A New Class Of Weighting Functions Readily Available With Sampled Data Processors

By using an analog prefilter and a sampled data processor, it is possible to easily implement an entire class of weighting functions. Their main feature is a finite time duration; an additional interesting property is the small number of samples needed to process a pulse. Flat tops witlun better than 1% accuracy can also be achieved. Possible implementations of these filters are discussed with emphasis on causes of inaccuracy. In particular, these filters come out to be time-variant. Synchronization issues are therefore developed and thoroughly discussed. In a mixed analogdigtal implementation, particular regard should be gven to the A/D converter: the requirements on its characteristics are derived. On the contrary, once a pulse is sampled and digitized, the realization of a delay line is straightforward, since it can be obtained with memory elements arranged, e.g., in a shift regrster. The availability of analog to Qgital converters of ever increasing speed and quality makes it also possible to conceive Delay Line shapers obtained with Qgital techniques. In fact, one processor based on switched capacitor filters has been reported, suitable for the LHC experiment at CERN [2]. In this paper, we examine the conditions that the digital filter should fulfill in order to obtain a signal shaping that retains a finite duration of the impulse response once a particular analog prefilter is chosen. The well known Delay Line, Double Delay Line shapers as well as those shapers described in [2] are obtained as particular cases. Some effects due to the non idealities of the filters are also dealt with, together with a discussion of synchronization issues.