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Entry  Fri Feb 14 02:09:55 2014, ericq, Update, Electronics, Transmon QPD whitening qpdWhitening.pdf
    Reply  Mon Feb 17 20:35:19 2014, ericq, Update, Electronics, Transmon QPD whitening qpdY2whit.pdfETMY_QPD_whitening.zip
       Reply  Tue Jul 8 22:53:02 2014, Jenne, Rana, Update, Electronics, Transmon QPD / whitening 
Message ID: 9637     Entry time: Fri Feb 14 02:09:55 2014     Reply to this: 9642
Author: ericq 
Type: Update 
Category: Electronics 
Subject: Transmon QPD whitening 

 [Quick post, will follow up with further detail later. Excuse my sleepy ELOG writing]

Goal: Check out the transmon QPD signal chain; see if whitening works. Assess noise for 1/sqrt(TRX/Y) use. 

First impression: Whitening would not switch on when toggling the de-whitening. The front monitors on the whitening boards are misleading; they are taken a few stages before the real output. ADC noise was by far the limiting noise source. 

I updated the binary logic in the c1scx and c1scy to actually make the binary IO module output some bits. 

After consulting a secret wiring diagram on the wiki, not linked on the rack information page (here), I worked out which bits correspond to the bypass switches in the whitening board ( a fairly modified D990399, with some notes here)

Now, FM1 and FM2 (dewhitening filters on the ETM QPD quadrants) trigger the corresponding whitening in the boards. Here's a quick TF I took of the quadrant 1 board at ETMY. (I should take a whitening+dewhitening TF too, and post it here...)

qpdWhitening.pdf

Seems to roughly work. Some features may be due to non-accounted for elements in the anti-imaging of the DAC channels I used for the excitation, or such things. The board likely needs some attention, and at least a survey of what is there. 

I also need to take dark noise data, and convert into the equivalent displacement noise in the 1/sqrt(TRX/Y) error signals. For the no-whitening ADC noise, I estimated ~1pm RMS noise on a 38pm linewidth of PRFPMI arms. 

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