[Halld-tracking-hw] Maximum voltage of f125ADC?

Wed May 11 11:05:17 EDT 2011

See http://www.jlab.org/Hall-D/software/wiki/index.php/Newest_preamp#saturation_pics

The preamp saturates before the fADC.  The charge from Fe55 all comes within 160ns; from a track is spread over ~650ns.  To increase our dynamic range, if we want to do that, I think the only options now are to increase the charge division on the HVB, or decrease the HV.   

Naomi.

On May 6, 2011, at 3:58 PM, Beni Zihlmann wrote:

> Hi All,
> let me summarize.
> 1) Fe55 will make a signal of about 370mV and corresponds to
>    about 6keV energy deposition. With the new modified HV board
>    and the new modified preamp board.
> 2) If I assume a mean path length of about 1cm in the straw
>    a 300MeV/c momentum proton will have roughly 10MeV/g/cm
>    energy loss. With a density of 1.78*10^-3 g/cm3 for Argon gas
>    this will give me roughly 17keV energy deposition. not all at one
>    spot like in the case of Fe55. However this is basically 3 times more than Fe55
>    so I can expect a signal up to 3 times higher. in particular if the proton
>    passed through the full 1.6cm tube diameter. For protons of lower
>    energy this will be even more so.
> 
> So now my question:
>    Doesn't this mean that there is a high potential that many low momentum protons
>    will saturate the ADC, or have the potential to saturate the ADC? Because we want
>    to do PID for exactly these low momentum protons shouldn't we rather pay the price
>    of having a lower amplitude output of the amplifier for mips and keep enough headroom
>    at large amplitudes for the low momentum protons?
> 
> any thoughts/comments?
> Beni
> 
> 
>> Hi,
>>    Yes, I was just checking my notes on this and I agree. Of course as noted this is for a narrow pulse not a wide one. The shaping will have a significant effect. Also, this 990mV is measured at the preamp end of the cable and so divides out by the significant loss factor for the cable.
>>    Beni, tell me what you like me to measure (in terms of pulse shape) and I'll set it up.
>>    Sincerely,
>> 
>>        Gerard
>> 
>> On 5/2/2011 11:22 AM, Naomi Jarvis wrote:
>>> From an earlier email - see Gerard's PS.
>>> 
>>> Naomi.
>>> 
>>> 
>>> 
>>> 
>>> Begin forwarded message:
>>> 
>>>> *From: *Gerard Visser <gvisser at indiana.edu <mailto:gvisser at indiana.edu>>
>>>> *Date: *April 13, 2011 3:34:53 PM EDT
>>>> *To: *"Fernando J. Barbosa" <barbosa at jlab.org <mailto:barbosa at jlab.org>>
>>>> *Cc: *GlueX Tracking <tracking at gluex.org <mailto:tracking at gluex.org>>
>>>> *Subject: **Re: [Halld-tracking-hw] Tracking Meting Tomorrow*
>>>> 
>>>> Hi Fernando,
>>>> Thanks, I will change the gain setting as you say.
>>>> Could you please still send me another board in CDC configuration? First of all
>>>> this one is set for cathodes and I might not have enough 0402 jumpers to convert
>>>> to anodes operation, and secondly this board has apparently all channels dead on
>>>> the middle ASIC and I worry perhaps could have an abnormal response on the
>>>> others (I don't know what the cause of the trouble is). In any case, having two
>>>> boards to be able to confirm the measurements on the second unit, I think will
>>>> be a good idea.
>>>> If you have 'plenty' then please also send one in FDC cathode configuration
>>>> (same reasons).
>>>> I have updated my slide with a 2nd one showing the waveforms at the ADC output
>>>> terminals. With the caveat this is as you say for quite the wrong gain selection
>>>> on the ASIC, the results of this test look to me to indicate the linearity is
>>>> really worse than it looks on the ADC125 view, the maximum reasonably linear
>>>> pulse height is about 43% of full scale on the ADC. We'll have to see how this
>>>> looks with the correct gain setting on the ASIC.
>>>> My updated slides are here
>>>> http://npvm.ceem.indiana.edu/~gvisser/GlueX/ADC_scale.pdf
>>>> Sincerely,
>>>> 
>>>> Gerard
>>>> 
>>>> p.s. And the answer to Curtis' question from the other day "Does the input of
>>>> the FADC-125 match the 0V to 0.5V output of the ASIC, or is it something else?":
>>>> For pulses of this shape, the input of the ADC125 matches to an amplitude of
>>>> 990mV, which is indeed probably higher than intended (sorry). HOWEVER care is
>>>> certainly needed - for _wider_ pulses the ADC125 full scale will be _lower_ in
>>>> amplitude (it is a shaper...). [And I presume the CDC can get some pretty wide
>>>> pulses when tracks pass at an angle.]
>>>> 
>>> 
>>> 
>>> 
>>> On May 2, 2011, at 11:13 AM, Beni Zihlmann wrote:
>>> 
>>>> Hi Naomi,
>>>> now I am a bit worried because I was under the assumption that
>>>> the maximum range of the f125ADC is around 500mV.
>>>> Gerard and Fernando can you comment on this? I realize that
>>>> there is some shaping involved but can give an approximate
>>>> value on the maximum Voltage of the f125ADC?
>>>> 
>>>> thanks,
>>>> Beni
>>>>> The fADC range is ~ 1V. That's why Fernando took the terminating resistors
>>>>> off preamp4. Preamp4 saturates at 500mV, preamp5 is ok up to 1V approx.
>>>>> 
>>>>> Naomi.
>>>>> 
>>>>> 
>>>>> 
>>>>> On May 2, 2011, at 8:22 AM, Beni Zihlmann wrote:
>>>>> 
>>>>>> Hi Naomi,
>>>>>> thanks for all the new plots.
>>>>>> I have one more question.
>>>>>> The Fe55 will give roughly 6 keV energy deposition. Do you recall what
>>>>>> the mean energy deposition of a 250 MeV proton is in a straw? The reason
>>>>>> I am asking is that the Fe55 give about 370mV and the F125ADC saturates
>>>>>> around 500mV we have to avoid that the proton will saturate the ADC otherwise
>>>>>> the PID will be very problematic.
>>>>>> 
>>>>>> cheers,
>>>>>> Beni
>>>>>> 
>>>>>> 
>>>>>>> Good morning,
>>>>>>> 
>>>>>>> I just added the scope pics to the wiki, I will get to the rest of item 1
>>>>>>> later on.
>>>>>>> 
>>>>>>> However I can say straight away that the pedestal is at ~ 100 so in each
>>>>>>> case the histo will be bumped up 100. I know from taking the mean of the
>>>>>>> first 100 samples of 100 events that the pedestal standard deviation is
>>>>>>> approx. 6 ADC bins with preamp4 and 12 bins with preamp5 (preamp5=preamp4
>>>>>>> modified) inside the cage.
>>>>>>> 
>>>>>>> 2. Cosmics are very approximately 40mV with preamp4 and 80mV preamp5. See wiki.
>>>>>>> 
>>>>>>> 3. Fe55 amplitudes are ~ 220mV with preamp4 and ~370mV with preamp5.
>>>>>>> 
>>>>>>> The scope pics and amplitudes are at the output of the old shaper unit, so
>>>>>>> they do not correspond exactly to the shaping part of the new fADC.
>>>>>>> 
>>>>>>> 
>>>>>>> Naomi.
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On Apr 27, 2011, at 6:16 PM, Beni Zihlmann wrote:
>>>>>>> 
>>>>>>>> Hi Naomi,
>>>>>>>> in http://www.jlab.org/Hall-D/software/wiki/index.php/Newest_preamp
>>>>>>>> the first two plots are with the old and the new modified preamp card.
>>>>>>>> I assume that these two plots were made with the cosmic trigger setup
>>>>>>>> where you have scintillator paddles above and below the chamber.
>>>>>>>> I hope this is a correct assumption. If yes can you do the following:
>>>>>>>> 
>>>>>>>> 1) make these plots without cutting a way the pedestal and then
>>>>>>>> fit the pedestal width in both cases and also determine the width and
>>>>>>>> position of the minimum ionizing peak in both cases?
>>>>>>>> 
>>>>>>>> 2) on the scope can you see what the mean amplitudes of these signals
>>>>>>>> are for the two cases of preamp cards.
>>>>>>>> 
>>>>>>>> 3) with a Fe55 source what is the signal amplitudes for the two preamp
>>>>>>>> cards.
>>>>>>>> 
>>>>>>>> thanks,
>>>>>>>> Beni
>>>>>>>> 
>>>>>> 
>>>> 
>>>> 
>>> 
> 
> 