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Re: Flash ADC Timing
Hi All,
some time ago Elliot sent around a mail asking what is needed in terms
of electronics on DAQ
at the Universities. I answered to that question that here at IU we have
no VME based equipment
at all. In particular this means NO crate, NO front end cpu (ROC), NO
other VME based modules.
This means we need a Crate, a ROC and maybe another module I do not know
we need to get
CODA running in addition to the fADC. We have computers that can be used
as back ends
to install CODA on and if the communication is done via ethernet then
all we need on top of that is
a hub and some cables that we have here at IU.
cheers,
Beni
Fernando J. Barbosa wrote:
> Hi Elke,
>
> That's a good idea to start thinking about requests for any sort
> of electronics people will need over the next few months, especially
> in light of CD-3.
>
> We currently have 4 10-bit fADC-250 under tests/debugging and I
> don't expect these will be released until early 2008. We have been
> discussing the possibility of an engineering run, 5-10 boards, in the
> fADC group for use by users and for testing the trigger system. Please
> be aware that it make take up to 8 weeks before we get any new boards
> (ordering components, PCB fabrication, assembly, test).
>
> I will be away on Wednesday, 11/21/07 for the Thanksgiving holiday.
>
> Best regards,
> Fernando
>
>
>
> Elke-Caroline Aschenauer wrote:
>> On Fri, 16 Nov 2007, Matthew Shepherd wrote:
>>
>> Fernando and Matt,
>>
>> i think we all agree test are needed we can do what was suggested in the
>> report. Currently we have 5 250MHz FADCs. I suggest that on Wednesday in
>> the weekly Hall D meeting we find out how many FADCs pleople might need
>> for test stands and than see we have to produce more.
>>
>> bye elke
>>
>>
>>
>>
>>> Date: Fri, 16 Nov 2007 16:46:11 -0500
>>> From: Matthew Shepherd <mashephe@indiana.edu>
>>> To: Fernando J. Barbosa <barbosa@jlab.org>
>>> Cc: halld-cal@jlab.org
>>> Subject: Re: Flash ADC Timing
>>>
>>>
>>> Hi Fernando,
>>>
>>> I understand the claims in the document are rather optimistic;
>>> however, the fact of the matter is that we probably just need timing
>>> resolution roughly on the scale of sampling rate to suppress beam-
>>> related out of time noise.
>>>
>>> If you have a real fADC that is ready for use we're happy to take it
>>> and get it setup and running here. This would serve many purposes --
>>> probably most important at this point is that we could use the real
>>> PMT, light guide, base, and fADC that we plan for the actual
>>> experiment to readout just one bar and probe the low energy threshold
>>> of the calorimeter using cosmic rays (and guidance from simulation).
>>>
>>> -Matt
>>>
>>>
>>> On Nov 16, 2007, at 3:01 PM, Fernando J. Barbosa wrote:
>>>
>>>
>>>> Hi Matt,
>>>>
>>>> I am familiar with those documents and I recall that at the time
>>>> we started developing the fADC (~2 years?), I suggested that
>>>> someone needed to take some real data with Paul's single-channel
>>>> prototype and try doing the prescribed fittings, etc. To the best
>>>> of my knowledge, no one in the collaboration has done that.
>>>>
>>>> Referring to the document, the algorithm relies on finding the
>>>> exact pulse peak and getting the two preceding samples to determine
>>>> the 50% time, for instance. The exact peak was determined from
>>>> sampling at 2.5 GHz (400 ps intervals) and fitting the data with a
>>>> 9th degree polynomial. The data was then "degraded" to provide the
>>>> equivalent of 8 or 10-bit, 250 MHz (4 ns intervals) sampling. Note
>>>> that the exact peak is critical for the algorithm to provide the
>>>> quoted resolution, although these details are missing from the
>>>> document.
>>>>
>>>> The real fADC, and sampling at 250 MHz, will not provide a
>>>> sample of the true pulse peak. I believe that such "fluctuation"
>>>> will degrade the effective resolution considerably. So, I suggest
>>>> that this needs to be checked with a real fADC, perform the
>>>> algorithm on real raw fADC data (offline) and determined the
>>>> effective resolution that can be achieved by this method. Obtaining
>>>> 400 ps resolution from 4 ns data points and from 10 ns pulse rise
>>>> times seems difficult to me. We actually may have to shape (i.e.
>>>> slow) the pulse to get more samples on the leading edge of the
>>>> pulse. Once the algorithm is well understood, it will need to be
>>>> implemented in a relatively simple/compact manner to fit within the
>>>> resources of the FPGAs or board memory. Eventually, any data that
>>>> is passed up the chain must be balanced with the backplane bandwidth.
>>>>
>>>> Let me suggest you set up a test with the real PMTs/bases/
>>>> scintillator/fiber/laser and get data with a real fADC, a TDC and
>>>> CFD. We could lend you one fADC-250 to get the raw data. Let me
>>>> know what you decide and how I can help.
>>>>
>>>> Best regards,
>>>> Fernando
>>>>
>>>>
>>>>
>>>>
>>>> Matthew Shepherd wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> The study I was referring to has been linked to the FCAL page here:
>>>>>
>>>>> http://www.jlab.org/Hall-D/software/wiki/index.php/FCAL
>>>>>
>>>>> This work was done about 3 years ago and claims a resolution of
>>>>> about ~160 ps can be achieved. This is far better than is
>>>>> actually needed to push down backgrounds. I think Scott had in
>>>>> mind another application: using the FCAL to determine the event
>>>>> start time. The algorithm does a transformation of the leading
>>>>> edge of the pulse to determine the start time and depends on
>>>>> having the two samples before the peak on the leading edge.
>>>>>
>>>>> I believe Paul had planned to implement this in a simple lookup
>>>>> table which would require about 65K of memory on the chip.
>>>>> Perhaps that could be optimized even more. It was never
>>>>> investigated in detail mainly because it seemed like something
>>>>> relatively easy to implement. All of these buffers will need some
>>>>> processing -- the drift chambers will also depend on the timing
>>>>> algorithms that are built into the flash ADCs.
>>>>>
>>>>> -Matt
>>>>>
>>>>>
>>>>> <barbosa.vcf>
>>>>>
>>>
>>
>> ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
>> ) `\ -
>> / '. | +
>> | `, Elke-Caroline Aschenauer =
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>>
--
B. Zihlmann
Indiana University
Physics Department
727 E. Third Street
Bloomington, IN 47405
phone: (812) 855 6973
Fax: (812) 855-5533