Re: Discriminators

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hi Richard,

What time is tomorrow's meeting? 9:30?

Thanks,
Fernando

Richard Jones wrote:
> 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
>
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