Subject: Re: Noise directory
From: Craig McMurtry <[email-masked]>
To: Bill Forrest <[email-masked]>
Cc: [email-masked], Rob Simcoe <[email-masked]>
Date: Thu, 27 Aug 2009 19:04:25 -0400

Hi Rob,

I've finished writing code to use the reference pixels to correct for
drifts.  Here is a graph of the read noise for CDS taken with
Christoph's software.  We took 32 identical CDS images at G=11.3
(1.24e-/ADU) and then processed them temporally, i.e. per pixel noise.

The peak of the distribution is 16.1 e-, but there is a tail which is
due to the strangely higher noise in every other output.  I created a
FITS file where the pixel values are the read noise in ADU.  That FITS
file is large (32MB), so I don't think I can email it.  

Bill - perhaps you can put it in your web directory?  It is located at:
/home/craig/detectors/FIRE/H2RG-160-acqarray/noise
+SIDECAR/readnoise_temporal_Fowler-1.fits
When you look at the FITS image, you might notice that both the low
noise and high noise outputs have about half (37/27 cols) where part is
higher and part is lower.  The outputs are read such that the 1st is
read left to right, while the 2nd is read right to left, and repeats for
all 32 outputs.  Recall that each output reads across the row (64
columns) and not down the column.  So, whatever is giving higher noise
for the first 37 columns read on each output and then lower noise on the
remaining 27 columns is probably related to some clock feed through.  If
this excess noise can be eliminated, then I would guess the real read
noise would be around 12 e- per pixel. 

Cheers,
Craig

On Thu, 2009-08-27 at 17:13 -0400, Bill Forrest wrote:
> Hi Rob,
> 
> Using 3.5 e-/ADU at gx4 and 1.24 e-/ADU at gx11.3, here is the full sequence of
> CDS measurements all with Vref1 = 1.75 V on V3, InPcommon on V1, VrefMain on V4.
> http://astro.pas.rochester.edu/~forrest/SidecarASIC
> 
> time	gain	VrefMai	ADU	p-p ADU	RMS e-
> ----	----	-----	---	----	-----
> 	Detector noise, V2 connected to InPadP
> 113534	4	1.44		15	10.5
> 	System noise, InPCommon on V2
> 141803	11.3	1.70	railed at 65,536 ADU, no good
> 142032	4	1.70	33,000	12	8
> 142841	4	1.75	1000, too low, too close to zero
> 142953	11.3	1.75	1000, too low, too close to zero
> 143232	11.3	1.725	35,000	15	4	wow! really low system noise!
> 	Detector noise, V2 back to InPadP
> 144444	11.3	1.44	26,000	36	9	
> This is considerably lower than Craig's 17 e-, ???
> 	Connect pump electrically and mechanically
> 150604	11.3	1.44	28,000	250	63	large pump noise
> 	Connect pump mechanically but not electrically
> 150938	11.3	1.44		<50		noise from electrical connection
> 
> Bill
>