The mixed analog/digital shaper of the LHCb preshower

The LHCb preshower signals show so many fluctuations at low energy that a classical shaping is not usable at all. Thanks to the fact that the fraction of the collected energy during a whole LHC beam crossing time is 85%, we studied the special solution we presented at Snowmass 1999 workshop. This solution consists of 2 interleaved fast integrators, one being in integrate mode when the other is digitally reset. Two track-and-hold systems and an analog multiplexer are used to give at the output 85% of the signal plus 15% of the previous one. These 15% are digitally computed from the previous sample, and subtracted. A completely new design of this solution had to be made. This new design is described, including new methods to decrease the supply voltage and the noise, as well as to increase the quality of the reset and the linearity. An output stage, consisting of an AB class push-pull using only NPN transistors is also described. Laboratory and beam test results are given. (5 refs).