, command and clock. Then we discuss how to implement the two key techniques in detail.In Chapter4, how to design and implement the specific electronics is introduced. First, the overall structure of the clock distribution and data transmission system is described, with the block diagram and work flow as well. Then the main three parts of electronics (clock source module, clock and data transmission module, clock receiving and data sending module of FEE) are described in detail.In Chapter5, we present the performance test results of the electronics system. First, the test methods and testing platform setup are introduced. Then we tested the clock performance, including jitter performance, phase automatic compensation, synchronization of the global time benchmark and stability. At last, the performance of high speed data transmission is tested, consisting of the error test and eye diagram test.In Chapter6, the conclusion and outlook of the future work are introduced.