Compensation for the settling time and slew rate limitations of the CMS-ECAL Floating Point Preamplifier

The Floating Point Preamplifier of the Very Front End Electronics for the CMS Electromagnetic Calorimeter has been investigated on a 5x6 crystal prototype matrix. Discontinuities at the signal peak were observed in the pulse shape reconstruction from the 40MHz sampled and digitized data. The propositions linked to those observations are described, together with a focalized overview of the detector readout chain. A settling time problem is identified and it is shown that a 5ns delay applied to the ADC clock provides a secure solution. Finally, the implementation in the FPPA design of this delay is presented.