The performance of the SCT128A ASIC when reading out irradiated and non-irradiated VELO prototype detectors

The measurement of the SCT128A ASIC pulse shape when reading out non-irradiated and irradiated prototype detectors for the LHCb VELO is presented. The detectors studied were non-irradiated and irradiated n-on-n PR01 prototype detectors fabricated by Hamamatsu, and an irradiated p-on-n PR02 prototype detector fabricated by MICRON. The rise and optimal readout times were measured for these detectors, where the rise time is defined as the time for the response to rise from 10% of its maximum value to 90%, and the optimal sampling time is the time at which the response is maximised given the constraints that the underspill and overspill fractions at -25 ns and +25 ns respectively be 30% or less.