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Document type:
Title:
User's Manual (MUT)
Mod. V812 16 Channel Constant Fraction Discriminator
General description
1.
1.1.
Functional description
The CAEN Model V812 is a 16 CHANNEL CONSTANT FRACTION DISCRIMINATOR housed
in a single width VME module. The module accepts 16 negative inputs and produces 16
differential ECL outputs with a fan-out of two on four front panel flat cable connectors (a
functional block diagram is shown in Fig. 1.2). Several version are available, refer to Table 1.1
for details.
Each channel can be turned on or off via VME by using a mask register (Pattern of Inhibit). The
pulse forming stage of the discriminator produces an output pulse whose width is adjustable in
a range from 15 ns to 250 ns via VME. Moreover, in order to protect against multiple pulsing, it
is possible to program via VME a Dead Time during which the discriminator is inhibited from
retriggering. The maximum time walk is ±400 ps (for input signals in the range from -50 mV to -
5 V with 25 ns rise time). The constant fraction is 20%. The constant fraction delay is defined by
a delay line network of 20 ns with 5 taps (see fig. 2.2). The discriminator thresholds are settable
via VME in a range from -1 mV to -255 mV (1 mV step) through an 8-bit DAC.
The module can operate also with small (below 10 mV) input signals, though in this case the
Constant Fraction operation is not performed, i.e. the walk is higher. VETO and TEST inputs
are available on the front panel. The front panel is provided with a Current Sum output that
generates a current proportional to the input multiplicity, i. e. to the number of channels over
threshold, at a rate of
"MAJORITY" output provides a NIM signal if the number of input channels over threshold
exceeds the MAJORITY programmed value. The logic OR of discriminator outputs is available
on a front panel connector. The relevant "OR" LED lights up if at least one of the unmasked
channels is over threshold. The module's operations are completely controlled via software for
each channel through the VME bus. The most important are:
•
setting the discriminator thresholds (8 bit data) from -1 to -255 mV.
•
setting pattern of inhibit; each channel can be turned "ON" or "OFF" by using a mask
register.
•
setting output pulse width
•
setting the Majority threshold value.
•
selection of the Dead Time value.
NPO:
00101/97:V812x.MUTx/04
-1.0 mA per hit (-50 mV per hit into a 50 Ohm load) ±20 %. A
Filename:
V812_REV4.DOC
Revision date:
Revision:
20/04/2009
4
Number of pages:
23
Page:
5
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