From: Jordan Nash [Jordan.Nash@cern.ch]
Sent: 31 March 2004 16:47
To: Marc Dejardin
Cc: d.cockerill@rl.ac.uk; Philippe Bloch; Chris Seez

Categories: CERN SpamKiller Note: -50

Dear All,
  I attach a quick calculation of what we should expect for the noise
using the unmodified VFE cards with the VPTs.  As a comparison I also
attach the noise calculation for the modified VFE.

The assumptions I make are
1) The VPT gives a net 28.5 pe/MeV
2) 10.5 Bits for the ADC
3) In the case of the unmodified VFE
   FS charge is 60 pC
   noise of MGPA is 7000 electrons (slightly less than for APD due to
less capacitance)
4) In the case of the modified VFE
   FS charge is 16 pC
   noise of the MGPA is 3050 electrons


For the VFEs we have now, we would then expect a net noise of about
330Mev in the Times 12 with a full scale readout of 1 TeV in the Times
12, and an LSB of 267 MeV.

For modified VFEs, we would have a noise of 120 MeV with a full scale of
292 GeV and an LSB of 72 MeV.

Given the way the current housings are made for these VFEs, it would be
quite difficult to modify them for EE, so we should verify that the
above noise will be alright for measurements irradiating with 120 GeV
electrons.

Let me know if I have made any obvious mistakes,
Cheers
Jordan

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