[Halld-tracking-hw] Preamps

Thu Jun 10 20:48:30 EDT 2010

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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