Re: Discriminators

[Richard Jones <richard.t.jones@uconn.edu>]

Colleagues,

Another thing we should review during tomorrow's meeting is our 
specification of CFD's to read out the tagging counters.  Originally I 
had requested CFD's for both the microscope and the fixed array (and the 
PS counters as well) but then I think that Franz might have changed his 
mind and requested LE discriminators instead, to increase the efficiency 
at high rates.  I started thinking about this as well, and asked 
Fernando what the specs are for the pulse shape requirements for the two 
types of discriminators.  Let's talk about the pros and cons of each at 
tomorrow's meeting.  The pulses that come from the SiPM preamplifiers 
that we are currently designing are too fast to meet the specs for the 
CFD's.  Do we want to slow down the preamps, or switch to LE discs?  I 
would guess that the LE's are quite a bit cheaper, which means it is 
hard to go back once the switch to LE's has been made.

-Richard Jones


Fernando J. Barbosa wrote:
> Hi Richard,
>
> I have attached two files (user manuals) for CFD and LE discriminators 
> from CAEN.
>
> For the CFD, the minimum output pulse width is about 15 ns, 
> corresponding to a 66 MHz rate capability. There is a programmable 
> deadtime, if needed, for a minimum of 150 ns but I don't think we 
> would be interested in that. The delay for the CFD is internally 
> settable from 4 ns to 20 ns (4 ns steps) and this implies that the 
> fastest rise time for input pulses is about 5 ns ( 5 ns x 0.8 = 4 ns 
> delay) with a fraction of 20%. This is OK for fast PMTs with long cables.
>
> The LE has a minimum output pulse width of 5 ns with a douple pulse 
> resolution of 7 ns. So, this is good for about 140 MHz.
>
> Let me know if you need additional information.
>
> Regards,
> Fernando