Gérard Bohner, Remy Cornat, Alain Falvard, Evgueni Gushin*, Jacques Lecoq, Jena-Yves Maulat, Pascal Perret, Cyrille Trouilleau.  Laboratoire de Physique Corpusculaire, Université Blaise Pascal & *Institute for Nuclear Research (INR), Moscow, Russia.
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Signals provided by preshower cells and read by photomultipliers have been simulated by Monte-Carlo method and directly measured. This measure uses a cosmic ray set up and takes fully simulated LHCb events into account. This allowed us to define the shape and the dynamic of signals. The 64 channels of the photomultipliers have various gains according to output. This leads to localize analog signal processing units very close to the photomultipliers in order to easily tune-up the gains. Close to PMs, the 64 electronics channels process analog signals, which are sent in differential mode to the crate where they are digitized, processed and stored.

The analog signal processing units are designed with some dedicated full-custom electronic circuits. In order to have a sufficient accuracy in spite of a large signal shape disparity at low energies, the signal is integrated and then cleared. Due to the pile-up probability, the integration time is limited to 25ns corresponding to the beam crossing period in LHC. To improve the resolution, this maximum integration time is choosed. This requires to use two interlaced switched integrators per channel. Some track-and-hold units sustain the integration final value. Then, by using a time multiplexing method, integrated signal values are sent at 40 MHz rate to 64 channels cards.

In the crate, signals are digitized with commercial ADCs. To avoid pile-up problems, we substract a fixed proportion of the last value from the current value. This process and the calibration task are done with two look-up tables which provide energy values used by the trigger system and by the memories for the DAQ

Physical data, electronic architecture, simulations results and measurements on the first prototype of the design will be presented.

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Due to the fluctuating signal shape and the 40 MHz beam crossing frequency, the LHCb calorimeter preshower cell read out requires a specific microelectronic design including two interlaced switched 20MHz integrators.  Thsi paper describes the present status of the design.
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