THE OPAL SILICON-TUNGSTEN CALORIMETER FRONT-END ELECTRONICS

A pair of small angle silicon-tungsten (Si-W) calorimeters has been bu ilt to measure the luminosity to a precision better than 0.1% in the O PAL experiment at the Large Electron Positron (LEP) collider at CERN n ear Geneva. Each calorimeter contains 19 layers of tungsten (W) plates and silicon (Si) detectors, corresponding to a total of 22 radiation lengths, sampled by about 1 m2 of detectors divided into 304 x 64 inde pendently read out channels. A complete electronics system has been de veloped, from the preamplifier up to the VME read out and control inte rface. It includes a fast trigger based on analogue sums. This paper d escribes how a large number of channels have been implemented in a den se environment, thanks to the use of ASIC's directly bonded on the det ector.