[Halld-tracking-hw] FDC meeting minutes posted
Fernando J. Barbosa
barbosa at jlab.org
Mon Sep 20 16:24:13 EDT 2010
Hi Naomi,
The dynamic range in GlueX-doc-1364 is at the input and in fC, not mV.
For your configuration, the preamp differential output amplitude is 380
fC x 0.57 mV/fC = 216.6 mV (5% linearity).
Best regards,
Fernando
Naomi Jarvis wrote:
>
> Hi Fernando and Gerard,
>
>
> We are very happy with the 550mV fADC range, preamp and HVB
> combination that we now have here at CMU. We were under the
> impression that the final fADC range was to be 0.5V.
>
> Gluex doc 1364 shows our preamp as having 380mV dynamic range; at that
> point it is 5% non-linear, saturation is very approximately 520mV.
> At present the pedestal requires ~25mV. I believe we can correct
> off-line for the preamp performance some way after passing the 5%
> non-linear mark at 380mV towards 520mV.
>
> Assuming the big CDC will initially be noisier, I would like to allow
> 50mV for its pedestal; then if this can be reduced we will have a
> happy increase in range.
>
> Would it be possible to give us a fADC range of 50mV (for pedestal) +
> 520mV preamp saturation point = 570mV?
>
>
> (Can you define the 520mV point more accurately? I obtained this from
> amplitude spectra, from the scope it looks more like 560mV.)
>
>
> Best regards,
>
> Naomi.
>
>
>
>
>
> On Sep 17, 2010, at 12:13 PM, Curtis A. Meyer wrote:
>
>> Hi Fernando -
>>
>> We worked hard to get the dynamic range that we needed in the CDC
>> and I am
>> not willing to give it up now. With regard to the peaking time, we
>> have always stated
>> that in the CDC, we need 3-5 samples on the leading edge. This is
>> 24-40ns rise time.
>> In the current setup, we have the shaper in front of the Flash ADC.
>> We are under the
>> impression that this is built into the new flash ADC. That said, the
>> 35ns peaking time
>> seems reasonable to us.
>>
>> Curtis
>> On 9/17/10 10:57 AM, Fernando J. Barbosa wrote:
>>> Hi Gerard and Lubomir,
>>>
>>> The peaking time with the preamp and 18 m of cable is 14 ns and so
>>> it is the minimum one can achieve. I agree that 25 ns would be the
>>> minimum in trying to get three samples on the leading edge for
>>> timing interpolation. On the other hand, a 35 ns peaking time is
>>> very reasonable so we are perhaps considering optimizing this
>>> between 25 ns and 35 ns and based on the benefits of noise shaping.
>>> I don't think Lubomir included the time walk correction but this can
>>> be found on GlueX-doc-1364 for the ASIC (GAS-II).
>>>
>>> Regarding the assembly variants, I agree with Eugene that we should
>>> try to get one fADC125 but we need to consider this carefully. We
>>> have considered two fADC125 assembly versions, one for the CDC (low
>>> gain preamp) and the other for the FDC strips (high gain preamp)
>>> primarily based on fully using the ADC dynamic range. The preamp
>>> output ranges (@ saturation) are not the same in the configurations
>>> we are using: 430 mV for high gain and 330 mV for low gain. If we
>>> set the ADC full scale (FS) at 430 mV (4095 on 12-bit), then 330 mV
>>> will be at 76% FS (3100 on 12-bit). Are we willing to sacrifice 25%
>>> of the ADC range on the CDC in exchange for one fADC125 version
>>> (based on saturation conditions)?
>>>
>>> However, there is another issue to consider if we are to have a
>>> single ADC. The output saturation at 430 mV is way out of the linear
>>> range and the output is 285 mV @ 5% linearity. For the CDC and the FDC:
>>>
>>> CDC - 330 mV @ Saturation, 207 mV @ 5% linearity
>>> FDC Strips - 430 mV @ Saturation, 285 mV @ 5% linearity
>>>
>>> For a single ADC solution, I propose we set the ADC FS at 380 mV. We
>>> can set this even lower for a tighter linear range of interest.
>>>
>>> Best regards,
>>> Fernando
>>>
>>>
>>>
>>>
>>>
>>> Gerard Visser wrote:
>>>> Hi Lubomir,
>>>> We should perhaps discuss the shaping option ideas more fully
>>>> in the next meeting, I can call in. I didn't realize this was on
>>>> the agenda today.
>>>> In my opinion it is *feasible* to support two different
>>>> versions of the module with different shaping time. This amounts
>>>> only to different values for some capacitors, inductors, and
>>>> resistors to be used in assembly. The quantities are large enough
>>>> that there should be no significant cost impact, except for
>>>> probably a larger overall quantity of spares to be built. Of
>>>> course, I agree it is simpler to have only one version.
>>>> Presently the peaking time of the preamp-cable-ADC125 is about
>>>> 35 ns I believe. (Maybe a bit more in the case of the cathodes if
>>>> the detector capacitance affects it; it would make sense but I
>>>> don't know really.) We might try to reduce it but 14 ns seems to me
>>>> too small - there will be too much amplitude above the Nyquist
>>>> zone, this has to degrade timing at some point. Maybe some
>>>> compromise value like 25 ns would be better to try.
>>>> Anyway the starting point for this should probably be to remove
>>>> all explicit shaping from a channel, hook it up w/ preamp and cable
>>>> and a test pulser and input loading capacitor, and see the pulse
>>>> shape. This will exhibit the minimum achievable peaking time; and
>>>> we can also then we can calculate the shaping time for the ADC
>>>> board to get to the desired overall peaking time.
>>>> Can you describe the algorithm applied to ADC data to get the
>>>> timing measurement for page 514 work? Is there a fit here, or just
>>>> level-crossing using the same threshold e.g. 30mV? Certainly an
>>>> optimal timing algorithm will use more than 2 datapoints from the
>>>> ADC, i.e., is not simply just a level crossing and linear
>>>> interpolation between two points.
>>>> Is the discriminator simulation 'perfect' or does it include
>>>> real-world distortions such as time walk (dispersion)?
>>>> Sincerely,
>>>>
>>>> Gerard
>>>>
>>>>
>>>> Lubomir Pentchev wrote:
>>>>
>>>>> The minutes of the last FDC meeting were posted at:
>>>>>
>>>>> http://www.jlab.org/Hall-D/software/wiki/index.php/Minutes-9-16-2010
>>>>>
>>>>> Regards,
>>>>> Lubomir
>>>>>
>>>> _______________________________________________
>>>> Halld-tracking-hw mailing list
>>>> Halld-tracking-hw at jlab.org
>>>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
>>>>
>>>
>>>
>>> _______________________________________________
>>> Halld-tracking-hw mailing list
>>> Halld-tracking-hw at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
>>
>>
>> --
>> Prof. Curtis A. Meyer Department of Physics
>> Phone: (412) 268-2745 Carnegie Mellon University
>> Fax: (412) 681-0648 Pittsburgh PA 15213-3890
>> cmeyer at ernest.phys.cmu.edu http://www.curtismeyer.com/
>>
>>
>> _______________________________________________
>> Halld-tracking-hw mailing list
>> Halld-tracking-hw at jlab.org <mailto:Halld-tracking-hw at jlab.org>
>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: barbosa.vcf
Type: text/x-vcard
Size: 188 bytes
Desc: not available
Url : https://mailman.jlab.org/pipermail/halld-tracking-hw/attachments/20100920/1c262433/attachment.vcf
More information about the Halld-tracking-hw
mailing list