A Scalable Synchronized Timing System for Digital PET

It is important to synchronize the data acquisition when digitizing PET event pulses with multiple detectors. In this paper, we design and implement a basic clock distribution module, the module can provide 12 synchronized reset and clock outputs. By connecting several modules, it is practical to build a larger clock distribution system in a tree structure. The tree structure is applicable to the digital PET system of different scale, when the height of the tree is 3, the system can drive 1728 detectors. We built a simplified three-level clock distribution system, the clock period standard deviations were measured to be below 20 ps, the clock skews between two lock distribution modules were below 50 ps, and the reset skews were below 100 ps. To prove that the tree structure does not lead to significant loss on the timing performance, we set up a PET detector ring consisting of 6 detectors, the detectors were driven by twolevel clock distribution system. The energy resolution obtained was 18.1% and the coincidence resolving time was 535 ps. As a comparison, when using a single clock distribution module, the energy resolution and the coincidence resolving time obtained were 17.9% and 538 ps respectively.