General-Purpose Data Streaming FPGA TDC Synchronized by SerDes-Based Clock Synchronization Technique

This study proposes a clock synchronization protocol using the functionalities of IDELAYE2 and IOSERDESE2 primitives of an AMD Xilinx field-programmable gate array (FPGA) to serve as a general-purpose data-streaming type time-to-digital converter (TDC) for particle and nuclear physics experiments. A clock synchronization protocol called local area common clock protocol (LACCP) was developed as the upper layer protocol of a proprietary link (MIKUMARI), which was defined prior to this work by a community of users from the experimental physics field in Japan. Clock synchronization is realized using a round-trip time measurement with the system clock period and a fine offset time estimation, which corresponds to the clock signal phase difference between the primary and secondary FPGAs. The fine offset measurement is based on information from the IDELAYE2 and ISERDESE2 primitives utilized as the physical layer of the MIKUMARI link. No extra component is used. The LACCP can be implemented in an FPGA using general IO pin pairs for serial transmission and reception. A streaming high-resolution TDC (Str-HRTDC) was developed based on a tapped-delay-line (TDL) built from CARRY4 primitives in the AMD Xilinx Kintex-7 FPGA. It continuously measures the timing with 19.5-ps intrinsic resolution in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula> and provides unique timestamp information over 2.4 h by introducing the time frame structure defined and synchronized by LACCP. The clock synchronization accuracy and the timing resolution were evaluated by connecting four modules with optical fibers up to 100 m in length. No cable length dependence was confirmed. The obtained synchronization accuracy was approximately 300 ps. The timing resolution between two synchronized modules was 23.1 ps in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma $ </tex-math></inline-formula>.