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Re: Combined tracking meeting
Hi Mitch,
Yes, I agree. We really need to do additional studies/tests with the CDC
and FDC and these may well be performed with the upcoming GAS-2.
By the way, I have not forgotten that I owe you some scope pictures. I
should have them for you soon.
Regards,
Fernando
Mitch Newcomer wrote:
> Hi Fernando, the only think I can see in favor of a 14bit readout is
> that it allows a wide dynamic operational range so that systems with
> widely varying offsets
> and gains could potentially be used with the same ADC without
> requirning modification. The resolution I remember for wire chamber
> measurements
> is something like FWHM = 50% of the measured value. Probably this is
> gas dependent so a high Z gas like Xenon would give higher resolution
> The only place I might imagine using even 10 bit resolution is in
> position extrapolation between pads. - Mitch
>
> Fernando J. Barbosa wrote:
>> Hi Gerard and Mitch,
>>
>> I think it would definitely be helpful to have some Garfield studies
>> performed on the CDC for the various operating conditions. I am also
>> of the opinion that we should definitely plan for some beam studies
>> with the GAS-2. I know it takes resources but there is a lot involved
>> here. As you know, there is a test beam at BNL that we can plan for -
>> I have used it while at BNL a number of years ago while developing
>> the "predecessor" to the CDC and it provided invaluable data. The
>> next small CDC prototype could be slated for this tests.
>>
>> I think it is also a good suggestion to ask Mitch about his
>> experience with various developments and if a 14-bit ADC is
>> reasonable or overkill. Mitch could you comment on this?
>>
>> Certainly the 14-bit option is better than any additional circuitry
>> for a non-linear transfer function. The total cost increase would be
>> about $50k! That's a lot of money, for sure, and this points to the
>> fact that we really need additional studies, as I suggest in the
>> first paragraph. I think you also share that sentiment.
>>
>> Regards,
>> Fernando
>>
>>
>>
>>
>> Gerard Visser wrote:
>>> Hi Elke,
>>> From the quote which I obtained last year, it is about $15 more
>>> per channel to have 14-bit ADC's on the board. There is (according
>>> to spec documents) no change to the power dissipation. [It is
>>> apparently the same chips, just tested to different level of
>>> performance that you buy.] It is probable the price will go down,
>>> probably not by quite that much though.
>>> Nonlinear response will cost much less than $15 per channel, as
>>> long as it fits on the same basic board architecture (which depends
>>> on the details of what we would want to do, of course).
>>> I agree also, the ASIC does some nonlinear transformation, but
>>> on the other hand _that_ may not be very precisely controlled (for
>>> temperature, matching, whatever...). Also, ideally the nonlinearity
>>> would be introduced after all shaping filters so that it can be
>>> precisely and easily un-done by a lookup table in the FPGA, to allow
>>> for integrating the pulse. If the nonlinearity is introduced
>>> earlier, then un-doing it requires some sort of nonlinear digital
>>> filter not just a lookup table.
>>> One final comment, probably it would raise eyebrows to say that
>>> we really need 14-bit resolution from a drift chamber ADC...? We
>>> should for instance get some opinions from Mitch on that. Of course
>>> I will be happy if we do use 14-bits.
>>>
>>> - Gerard
>>>
>>> Elke-Caroline Aschenauer wrote:
>>>> On Wed, 23 Jul 2008, Curtis A. Meyer wrote:
>>>>
>>>> Dear Gerard,
>>>>
>>>> how much more money are we talking for 14bit vs 12bit. Also keep in
>>>> mind
>>>> we will not buy the boards before FY11, so mybe the prise than for
>>>> 14bit
>>>> will be the same as now 12bit, but that is speculation on my side.
>>>> I also prefer even if there is a bit of more money involved to do
>>>> the easy
>>>> straight forward solution instead of a more complicated one. Curtis
>>>> don't
>>>> you want for dE/dx all the signal very well measured.
>>>>
>>>> cheers elke
>>>>
>>>>
>>>>> Date: Wed, 23 Jul 2008 16:49:09 -0400
>>>>> From: Curtis A. Meyer <cmeyer@ernest.phys.cmu.edu>
>>>>> To: Gerard Visser <gvisser@indiana.edu>
>>>>> Cc: GlueX Tracking <tracking@gluex.org>
>>>>> Subject: Re: Combined tracking meeting
>>>>>
>>>>> Hi Gerard -
>>>>>
>>>>> thanks for your comments. Actually, the factor is 60, but if we are
>>>>> willing to compromise on the slow, forward going protons, we could
>>>>> squeeze it.
>>>>>
>>>>> I also talked to Fernando about the non-linear aspect, and he also
>>>>> mentioned that the ASIC will do that for us at some level. It would
>>>>> be good to understand all of the effects involved. Given the
>>>>> option of
>>>>> stuffing the ~45 CDC modules with 14-bit chips might be a good
>>>>> option to consider.
>>>>>
>>>>> Cheers - Curtis
>>>>> On Wed July 23 2008, Gerard Visser wrote:
>>>>>> Hi Curtis,
>>>>>> I read your doc, just wanted to mention that as far as the
>>>>>> ADC125 is
>>>>>> concerned there would certainly be an option either to have it be 14
>>>>>> bits or to apply some nonlinear stage in the analog input signal
>>>>>> conditioning. Actually 14 bits has for a long time been planned
>>>>>> as the
>>>>>> baseline pcb design so it can be stuffed either for 12 or 14 bits
>>>>>> operation, so that all is trivial (except for the higher price of
>>>>>> the 14
>>>>>> bit chips). Nonlinear signal processing needs a lot of detailed
>>>>>> discussion, it is not going to get into this summer's pcb layout,
>>>>>> but I
>>>>>> am pretty sure there will be enough room on the board to add
>>>>>> something
>>>>>> if we need to in a future version. Of course if the ADC voltage
>>>>>> scale is
>>>>>> made nonlinear the FPGA will also have to transform it back (with
>>>>>> more
>>>>>> bits) to linear form before integrating the charge, etc. But this
>>>>>> should
>>>>>> be feasible.
>>>>>> Asking for only a factor of 20 in dynamic range sounds low,
>>>>>> but I'll
>>>>>> wait to hear details at the meeting...
>>>>>>
>>>>>> Gerard
>>>>>>
>>>>>> Curtis A. Meyer wrote:
>>>>>>> Hi Everyone -
>>>>>>>
>>>>>>> there will be a combined tracking meeting on Monday July 28 at
>>>>>>> 1:30pm. I have created the Wiki page and put a couple of items
>>>>>>> on the agenda. Please add appropriate items as people see
>>>>>>> fit.
>>>>>>>
>>>>>>> - Curtis
>>>>>
>>>>>
>>>>> --
>>>>> Professor Curtis A. Meyer Department of Physics
>>>>> Phone: (412) 268-2745 Carnegie Mellon University
>>>>> Fax: (412) 681-0648 Pittsburgh PA 15213-3890
>>>>> cmeyer@ernest.phys.cmu.edu http://www.curtismeyer.com/
>>>>>
>>>>
>>>> ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
>>>> ) `\ -
>>>> / '. | +
>>>> | `, Elke-Caroline Aschenauer =
>>>> \,_ `-/ -
>>>> ,&&&&&V Jefferson Lab +
>>>> ,&&&&&&&&: HALL-D 12C / F381 121-A Atlantic Avenue =
>>>> ,&&&&&&&&&&; Suite 8 Hampton, VA 23664 -
>>>> | |&&&&&&&;\ 12000 Jefferson Ave +
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>>>> | | ;--' | Mail: elke@jlab.org Mobil: 001-757-256-5224 -
>>>> '--' `-.--. | +
>>>> \_ | |---' Tel.:
>>>> 001-757-269-5352 =
>>>> `-._\__/ Fax.:
>>>> 001-757-269-6331 -
>>>>
>>>> +=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+
>
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