Subject: Grounding Tests
From: Bill Forrest <[email-masked]>
To: [email-masked]
Cc: Michael Eads <[email-masked]>, Bill Forrest <[email-masked]>, Craig McMurtry <[email-masked]>, Rob Simcoe <[email-masked]>, Christoph Birk <[email-masked]>
Date: Tue, 08 Sep 2009 17:45:36 -0400

Hi Rob,

Since we couldn't get reasonable results varying VBiasGate from the nominal 2.05
V (even though the various test reports used 2.25-2.4 V), we worked on grounding
using the nominal VbiasGate.  We increased Vreset and DSub both by 0.16 V (to
Vreset = 0.3 V), to be on a better place on the gain curve of the unit cell (see
gain curve in Craig's report).  All at gain code 8, gx4, 3.8 e-/ADU, FIRE
Science grade Spectrometer array.

First with our nominal ground.  Floating from our external power supply.  Analog
gnd connected to Digital gnd on Jade board.  Don't know the influence of USB ground.

directory     RMS noise in ADU's for 4 outputs, CDS, 0-511 columns each
---------     ---- ---- ---- ----
162352        6.5   6.5  7.6  6.8

Next, tie dewar case and shield of 'gender bender' from Jade board to dewar to
Earth Gnd (from 3rd wire of our AC power lines, green ground world around).
163644        8.1  7.8  11.3  7.8  -- clearly worse

Repeat nominal
164005        6.7  6.6  7.8  6.9  -- noise can fluctuate by 0.1-0.2 ADU

Disconnect Analog and Digital grounds on Jade board.  Connect Analog ground
to Earth ground
170530        6.9  6.9  7.9  7.1  -- probably worse, definitely not better

Disconnect connection of Analog gnd to Earth gnd.
170908        7.1  6.9  8.0  7.2  -- about the same as 170530

All data posted at WWW site.  It seems our nominal, floating ground, Analog
connected to Digital grounds on Jade board gave the best results in our lab.
Though we could see a bit of 'weaving pattern' noise in the first and third
outputs (not so evident in the 2nd and 4th outputs) which probably indicates
pickup at some (pretty small) level.

Bill