  The GRIT (Granularity, Resolution, Identification, Transparency) Silicon
array is intended to measure direct reactions. Its design is based on several
layers (three layers in the forward direction, two backward) of custom-made
trapezoidal and square detectors. The first stage is 500 {\mu}m thick and
features 128x128 orthogonal strips. Pulse shape analysis for particle
identification is implemented for this first layer. Given the compacity of this
array and the large number of channels involved (>7,500), an integrated
preamplifier, iPACI, that gives charge and current information has been
developed in the AMS 0.35 {\mu}m BiCMOS technology. The design specifications
and results of the test bench are presented. Considering an energy range of 50
MeV and an energy resolution (FWHM) of 12 keV (FWHM) for the preamplifier, the
energy resolution for one strip obtained from alpha source measurement in real
conditions is 35 keV. The current output bandwidth is measured at 130 MHz for
small signals and the power consumption reaches 40 mW per detector channel. A
first beam test was performed coupling a nTD trapezoidal double-sided stripped
Silicon detector of GRIT with the iPACI preamplifier and a 64-channel
digitizer. Z=1 particles are discriminated with pulse shape analysis technique
down to 2 MeV for protons, 2.5 MeV for deuterons and 3 MeV for tritons. The
effect of the strip length due to the trapezoidal shape of the detector is
investigated on both the N- and the P-side, showing no significant impact.
