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40m Log |
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Thu Jan 4 12:46:27 2018, gautam, Update, ALS, Fiber ALS assay 
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Thu Jan 11 14:22:40 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 11 20:51:20 2018, gautam, Update, ALS, Fiber ALS assay
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Tue Jan 16 21:50:53 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 18 00:35:00 2018, gautam, Update, ALS, Fiber ALS assay 
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Fri Jan 19 11:34:21 2018, gautam, Update, ALS, Fiber ALS assay
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Fri Jan 19 23:04:11 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 24 00:33:31 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 24 10:45:14 2018, gautam, Update, ALS, Fiber ALS assay
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Thu Jan 25 23:59:14 2018, gautam, Update, ALS, Fiber ALS assay
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Fri Jan 26 20:03:09 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 31 15:45:22 2018, gautam, Update, ALS, Fiber ALS assay
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Wed Jan 31 16:29:42 2018, gautam, Update, ALS, Modulation depths 
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Wed Jan 31 16:33:53 2018, gautam, Update, ALS, ALS electronics at LSC rack
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Wed Jan 31 22:32:11 2018, gautam, Update, ALS, ALS signal chain + power budget 
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Thu Feb 1 01:24:56 2018, gautam, Update, ALS, D0902745 revamp underway
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Fri Feb 2 00:26:34 2018, gautam, Update, ALS, D0902745 revamp underway
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Fri Feb 2 13:16:55 2018, gautam, Update, ALS, ALS signals whitening switching 
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Mon Feb 5 14:11:01 2018, gautam, Update, ALS, Huge harmonics in ALS channels 
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Mon Feb 5 22:57:28 2018, gautam, Update, ALS, Huge harmonics in ALS channels
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Tue Feb 6 11:13:26 2018, gautam, Update, ALS, Possible source of ground loop identified
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Tue Feb 6 22:55:51 2018, gautam, Update, ALS, Possible source of ground loop identified
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Thu Feb 8 00:33:20 2018, gautam, Update, ALS, D990694 characterization / THD measurement plan
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Thu Feb 8 01:27:16 2018, Koji, Update, ALS, D990694 characterization / THD measurement plan
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Fri Feb 9 13:37:44 2018, gautam, Update, ALS, THD measurement trial
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Thu Feb 8 12:00:09 2018, gautam, Update, ALS, D990694 is NOT differential receiving
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Thu Feb 8 13:13:14 2018, gautam, Update, ALS, D990694 pulled out  
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Thu Feb 8 18:10:36 2018, gautam, Update, ALS, D990694 pulled out
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Wed Feb 7 15:51:15 2018, gautam, Update, ALS, D0902745 revamp complete
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Fri Feb 16 01:34:40 2018, gautam, Update, ALS, D0902745 in-situ testing 
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Tue Feb 20 23:08:27 2018, gautam, Update, ALS, D0902745 in-situ testing
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Thu Feb 22 00:09:11 2018, gautam, Update, ALS, D0902745 in-situ testing  
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Sun Feb 25 00:03:12 2018, gautam, Update, ALS, Daughter board prototyping    
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Mon Feb 26 20:55:56 2018, rana, Update, ALS, Daughter board prototyping
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Tue Feb 27 21:10:45 2018, gautam, Update, ALS, Daughter board testing  
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Wed Feb 28 19:13:25 2018, gautam, Update, ALS, ADC test for differential receiving in c1lsc
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Fri Mar 2 01:45:06 2018, gautam, Update, ALS, new look ALS electronics
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Mon Mar 5 17:27:34 2018, gautam, Update, ALS, new look ALS electronics - characterization
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Thu Mar 8 00:40:25 2018, gautam, Update, ALS, new look ALS electronics - characterization
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Thu Mar 8 19:38:37 2018, gautam, Update, ALS, digital unwhitening of daughter board
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Thu Mar 8 23:50:27 2018, gautam, Update, ALS, First look at new ALS electronics
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Fri Mar 9 01:07:01 2018, gautam, Update, ALS, First look at new ALS electronics
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Mon Mar 12 22:08:31 2018, gautam, Update, ALS, Noisy POX
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Mon Mar 12 23:57:31 2018, gautam, Update, ALS, Noisy POX 
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Mon Mar 19 15:02:29 2018, gautam, Update, ALS, Noisy MC sensing
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Thu Feb 1 15:31:12 2018, gautam, Update, ALS, ALS signal chain + power budget
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Wed Feb 7 10:16:26 2018, gautam, Update, ALS, ALS signal chain + power budget
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Thu Jan 25 13:18:41 2018, gautam, Update, ALS, Fiber ALS assay
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Message ID: 13648
Entry time: Thu Feb 22 00:09:11 2018
In reply to: 13644
Reply to this: 13655
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Author: |
gautam |
Type: |
Update |
Category: |
ALS |
Subject: |
D0902745 in-situ testing |
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I thought a little bit about the design of the preamp we want for the demodulated ALS signals today. The requirements are:
- DC gain that doesn't cause ADC saturation.
- Audio frequency gain that allows the measured beat signal spectrum to be at least 20dB the ADC noise level.
- Electronics noise such that the measured beat signal spectrum is at least 20dB above the input-referred noise of this amplifier.
- Low pass filtering at the input to the differential receiving stages, such that the 2f product from the demodulation doesn't drive the AD829 crazy. For now, I've preserved the second-order inductor based LPF from the original board, but if this proves challenging to get working, we can always just go for a first-order RC LPF. One challenge may be to find a 2.2uH inductor that is compatible with prototype PCB boards...
- Differential sending, since this seems to be definitively the lower noise option compared to the single-ended output (see yesterday's measurement). The plan is to use an aLIGO AA board that has differential receiving and sending, and then connect directly to the differential receiving ADC.
Attachment #3 shows a design I think will work (for now it's a whiteboard sketch, I''ll make this a computer graphic tomorrow). I have basically retained the differential sending and receiving capabilities of the existing Audio I/F amplifier, but have incorporated some whitening gain with a pole at ~150Hz and zero at ~15Hz. I've preserved the DC gain of 10, which seems to have worked well in my tests in the last week or so. Attachments #1 and #2 show the liso modelled characteristics. Liso does not support input-referred noise measurements for differential voltage inputs, so I had to calculate that curve manually - I suspect there is some subtlety I am missing, as if I plot the input referred noise out to higher frequencies, it blows up quite dramatically.
Next step is to actually make a prototype of this. I am wondering if we need a second stage of whitening, as in the current config, we only get 20dB gain at 150Hz relative to DC. Yesterday's beat spectrum measurement shows that we can expect the frequency noise of the ALS signal at ~100Hz to be at the level of ~1uV/rtHz, but this is is around the ADC noise level? If so, 20dB of whitening gain may be sufficient?
Quote: |
Still have to make preamp prototype daughter board with the right whitening shape... This test suggests to me that I should also make the output differential sending...
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*Side note: I was wondering why we need the differential receiving stage, followed by a difference amplifier, and then a differential sending stage. After discussing with Koji, we think this is to suppress any common-mode noise from the mixer outputs. |
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