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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: 1424     Entry time: Thu May 26 06:28:59 2011     In reply to: 1421     Reply to this: 1425
Author: Frank 
Type: Electronics 
Category: GYRO 
Subject: revised PDH2 schematic 

you've changed the supply from =/-12V to +/-15V. How do you wanna supply it? Using your existing +/-24V supply will create lot's of ground loops as there are no differential inputs or transformer isolated inputs/outputs for the RF stuff.

Quote:

 

 I have made the recommended changes in our email thread and gone through an extra iteration of changes with Koji this afternoon. The current schematic is below.

Changes:

  • The variable gain stage (U7) has been made into a "generic TF stage" à la Sigg MC servo, with the only difference being a trimpot in the feedback path for use as a variable gain stage.
  • Added an AD587KN (low-noise 10-V reference) for the phase shift selection voltage. (To avoid prolonged conversations about one another's bowels, I have made the executive decision to leave the phase shifter on this board and leave the end user the option to forgo it and use cables to trim phase). Using 10V to select, instead of the full 12V, reduces our range from ~250 deg to ~200 deg for most RF frequencies. This should be plenty of room given that we can always adjust cables to get macroscopic shifts.
  • In order to use the AD587, and since there was really no point in NOT doing it, I changed the board supply voltages from +/-12V to +/-15V. This has the added benefit of increasing our range.
  • Added "CLEAD" capacitors in feedback paths of the TF stage AD829s for shunt compensation, as well as in any of the buffers that need them.
  • Turn and face the strange
  • Changed U7 from OPA604 -> AD829. There was confusion about it needing to not be an AD829 that was leftover from when we were using relays for the TF stages. We are 100% 829 now.
  • Changed the output and pre-EXC monitor buffers to unity-gain followers, and changed the FB resistors to 100 per the datasheet recommendation. Changed the input monitor to have gain of 40 and added appropriate shunt compensation
  • Changed the comparator reference voltage resistors to reflect the switch from 12 V to 15 V.
  • Changed the way the remote boost input pull up is done: in the last iteration, with the setting of +5V (0 ohms on the trimpot), there is "zero" impedance from the +5V supply to the remote control input (bad). Now, the pull-up voltage is selected from the middle terminal of a trimpot, with either end terminal connected through a large resistance to +/-15V. This ensures that current gets limited regardless of the setting.
  • Adjusted the boost indicator LED voltages from +15V to +5V. This needed to be different because we are no longer using transistor switches to control relays.
  • Changed AC coupling capacitors flanking the ERA amp from 1nF -> 10nF per Koji's suggestion, and added a choke inductor (the datasheet says it's optional, but why not trick this thing out?)
  • That's pretty much it, besides some labels for better clarity.

I feel good about the board at this point, so I'm starting on the PCB. Please let me know ASAP if there is a major problem, and send me any minor concerns/comments whenever.

PDH2.pdf

 

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