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(From mitch) [Fwd: Re: Some more preamp questions] (fwd)





Date: Sat, 30 Dec 2006 23:47:35 -0500
From: mitch@hep.upenn.edu
To: Fernando J. Barbosa <barbosa@jlab.org>
Cc: HallD _Tracking_HW <halld-tracking-hw@jlab.org>
Subject: Re: Some more preamp questions

Hi Fernando,
            hope you're enjoying your holidays.  I thought I might
try to get a head start on the new year and try to answer your note.

1) Costs are in line with my expectations.
2) How about adding:  lead 25, 56 = GND
   Also we may opt for simple shape control so 22, 23 would be shape
   control contingency if we get time to add it in.
3) I am not seeing the 50-60% variations on page 23. It looks like we
   should clarify this page and perhaps come up with a table.  One thing
   that may help is to say that the DC offset changes with Vdd.  I assume
   that Vdd will be  fixed during a run and that since you will be
   digitizing the offset values, only difference values  (peak - baseline)
   will be used to calculate the signal amplitude.  My guess on the
   difference values over the 2.4 - 2.6V range is less than 10%.
   While it doesnt appear to be an issue here keep two things in mind when
   considering amplitudes.
    1) Milind is considering only  the charge collected in the first 12ns
       here ( in some cases 7ns) This is ~20% of the total ionization
       charge. The rest of the charge, collected over the several micro
       seconds it takes for the +ions to reach the cathode is cancelled.
    2) The impulse charges we are using represent a worst case charge
       deposition, most of the time charge should be distributed over
       longer time periods with a much less determined shape.

4) Unless there is some differential non linearity between the ranges
shown it seems clear that the difference in amplitude represents a
difference in slope.  We use a 55C junction temperature for normal
simulations. Milind changes this value in spice to do the temperature
sensitivity runs. Note that the linearity at 55C is quite good up to 400fC
for an impulse input.

5) Yes we would only consider multi purpose outputs with the existing
outputs. This is not hard and I would very much like to add a comparator
function. Probably the best thing to do though is to get this prototype
out of the way and see how close it comes to meeting your analog
performance requirements.  I am hoping to get a February MOSIS submission.
When that is out the door we can think about the comparator design. We
will need to discuss funding for that though. I think we have just about
dried up our first allocation. ( If it has in fact made it here.)


                                                           Mitch