SCOTT: A time and amplitude digitizer ASIC for PMT signal processing

SCOTT is an ASIC designed for the readout electronics of photomultiplier tubes developed for KM3NeT, the cubic-kilometer scale neutrino telescope in Mediterranean Sea. To digitize the PMT signals, the multi-time-over-threshold technique is used with up to 16 adjustable thresholds. Digital outputs of discriminators feed a circular sampling memory and a “first in first out” digital memory. A specific study has shown that five specifically chosen thresholds are suited to reach the required timing accuracy. A dedicated method based on the duration of the signal over a given threshold allows an equivalent timing precision at any charge. To verify that the KM3NeT requirements are fulfilled, this method is applied on PMT signals digitized by SCOTT.