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Entry  Wed Nov 23 17:48:16 2016, rana, koji, Update, IOO, How bad is the McWFS? 
    Reply  Sat Nov 26 19:16:28 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_response.pdfWFS_demod_noise.pdfWFS_demod_noise_plan.pdfScreen_shot_2011-07-01_at_11.13.01_AM.png
       Reply  Tue Nov 29 17:45:06 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis demod.pdfWFS_demod_response.pdfWFS_demod_noise.pdf
          Reply  Tue Nov 29 18:35:32 2016, rana, Update, IOO, IMC WFS Demod board measurement & analysis 
             Reply  Fri Dec 2 18:02:37 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_noise_orig.pdfWFS_demod_noise_mod.pdf
                Reply  Sat Dec 3 13:27:35 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis WFS_demod_noise.pdfdemod.pdf
                   Reply  Tue Dec 6 13:37:02 2016, Koji, Update, IOO, IMC WFS Demod board measurement & analysis demod.pdfWFS_error_noise.pdf
                      Reply  Tue Dec 6 16:47:40 2016, Koji, Update, IOO, IMC WFS whitening filter investigation D990196-C.pdf
                         Reply  Tue Dec 6 17:54:08 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 34.png
                            Reply  Tue Dec 6 22:41:49 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 
                               Reply  Tue Dec 13 17:26:42 2016, Koji, Update, IOO, IMC WFS whitening filter investigation 
                                  Reply  Thu Dec 15 03:46:19 2016, rana, Update, IOO, IMC WFS whitening filter investigation 
Message ID: 12645     Entry time: Tue Nov 29 17:45:06 2016     In reply to: 12641     Reply to this: 12647
Author: Koji 
Type: Update 
Category: IOO 
Subject: IMC WFS Demod board measurement & analysis 

Summary: The demodulator input noise level was improved by a factor of more than 2. This was not as much as we expected from the preamp noise improvement, but is something. If this looks OK, I will implement this modification to all the 16 channels.


The modification shown in Attachment 1 has actually been applied to a channel.

  • The two 1.5uF capacitors between VP and AN/AP were added. This decreases the bandwidth of the demodulator down to 7.4kHz
  • The offset trimming circuit was disabled. i.e. Pin18 of AD831 was grounded.
  • The passive low pass at the demodulator output was removed. (R18, C34)
  • The stage1 (preamp) chip was changed from AD797 to OP27.
  • The gain of the preamp stage was changed from 9 to 21. Also the thin film resistors are used.

Attachment 2 shows the measured and expected output signal transfer of the demodulator. The actual behavior of the demodulator is as expected, and we still keep the over all LPF feature of 3rd order with fc=~1kHz.

Attachment 3 shows the improvement of the noise level with the signal reffered to the demodulator input. The improvement by a factor >2 was observed all over the frequency range. However, this noise level could not be explained by the preamp noise level. Actually this noise below 1kHz is present at the output of the demodulator. (Surprisingly, or as usual, the noise level of the previous preamp configuration was just right at the noise level of the demodulator below 100Hz.) The removal of the offset trimmer circuit contributed to the noise improvement below 0.3Hz.


Attachment 1: demod.pdf  50 kB  | Hide | Hide all
demod.pdf
Attachment 2: WFS_demod_response.pdf  456 kB  | Hide | Hide all
WFS_demod_response.pdf
Attachment 3: WFS_demod_noise.pdf  573 kB  | Hide | Hide all
WFS_demod_noise.pdf
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