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Entry  Tue May 24 00:21:31 2011, Zach, Electronics, GYRO, revised PDH2 schematic PDH2.pdf
    Reply  Tue May 24 19:56:08 2011, Zach, Electronics, GYRO, revised PDH2 schematic PDH2.pdf
       Reply  Thu May 26 06:28:59 2011, Frank, Electronics, GYRO, revised PDH2 schematic 
          Reply  Thu May 26 09:17:44 2011, Zach, Electronics, GYRO, revised PDH2 schematic 
             Reply  Fri May 27 10:15:26 2011, Frank, Electronics, GYRO, revised PDH2 schematic 
                Reply  Fri May 27 10:20:47 2011, Zach, Electronics, GYRO, revised PDH2 schematic 
                   Reply  Mon May 30 15:22:22 2011, rana, Electronics, GYRO, revised PDH2 schematic 
                      Reply  Tue May 31 15:59:21 2011, Zach, Electronics, GYRO, revised PDH2 schematic PDH2.pdf
Message ID: 1420     Entry time: Tue May 24 00:21:31 2011     Reply to this: 1421
Author: Zach 
Type: Electronics 
Category: GYRO 
Subject: revised PDH2 schematic 

 I have made most of the suggested changes to the PDH2 schematic. The original comment thread can be found here

What I changed:

  • For the boost control, I switched from using relays (like in the universal box) to Rana and Daniel's favorite, the MAX333A.
  • I used a voltage regulator to get the +5V for the boost control (instead of a divider), to avoid sagging as Koji mentioned.
  • Labelled the individual comparator channel switch voltages for ease.
  • Included a trimmable (-4 to +4 V) pull-up on the boost input so that we can operate it manually if necessary.

What I have not (or not yet) changed:

  • The actual stage gains and TFs. Koji brought up concerns about how some of the stages are attenuating rather than adding gain at some or all frequencies. This is a consequence of our current UGF limit and other unchangeable gains (e.g. the PZT actuator). I chose these values to give us the best noise performance given the dynamic gain we need (filtering), and to avoid excess phase lag of the AD829s. We can revisit this and change the component values, but I wanted to push forward with the PCB.
  • Voltage reference for the phase shifter. As far as I can tell, the error signal is first-order insensitive to phase fluctuations ( V ~ cos(phi) ) when it is optimized, and perhaps that's why there is no reference in the universal servo. Regardless, Frank has indicated that the phase shifter is a bad idea for a specific application anyway. I'm not sure what his objections were, but in any case we need one specific to our particular LO frequency (otherwise it's nearly useless). Maybe it's best to stick to the cable-length-adjustment method, though it is quite handy in the initial stage to have a knob to turn. I think a nice middle-ground is to leave it in and then just disconnect it once the final state is reached.
  • "Extra pads". Rana and Koji have suggested adding extra pads for future tuning of the transfer function, etc. I added them to the first stage before, but I don't have a good grasp of where else someone down the road will wish I had added them. If you have any concrete examples of where I will add them in.

Here is the schematic. As soon as I have fielded some more comments I can move on to redoing the PCB.

PDH2.pdf

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