[Halld-tracking-hw] HVB - FINAL VERSION - and fADC

[Curtis A. Meyer]

Hi Fernando -

  sorry if you assumed that the previous results were based on the 125 
FADC, we did not have
one in our possession until LONG after we had to provide you with the 
ASIC information.

   The first thing that came to mind was to change the resistors in the 
divider network on the
HVB for the CDC.  If instead of dividing by two, we pass 90% of the 
voltage, we would appear
to be in the right range, however, I then remembered that the factor of 
two was based on the
output of the ASIC being in the 0V to 0.5V range, and this would push 
much of our signal in the
extreme non-linear range above 0.5V This is probably not a good solution!

     We set the output of the HVB to match the maximum
(1/2 volt) output of the ASIC, and this was then mapped into the Struck 
FADCs range (the only FADC
we had at the time). Thus, our information is based on having the CDC 
output match the 0 to 1/2
volt output of the ASIC.  The question I have relates to what input the 
FADC-125 accepts? Is it
the 0-1/2 volt from the ASIC, or is it 0 to 1V?

    I guess we do not understand what the FADC-125 is doing, and thus it 
is extremely hard
for us to provide sensible answers. All we know is that with the struck 
system that we had,
we had a system that provided a dynamic range that we could live with. 
With the 125, it
(at least for now) appears that we might have lost some dynamic range.

    While this will fix the level of the cosmic signals where we wanted 
it for our dynamic range,
it again opens the question of what this dynamic range may be with the 
new FADC in conjunction
with the ASIC. Does the input of the FADC-125 match the 0V to 0.5V 
output of the ASIC, or
is it something else?

    Curtis


On 4/11/11 9:29 PM, Fernando J. Barbosa wrote:
> Hi Curtis,
>
> My understanding was that your previous results were obtained with the 
> fADC125. The Struck ADC does not have any shaping to speak of (other 
> than the resulting convolution of the input pulse with its response) 
> so it does not provide for a direct comparison of results.
>
> The fADC125's dynamic range or "gain" cannot be adjusted via firmware 
> to make full use of its dynamic range but requires changing a number 
> of resistors and capacitors per channel (I believe a total of 2 of 
> each). Is this correct, Gerard?
>
> Changing these components is time consuming (72 channels) but should 
> be done for testing the full readout chain prior to committing to the 
> final assembly version. My concern is that this change may be 
> incompatible with the FDC requirements, necessitating two assembly 
> versions (OK), and will impact the procurement schedules. I believe 
> that the FDC can accommodate a change in the dynamic range but perhaps 
> not to the magnitude needed by the CDC. Correct, Lubomir?
>
> We need to discuss these issues at an upcoming tracking meeting with 
> the CDC and the FDC groups and Gerard.
>
> Another topic that Gerard mentioned to me recently and that needs 
> checking is the buffer size.
>
> Best regards,
> Fernando
>
>
>
>
> Curtis A. Meyer wrote:
>> Hi Fernando
>>
>>    the Struck FADC with the modified HVB is fine. It appears that the 
>> FADC125
>> has a factor of two lower gain than the Struck. Perhaps there is a 
>> way to adjust this
>> in the firmware. Our original conclusions based on the data that we 
>> collected
>> with the old struck are still valid, the factor of two is between the 
>> two FADCs
>> which has caught us a little by surprise.
>>
>>   Curtis
>> On 4/11/11 5:43 PM, Fernando J. Barbosa wrote:
>>> Hi Naomi,
>>>
>>> The gain was halved from the original on the modified HVB to fit the 
>>> amplitudes within the fADC range. From your histograms, it seems 
>>> that you need to double the range of the fADC with the original HVB. 
>>> Correct?
>>>
>>> What caused the dramatic change? Gas? Leaks?
>>>
>>> Certainly we need to discuss this as there will most likely be an 
>>> impact on the FDC, if we are to have one fADC for both the CDC and 
>>> the FDC.
>>>
>>> Best regards,
>>> Fernando
>>>
>>>
>>>
>>>
>>> Naomi Jarvis wrote:
>>>> Hi Fernando and Gerard,
>>>>
>>>> I have some results with cosmics and the new fADC online here: 
>>>> http://www.jlab.org/Hall-D/software/wiki/index.php/New_fADC_with_cosmics 
>>>>
>>>>
>>>> This is still a work in progress, we can see (top row of 
>>>> histograms) that the gain in the new fADC is about 1/2 of that of 
>>>> the Struck fADC (&shaper).
>>>>
>>>> Is it possible to change the full scale range of the new fADC?
>>>>
>>>> >From previous work with the Struck fADCs, we know that the preamp 
>>>> output saturates at approx 0.5V (measured after the shaper), so we 
>>>> would only be using half the range of the ADC if we use the 
>>>> unmodified HVB.
>>>>
>>>> We would like to put this on the agenda for the tracking meeting on 
>>>> Wednesday.
>>>>
>>>> Naomi and Curtis.
>>>>
>>>>
>>>>
>>>> On Apr 8, 2011, at 1:38 PM, Fernando J. Barbosa wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I have attached a few drawings of the final HVB. Changes from the 
>>>>> first version are as follows:
>>>>>
>>>>> - signal attenuation network added to each signal (back of the PCB)
>>>>> - location and footprint of brackets
>>>>> - channel numbering order to agree with fADC125 (0 through 23) 
>>>>> (top carries the preamp card - see HVB_FINAL_TOP_SILK.PDF).
>>>>> - a few minor dimensional and cosmetic improvements.
>>>>>
>>>>> I have reviewed these changes with Slava but please take a look 
>>>>> and let me know if you have any questions as I plan to start 
>>>>> procurements next week.
>>>>>
>>>>> Thanks and best regards,
>>>>> Fernando
>>>>> <HVB_FINAL_TOP_SILK.pdf><HVB_FINAL.pdf><HVB_FINAL_BOT_SILK.pdf><barbosa.vcf> 
>>>>>
>>>>
>>
>>


-- 
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/