Institut de recherche sur les lois fondamentales de l'Univers

Abstract:
=========
A front-end BiCMOS ASIC was specially developed for the Micromegas detectors to
be used in the Small Angle Tracker of the COMPASS experiment at CERN.  Each of
the 16 channels of this integrated circuit contains a low noise preamplifier
with a 100  ns peaking time filter and a discriminator driving a low-level
differential digital buffer.  The design of the preamplifier and the choice of
the shaping have been tuned to the detector signal shape in order to allow the
operation of Micromegas even for very low multiplication gain values.  Noise
measurements show an equivalent noise charge of less than 1500  e- rms for a
detector capacitance of 40pF.  The measured performances of this ASIC
associated or not with the detector are fully described in this paper.