V812

The CAEN Mod. V812 is a 1-unit wide VME module housing a 16 channel constant fraction discriminator. The module accepts 16 negative inputs and generates precise ECL pulses when the input signals exceeds a given threshold: constant fraction technique allows to precisely determine the timing of the discrimination. The pulse forming stage of the discriminator produces an output pulse whose width is adjustable in a range from 12 ns to 206 ns (typical values) via VME.

Moreover, in order to protect against multiple pulsing, it is possible to program via VME a dead time, from 118 ns to 1625 µs (typical values) , during which the discriminator is inhibited from retriggering. The discriminator thresholds are individually settable via VME in a range from -1 mV to -255 mV (1 mV step) through an 8-bit DAC. Each channel can be turned on or off via VME by using a mask register. A Current Sum output generates a current proportional to the input multiplicity, i. e. to the number of channels over threshold, at a rate of -1.0 mA per hit (-50 mV per hit into a 50 Ω load). The module can operate also with small (below 10 mV) input signals. A MAJORITY output provides a NIM signal if the number of input channels over threshold exceeds the MAJORITY programmed value. Several V812 boards can be connected in a daisy chain via the Current Sum output: in this case, by switching the majority logic to External, it is possible to obtain a Majority signal when the number of active channels in the chained modules exceeds a global Majority level. The logic OR of discriminator outputs is available on a front panel NIM signal.