7.2.2 ZERO SUPPRESSION
The implementation of a Zero Suppression (ZS) mechanism is necessary as soon as
a high number of pulses are sampled simultaneously by DSCs. In case of the 240
CsI crystals of the calorimeter, a 70 MeV photon or positron is contained
in a cluster of about 7 crystals. A pion beta event consists thus of about 14
signals, the rest of the signals do not carry any information.
Figure
7.3:
The Zero Suppression part of the DSC V4. Depending on the status of the
flip-flop FF ZS, the RBI ZS is transmitted to the RBI S or the RBO ZS. In
order to implement the ZS mechanism, the pad RBI S is connected to the RBI pad
(Fig. 7.1) and the RBO pad (Fig. 7.1) is connected to the RBO S pad.
On each DSC a ZS circuit is implemented. The principle of the ZS mechanism is
to read out only those DSC channels which carry significant pulse information:
The input pulse must be above a user-defined threshold and within a
user-defined time gate (see Fig. 7.3). If both of these requirements are
fulfilled, the flip-flop FF ZS is set and the RBI ZS pulse is
transmitted to the RBI-pad of the sampling part of the DSC. If one or both of
the requirements are not fulfilled, the RBI ZS is transmitted directly to
the output of the ZS (RBO ZS), which is connected to the RBI ZS of the next DSC
in the chain. Whenever the read-out phase is started, the "route" of the RBI
pulse is fixed, i.e. it is defined which of the DSCs are to be read out and
which are not.