A Programmable High-resolution Ultra Fast Delay Generator

This paper presents a high-resolution, small dead-time digital delay method where the performance is independent of the total delay time. We have implemented a small dead-time (50ns) and high-resolution (±0.9ns) delay generator with delay time up to hundreds of milliseconds. We have proposed a high-resolution whole-body PET with 12 module PMT-quadrant-sharing (PQS) detector design. This high-resolution delay unit is an important part in the new PET electronics where a high-yield-pileup-event-recovery (HYPER) method is used. Using HYPER method, the energy/position signals are generated or digitized at the arrival of the next event(arriving at a random time from present event) if the the present event was piled-up by the next event, so the energy/position signals are no longer synchronized with the leading edge of the trigggering signal. To detect a coincidence event by using the HYPER method, the original trigger signal has to be delayed by a fixed time (1.5μs for BGO) and a new synchronization process has to be setup between the delayed trigger and the energy/position signals before they can go to the coincidence detection electronics. Each HYPER processor needs one delay generator; there are 48 delay units inside the whole PET system. This high resolution delay generator also can be used in other PET systems where a delay is needed to synchronize the fast timing trigger to the slower integration or detector address outputs; this low timing-jitter delay can also be applied to automatic test equipment and communications.