Subject: Guide array Sidecar tests
From: Bill Forrest <[email-masked]>
To: Rob Simcoe <[email-masked]>, judy <[email-masked]>, Craig McMurtry <[email-masked]>, me <[email-masked]>, Christoph Birk <[email-masked]>
Date: Wed, 12 Aug 2009 17:50:51 -0400

Hi Rob,

We have started testing the guide array with the second Sidecar ASIC at LN2.  It
seems to be working fine.  We first measured the PadP (array output) voltage.
It was 1.54 V (rather than 1.60 V for our bare mux).  The InPcommon (reference
for PadP) was about the same as with the bare mux, 1.8 V.

We went to gain code 8 (12 dB, large Cin, gx4) mode for all the measurements.

Then we went into the 32 channel mode and took one image.  The same odd/even
noise pattern was seen as before.  We used your software to analyze noise versus
channel number.  This showed the odd/even pattern.  But I became concerned
because 1) there is a low-frequency wander in the vertical direction which we
disregarded in our peak-to-peak estimates and 2) there is a dark region at the
bottom (first 50 rows) of the array.  Our eyeball estimates of noise in channel
2 (columns 128-191) and 3 (192-255) were about 1.5 to 2 times lower than your
Standard Deviation numbers.  That's what I called you about, I think if we only
measured noise in the central 32 to 64 rows, the noise would be lower.

The peak-peak noise in 32 channel mode seems a bit higher than our bare mux with
the first Sidecar ASIC.

Then we went to 4 output mode.  We noticed a pattern of vertical noise which had
 'beats', large amplitude followed by small amplitude.  A total of about 25
beats in 2048 rows.  The noise is ambiguous,  the large amplitude regions are at
least 2-3 times as noisy as the small amplitude regions.  I was estimating (1 to
2) times 50 p-p, but as low as 25 p-p between beats.

To see if the beats (which I don't think we ever saw before) were in the array
output, or might be grounding, or pickup, or?? we attached InPcommon to both V2
and V1, while keeping VrefMain on V4 and Vref1 on V3.  The noise was remarkably
low, 12.5-15 ADU p-p.  About equal to the A/D noise floor we measured previously
with the lowest gain of x0.7.  No beats whatsoever.

Using Craig's measured e-/uV, we have 3.5 e-/ADU here.  Craig measured 17 e- of
read noise with our black box drive electronics.  The ASIC system noise of 15
ADU p-p is approximately 3 ADU RMS or 11 e-.  The guide array noise of 50 p-p
corresponds to 35 e- of noise.  The 'between beats' noise of 25 p-p amounts to
about 17 e- of read noise.

We don't know where the beats could be coming from, but I think we have to
conquer them to get good read noise.

The data is available at astro.pas.rochester.edu/~forrest/SidecarASIC in the
three directories with dates of 0812 in the order: 32-output, 4-output, preamp
shorted.

Bill