[Halld-tracking-hw] Preamps
Fernando J. Barbosa
barbosa at jlab.org
Thu Jun 10 22:31:33 EDT 2010
Hi Curtis,
Sorry, I had a mistake in my previous email:
Old preamp - 1.5 mV/fC, 270 fC 1% DR
New Preamp (present CDC configuration) - 0.57 mV/fC, 380 fC 5% DR.
The old preamp saturated most of the time and an interposer was modified
to decrease in half the input charge to the old preamp. That worked!
GlueX-doc-1079 recommends that the new preamp should have a gain of 3
lower than the old preamp to provide some headroom (compared to a gain
of 2 lower).
The noise of the new preamp is much lower than the old preamp as a
function of the input capacitance and the intrinsic S/N has improved. If
we map 380 fC to 4095 channels on the fADC125, a dynamic range of 80
would require a pedestal below channel 50. Noise pick-up should always
be minimized by proper grounding, shielding and minimizing the
connection lengths at the inputs, of course.
I think we have succeeded in meeting the CDC requirements regarding the
ASIC.
Best regards,
Fernando
Curtis A. Meyer wrote:
> Hi Fernando
>
> the point of lowering the gain was to increase the dynamic range so
> we could accommodate
> a larger range of pulse heights (which was crucial for dE/dx). Based
> on the noise that we were
> seeing, we carefully worked out that given the same noise and maximum
> signal size,
> that a gain of 3 to 5 lower would allow us to do dE/dx except for the
> extremely slow protons.
> If the maximum has actually decreased by a factor of two, then we have
> effectively lost that
> in the dynamic range and I think that we probably have a problem with
> this configuration.
>
> Curtis
>
>
>
>
> On 6/10/10 8:24 PM, Fernando J. Barbosa wrote:
>> Hi Naomi,
>>
>> Now it makes sense. The original preamp had a gain of 1.5 mV/fC and
>> the new one that you have is 0.57 mV/fC. So, a factor of 2.63 lower
>> now. This seems to be confirmed on the first set of plots if you were
>> to cut the "overflows" from the left plot (just by looking at the plot).
>>
>> The dynamic range on the old preamp was wider with 400 fC at the 1%
>> level; the new preamp is at 380 fC @ 5% (for your configuration). The
>> older preamp had a much wider DR with a smooth roll off before hard
>> saturation; the new preamp has narrower DR before hard saturation.
>> It is important to keep in mind that we want to operate in the linear
>> region, perhaps even better than the 5% level. This is seen on the
>> next sets of plots for the new preamp has a hard saturation at ~2100
>> channels. The fADC125 will be optimized to have this mapped to the
>> upper level of its 12-bit range.
>>
>> I cannot say much about the energy plots because of non-linearity and
>> saturation on both old and new preamps. The detector gain is too high
>> and I suggest that you take additional runs starting at 1750V.
>>
>> Thanks and best regards,
>> Fernando
>>
>>
>>
>>
>> Naomi Jarvis wrote:
>>>
>>> Hello,
>>>
>>> I just wanted to correct something I wrote yesterday (which did not
>>> make sense anyway). From looking at the scope traces with the 55Fe
>>> source I thought that the new preamp gain was less than that of the
>>> old preamp. After actually collecting data and extracting amplitude
>>> histograms it turned out that the preamp output was in fact
>>> saturating, although I could not see this on the scope. I thought I
>>> could distinguish between saturated and non-saturated traces, but
>>> evidently this was not the case. So I have added some 55Fe plots
>>> to the wiki:
>>>
>>> http://www.jlab.org/Hall-D/software/wiki/index.php/Preamp_4:_Comparison_of_55Fe_data_with_original_preamp
>>>
>>>
>>> These are again comparing the two preamps, and to be clear, the only
>>> difference between the two sets of runs is that the preamps are
>>> switched and the baseline on the shaper is set to approx -130mV
>>> (because the preamps have a different baseline). Everything else is
>>> the same, both sets of data were taken on the same day.
>>>
>>> Is there anything else you would like me to try with it tomorrow, or
>>> leave counting over the weekend?
>>> Naomi.
>>>
>>>
>>>
>>> Fernando J. Barbosa wrote:
>>>> Hi all,
>>>>
>>>> It seems that Monday @ 10 is preferable to most.
>>>>
>>>> Gerard, I will discuss with you any issues related to the preamps
>>>> and ASICs afterwards.
>>>>
>>>> In preparation for the meeting, I suggest reviewing GlueX docs
>>>> 1070, 1079 and 1364. I will send an email with the agenda for the
>>>> meeting by the end of the week.
>>>>
>>>> Thanks and best regards,
>>>> Fernando
>>>>
>>>> Curtis A. Meyer wrote:
>>>>> Monday at 10:00am would be great! Curtis
>>>>> On 6/9/10 2:31 PM, Fernando J. Barbosa wrote:
>>>>>> Hi Curtis,
>>>>>>
>>>>>> Would Monday @ 10 next week work for everyone?
>>>>>>
>>>>>> Best regards,
>>>>>> Fernando
>>>>>>
>>>>>>
>>>>>>
>>>>>> Curtis A. Meyer wrote:
>>>>>>> Hi Fernando
>>>>>>>
>>>>>>> the next tracking meeting is not until June 23, so if we wait
>>>>>>> until then to discuss this
>>>>>>> issue, we will certainly fail to meet your deadline of June 25.
>>>>>>> It also takes several days
>>>>>>> of cosmic running to get a data point, so checking anything also
>>>>>>> takes time. If there is any
>>>>>>> way that we could have a meeting next week, it would help speed
>>>>>>> things along.
>>>>>>>
>>>>>>> thanks - Curtis
>>>>>>>
>>>>>>>
>>>>>>> On 6/9/10 12:55 PM, Fernando J. Barbosa wrote:
>>>>>>>> Hi Naomi,
>>>>>>>>
>>>>>>>> I suggest we reserve part of the next tracking meeting to
>>>>>>>> discuss these issues.
>>>>>>>>
>>>>>>>> Let me also take the opportunity to emphasize that the CDC and
>>>>>>>> the FDC groups must finalize their measurements so that the
>>>>>>>> procurement of the ASICs is not impacted. This means that I
>>>>>>>> would like to close this project by 25 June 2010.
>>>>>>>>
>>>>>>>> Thanks and best regards,
>>>>>>>> Fernando
>>>>>>>>
>>>>>>>>
>>>>>>>> Naomi Jarvis wrote:
>>>>>>>>>
>>>>>>>>> Good morning!
>>>>>>>>>
>>>>>>>>> I would like to talk about the new preamp but I don't think
>>>>>>>>> there will be enough time in our tracking mtg this morning.
>>>>>>>>> The concerns are that the preamp output is topping out at
>>>>>>>>> around 500 mV even with the cosmics, and the gain for cosmics
>>>>>>>>> seems to have increased, whereas for Fe55 it was ~1/3 less.
>>>>>>>>>
>>>>>>>>> I put one page on the wiki
>>>>>>>>> http://www.jlab.org/Hall-D/software/wiki/index.php/CDC#Preamp4_.28GlueXdoc1364_Tbl_2_Row_2.29
>>>>>>>>>
>>>>>>>>> The recent cosmic runs there took a week each, and were with
>>>>>>>>> the chamber flat, ie 90 degree cosmics. I'll add more data
>>>>>>>>> as it becomes available; at present it is counting at 2kV.
>>>>>>>>> Can we set up a time to talk about this next week? (The rest
>>>>>>>>> of this week is out for us; I think the only times we cannot
>>>>>>>>> do next week are 1pm Tues + the regular mtg on Wed).
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Naomi.
>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>
>>
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>
>
> --
> 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/
>
>
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