A Programmable High-Resolution Ultra-Fast Delay Generator

This paper presents a high-resolution, low-dead-time digital delay method in which the performance is independent of the total delay time. We have implemented a low-dead-time (50 ns) and high-resolution (±0.9 ns) delay generator with delay times up to hundreds of milliseconds. We propose high-resolution whole-body positron emission tomograghy (PET) with a 12-module photomultiplier tube-quadrant- sharing (PQS) detector design. This high-resolution delay unit is an important part of the new PET electronics in which a high-yield pileup event recovery (HYPER) method is used. Using the HYPER method, the energy/position signals are generated or digitized upon the arrival of the next event (arriving at a random time after the present event). If the present event is piled up by the next event, the energy/position signals are no longer synchronized with the leading edge of the triggering signal. To detect a coincidence event by using the HYPER method, the original trigger signal must be delayed by a fixed time (1.5 μs for a PET using a bismuth germinate crystal) and a new synchronization process must also be set up between the delayed trigger and the energy/position signals before being passed to the coincidence detection electronics. Each HYPER processor requires 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 in which a delay is needed to synchronize the fast timing trigger to the slower integration or detection address outputs; this low timing jitter delay can also be applied to automatic test equipment and communications.