Pre-Amplifier Modifications
                    -------------------------------


                                                 Original Rev.  8-SEPT-2006
                                                  Current Rev.  8-SEPT-2006



The intent of this file is to describe the modifications that are
required or contemplated to the D-Zero Run II Dual FET PreAmps for
use in the LArTPC PMB-16 card.  Background material describing the
motivation for each modification and the required parts for each
modification are also presented.


1. FET Input Stage Feedback Network

   As used in D-Zero the feedback FET input stage feedback network is
   a 5 pFd capacitor and a 3 Meg Ohm resistor.  There are two problems
   with this for LArTPC work:

     - The Coulombs to Volts gain is lower than what you want.
       5 pFd feedback implies  0.2 mVolt output per femto Coulomb input.

     - The time constant  5 pFd x 3 Meg = 15 usec  is a little
       shorter than what you want considering the drift time between
       planes in the LArTPC detector.


   ECO  Remove the existing feedback capacitor and resistor.
        Install a parallel  2 pFd and 20 Meg Ohm  feedback network.

   Parts  The 20 Meg Ohm resistor must be a low noise type.
          The 2 pFd capacitor should be a NP0 low loss type.

   The new feedback components must be installed with very short
   leads close to the preamp hybrid substrate.



2. Driver Stage output RC Network

   As used in D-Zero the Driver Stage has a series  10 nFd  115 Ohm
   RC output network.  The 10 nFd capacitor is used for DC blocking
   and to set a low frequency cutoff.  The 115 Ohm resistor is used
   to back terminate the transmission line down to the BLS cards in
   the Platform.  The problem is that the  10 nFd x 115 Ohm = 1.15 usec
   time constant is too short for the LArTPC detector.

   ECO  Jumper over C15 and C24 which are the two 10 nFd capacitors
        in the Driver Stage output network.

   The function of these two capacitors is taken up by components
   on the PMB-16 card itself.  The 115 Ohm series resistors are
   retained to provide some isolation for the Driver Stage and to
   guarantee stability of the PreAmp Driver Stage.  The presence of
   these 115 Ohm series resistors must be taken into consideration
   when calculating the component values for the subsequent PostAmp
   Filter stage on the PMB-16.



3. Driver Stage Input Coupling Capacitor

   The input network to the Driver Stage is a  0.15 uFd  capacitor
   C6 and a  3.3k Ohm  resistor R12.  This time constant is  0.15 uFd
   x 3.3k Ohm = 495 usec.  This is much longer than necessary and
   thus lets excess low frequency noise into the Driver Stage.  We
   could reduce the value of this capacitor to start chopping off
   the low frequency response at a frequency more appropriate for
   the LArTPC work.  A reasonable target is in the 30 to 50 usec
   range for the time constant of this coupling network.

   ECO  Replace C6 at the input to the Driver Stage with a 15 nFd
        capacitor.

   The new capacitor can be installed on the same PreAmp substrate
   layout pattern.



Parts List for all PreAmp ECOs  (per PreAmp)
--------------------------------------------

    1x   2 pFd chip capacitor low loss NP0 type

    1x   20 Meg Ohm resistor  low noise  (metal film is available)

    1x   15 nFd coupling capacitor