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Message ID: 14709     Entry time: Sun Jun 30 19:47:09 2019
Author: rana 
Type: Update 
Category: IOO 
Subject: IMC WFS agenda 

we are thinking of doing a sprucing up of the input mode cleaner WFS (sensors + electronics + feedback loops)

  1. WFS Heads
    1. it has been known since ~2002 that the RF circuits in the heads oscillate. 
    2. in the attached PDF you can see that 2 opamps (U3 & U4; MAX4106) are used to amplify the tank circuit made up of the photodiode capacitance and L6.
    3. due to poor PCB layout (the output of U4 runs close to the input of U3) the opamps oscillate if the if the Reed relay (RY2) is left open (not attenuating)
    4. we need to remove/disable the relay
    5. also remove U3 for each quadrant so that it has a fixed gain of (TBD) and a 50 Ohm output
    6. also check that all the resonances are tuned to 1f, 2f, & 3f respectively
  2. Demod boards
  3. DC quadrant readouts
  4. Whitening
  5. Noise budget of sensors, including electronics chain
  6. diagonalization of sensors / actuators
  7. Requirements -
  8. Optical Layout
  9. What does the future hold ?

  1. what is our preferred pin-for-pin replacement for the MAX4106/MAX4107? internet suggests AD9632. Anyone have any experience with it? The Rabbott uses LMH6642 in the aLIGO WFSs. It has a lower slew rate than 9632, but they both have the same distortion of ~ -60 dB for 29.5 MHz.
  2. the whole DC current readout is weird. Should have a load resistor and go into the + input of the opamp, so as to decouple it from the RF stuff. Also why such a fast part? Should have used a OP27 equivalent or LT1124.
  3. LEMO connectors for RF are bad. Wonder if we could remove them and put SMA panel mount on there.
  4. as usual, makes me feel like replacing with better heads...and downstream electronics...
Attachment 1: WFS-Head.pdf  106 kB  Uploaded Sun Jun 30 21:28:04 2019  | Hide | Hide all
WFS-Head.pdf
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