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Re: shaper gain




Hi Curtis and Gerard,

Clearly the ADC and the ASIC outputs should match as best as possible. But
my comment is related to the non-linear region, if required, in the
data. The main purpose for the dE/dx measurements is to identify protons
(distinguish them from pions). For this, we simply need to have pulse
height outputs that are different for the two cases, and a non-linear
scale may be fine. In other words, non-linear "corrections" per se may not
be needed, as we are not trying to determine the precise value of energy
loss, simply checking differences between two particle types.

Cheers, Elton.





Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax

On Mon, 28 Jul 2008, Curtis A. Meyer wrote:

> Hi Gerard -
>
>  thanks for the comment on the ADC range. I am not sure what we need to
> do, but it would certainly be better to match as much of the linear range
> of the ASIC to that of the Flash-ADC.  While we can probably correct for
> the lon linear part as we move above the charge limit, I suspect that those
> corrections are probably temperature dependent. While this may not be
> a problem, we probably want to think about this up front.
>
>    Curtis
> On Mon July 28 2008, Gerard Visser wrote:
> > Hi Fernando,
> > 	Oh, one other point, and this is maybe worthwhile for others to
> > consider too. The present "anode" setup of the shaper board, I believe,
> > puts the full scale of the ADC at roughly 770 fC (instantaneous input
> > charge, e.g. Fe55), as documented on page 2 of
> > http://argus.phys.uregina.ca/gluex/DocDB/0007/000736/003/Receiver_Shaper_Setup_for_GPC01.pdf
> > 	In other words, the "good linear range" of the ASIC is presently about
> > 39 to 52% of the ADC range, depending on what you call "good".
> > 	With the proposed change, the "good linear range" of the ASIC should
> > then be about 8 to 10 % of the ADC range. I'm not sure this is really
> > what we want to do... (Although of course we can try it and see. I could
> > be proved wrong!)
> >
> > 	Gerard
> >
> > Gerard Visser wrote:
> > > Hi Fernando,
> > >         Ok, just to check, this will be setting the gain 1/5 of the present
> > > "anode" shaper gain, is that correct? (If not, please say...)
> > ...
> >
>
>
>
> --
> Professor Curtis A. Meyer        Department of Physics
> Phone:  (412) 268-2745          Carnegie Mellon University
> Fax:    (412) 681-0648            Pittsburgh PA 15213-3890
> cmeyer@ernest.phys.cmu.edu  http://www.curtismeyer.com/
>