Re: FADC progress

[René Prieels <R.Prieels@fynu.ucl.ac.be>]

Dear Fred,

We have now to take some decisions.

Let me state the situation.
1) Concerning the need I observe that we will have 2 or 3 neutron 
detectors and as you wish it, 8 channels for the TPC's.
2) Both signals are single ended. The neutron ones are negative and the 
TPC's positive.
3) Only 8 ADCs are still available
4) 2 prototype cards exist : yours with 1 ADC and mine with 2 ADCs
5) On the prototype card, fully differential inputs can make use of the 
full 12 bits ADCs range.
6) As we have only single ended signals, with two different polarities, 
  we can easily use the differential inputs but making use of only the 
half range (11 bits).  For the positive signals we already have a fixed 
bias of 0.3 volt to enlarge the range. For the negative signal this can 
be done with an external negative power supply but the DC level may 
depend on the incoming pulse rate. Moreover the amplitude resolution of 
the neutron detectors may not justify this risk. We could then be 
satisfied with 11 bits for the neutrons.
7) The method for gamma/neutron separation is not yet demonstrated with 
the 175 Mz sampling.
8) The prototype PCB has a several mistakes, that where handily 
corrected, on the two present boards.
9) A new ordering for ADCs to MAXIM company can take a long time

My proposition is the following.
a)  We keep the 2 presently existing prototype boards. This makes 3 
channels available for the 3 neutron detectors.
b)  Since the remaining prototype PCBs, cannot be used directly for the 
TPCs without some modifications,
       since the TPC signals are positive the present prototype input 
design seems adequate,
       since no conceptual errors where found in the prototype board,
       since we just own the ADC components for 8 channels,
       we consequently propose to start directly the design of an 8 
channel card, we the same concept as the prototype one.
       The inputs will be differential, with a possibility to have a 
0.3V bias for positive pulses.
       The negative signals will be converted to 11 bits.
       True differential signals may benefit of 12 bits.
       The front panel will have:
       -  a 20 pin connector (16 differential pins for the 8 single 
ended TPC signals + 2x2 grounds)
       -  the connector for programming the flash memory
       - 8 LEDS connected in pairs to two outputs of each of the 4 
front-end FPGAs.
      The rear of the board will contain:
       -  the ETH connector
       -  the command bus for logic signals

  This could be realized (but not tested) by the very end of October. It 
will be the test version before a mass production.

NOTE:  with 8 channels the throughput will be of course much larger 
then the one of the prototype card.

I need your remarks and benediction before starting.

Today I will send to Claude Petitjean the Louvain prototype board, so 
that you can test it fully with the two input channels
and benefit of your remark during the layout design of the 8 channel 
card.

Best regards
Rene

Le 23-août-05, à 07:08, Frederick Gray a écrit :

>> As I am out of the lab, I can discuss with our technician only on
>> wednesday afternoon... So it can take a while before sending the board
>> by DHL to PSI. But will you have time to play with the board in PSI ?
>
> This trip to PSI may be rather busy, or not.  My primary purpose is 
> just to
> get the muCap DAQ running again.  I also have a few simple slow control
> devices to set up for the muLan run, and I suspect that whatever 
> "spare time"
> is left over will be spent on miscellaneous tasks for muLan.  I should 
> be able
> to make time to set up some basic tests with your board, though.
>
> I think we should make an effort to have at least some of the 
> 8-channel boards
> for the TPC ready for this fall; they could potentially be installed as
> a mid-run upgrade if they aren't ready at the beginning.  I don't know
> whether you've been following the discussion of the "gondola effect" 
> at all,
> but it looks like small signals from electron tracks in the TPC are 
> interfering
> with the muon stop definition, causing a huge bias in the measured 
> lifetime
> because of the mu-e correlation.   Having 12-bit analog data from a 
> significant
> number of TPC channels might be extremely important for understanding 
> the
> effect.
>
> Thanks,
>
> -- Fred
>
> -- Fred Gray / Visiting Postdoctoral Researcher                 --
> -- Department of Physics / University of California, Berkeley   --
> -- fegray@berkeley.edu / phone 510-642-2438 / fax 510-642-9811  --
>
>
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  René PRIEELS                                   Universite Catholique 
de Louvain
  email: R.Prieels@fynu.ucl.ac.be     Departement de Physique / FYNU
  Tel  : ++ 32 (0)10 / 47 32 09             Chemin du cyclotron, 2
  Fax  : ++ 32 (0)10 / 45 21 83            B-1348 Louvain-la-Neuve - 
BELGIUM
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