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The Research on the Timing Synchronization Technology with High Precision for Large Scale Physics Experiments

Author: LiCheng
Tutor: AnZuo; LiuShuBin
School: University of Science and Technology of China
Course: Physical Electronics
Keywords: clock system timing system clock jitter clock skew White Rabbitprotocol PTP DDMTD
CLC: TN79
Type: PhD thesis
Year: 2012
Downloads: 254
Quote: 1
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Abstract

In the large physics experiment device, the importance of the clock and timing system for the entire experimental system is same as the blood circulation system for the human body. Therefore, the clock and timing system is the basic requirement for physics experiments.The difficulty of designing the clock and timing system is to ensure the both long-term and short-term stability and accuracy of the clock, to reduce and control the clock skew between channels, to automtically compensate the delay variation of clock which is caused by environmental and other uncontrollable factors. The stability and accuracy of the clock can be remained by use of the domesticated atomic clock and the PLL circiut. In order to compensate for the transmission delay drift of the clock or timing signal, it is necessary to build the round trip of the clock.Through the precision time synchronization protocol (PTP) and the digital Dual Mixer Time Difference (DDMTD), White Rabbit protocol can measure the propagation delay of the round trip of the clock in a high accurate and continuous way. Then the result of the delay measurement can be used to compensate the transmission delay drift of the clock or timing signal. However, the metastable problem is inherent in DDMTD, which will increase the uncertainty of the delay measurement. The application of Time to Digital converter (TDC) based on FPGA, the averaging method and other methods effectively reducs the uncertainty. The improvement of DDMTD is achieved. In addition, the complex network structure of synchronous Ethernet in White Rabbit protocol can be trimmed, and the simple star structure of the clock system can meet the needs of many physics experiments.The specification of the clock system for water Cherenkov detection array (WCDA) at the large high-altitude air shower cosmic ray Observatory is that the clock jitter should be less than100picoseconds, and the clock skew between FEE channels should be less than100picoseconds. Moreover, considering on the range of WCDA, the number of clock channels and the harsh environment, it is a severe verification for the simplied and improved version of the White Rabbit protocol.In this thesis, the first chapter introduces the indicators to measure the clock system, followed by listing the requrements of clock and timing system for the physics experiments. The second chapter investigates the clock system for physics experiments. The advantages and disadvantages of these clocks and timing systems are analyzed.In chapter three, universal methods and protocols of time synchronization is introdued. And the advantages and disadvantages of these methods and protocols are compared.In chapter four, the principles of White Rabbit protocol is analyzed in detail. Then the principle of simplied and improved version of White Rabbit protocol is proposed.In chapter five, the prototype clock system is designed first. Then the prototype clock system is tested.The results are listed as follow:the jitter of distrubited clock is less than40picoseconds; the clock skew between the two channels is still less than70ps when the temperature and length fiber changes.In chapter six, the summary and the outlook of this thesis are introduced.

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