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Entry  Mon Jan 24 18:13:20 2011, Zach, Electronics, GYRO, PDH servo basic_design.png
    Reply  Tue Jan 25 00:05:57 2011, Koji, Electronics, GYRO, PDH servo 
       Reply  Tue Jan 25 01:30:01 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
          Reply  Tue Jan 25 01:39:00 2011, Koji, Electronics, GYRO, PDH servo 
             Reply  Tue Jan 25 02:09:16 2011, Zach, Electronics, GYRO, PDH servo 
                Reply  Tue Jan 25 02:18:17 2011, Koji, Electronics, GYRO, PDH servo 
                   Reply  Wed Jan 26 01:20:10 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
                      Reply  Wed Jan 26 06:20:03 2011, Koji, Electronics, GYRO, PDH servo 
                         Reply  Wed Jan 26 12:42:36 2011, Zach, Electronics, GYRO, PDH servo 
                            Reply  Wed Jan 26 18:10:37 2011, rana, Electronics, GYRO, PDH servo 
                               Reply  Wed Jan 26 19:47:42 2011, Zach, Electronics, GYRO, PDH servo PDH2.pdf
                                  Reply  Wed Jan 26 20:01:31 2011, Zach, Electronics, GYRO, PDH servo 
Message ID: 1270     Entry time: Wed Jan 26 06:20:03 2011     In reply to: 1268     Reply to this: 1272
Author: Koji 
Type: Electronics 
Category: GYRO 
Subject: PDH servo 

- LF356 is too slow. GBW is lower than that of OP27 (8MHz). We don't want to have the phase retardation by the opamps.
- LF357 is not unity-gain stable. You have to use it with the gain larger than 5. i.e. this is not for us.
- OPA604 is a good alternative. This is a JFET opamp with vin=10nV/rtHz, GBW=20MHz and made by BurrBrown!

We had an unreasonable behaviour of AD8336. i.e. increasing the gain increased the input reffered noise, though I did not understand what was happened.
I definitely like the linear gain inverter. Maybe with OPA604 in stead of AD829 to avoid possible oscillation?

Quote:

  I have updated the PDH servo schematic to include:

  • LF356's instead of AD829's for the switchable stages. Rich said it was a good idea to have FET input op amps in this case (like on the universal board). The LF356's have a relatively low GBW of 5 MHz. This shouldn't be a problem since we don't use them at high gain, but in any case we can switch to the LF357 which has a GBW of 20 MHz.
  • External compensation capacitors for the AD829's, which we will still use for the input, output, and buffered monitor stages.
  • Buffered monitors before and after the EXC injection (for TF purposes)
  • RF phase shifter with independent +12 supply (not exactly sure why that is there, but that's the way it is on the universal board)
  • LED indicators for
    • +12
    • -12
    • +12a (RF)
    • Boosts 1-4
  • Test points for
    • +12
    • -12
    • +12a
    • +5 (comparator supply)
    • various places around the circuit we might want them

I hope to be able to position all the BNC/SMA/LEDs on one edge of the board so that we can have them sticking out the face of the NIM module. We can use Front Panel Express to make a fancy face.

We still need to talk about the variable gain stage. Koji doesn't like the linear-in-dB unit, so the other alternative is to have an amplifier with a pot in the feedback path. Does anyone else have any feelings for/against this?

PDH2.pdf

 

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