Digital Delay
A traditional analog or digital delay device with a longer total delay time requires a larger input pulse width, a slower input pulse rate and generates a slower rise-time output. Our high-resolution small dead-time digital delay method is fully independent of the total delay time.
We have implemented a small dead-time (50 ns) and high-resolution (<0.9 ns) delay generator with the total delay time up to hundreds 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 using a pileup prevention method (HYPER).
HYPER uses a dynamic integrating method, which means the measured energy and position signals are no longer synchronized with the leading edge of the present triggering signal because the energy and position signals are generated or digitized at the arrival of the next event (arriving at a random time from present event). To detect a coincidence event by using the HYPER method, the original trigger signal has to be delayed by a fixed time (1.5 µs) and a new synchronization process has to be set up between the delayed trigger and the energy/position signals before they can go to a coincidence procedure. Each Anger HYPER camera needs one delay generator, and there are 48 delay units inside the whole camera. This delay generator also can be used in other applications such as automatic test equipment and communications.
Delay Unit's Role in the HYPER Circuit
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