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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: 1275     Entry time: Wed Jan 26 19:47:42 2011     In reply to: 1274     Reply to this: 1276
Author: Zach 
Type: Electronics 
Category: GYRO 
Subject: PDH servo 

EDIT (ZK): After playing around in LISO for a little bit, I'm fairly convinced that we will have no problem using the OPA604s for the switchable stages. We will want the high-flatband ranges of each of the filter stages to be at a gain of substantially less than unity (say -20 or -40 dB), since we will do most of the amplification at the input AD829 stage. This still allows for 40-60 dB of amplification at 10 Hz per stage with the boost on. In this regime, the phase lag accumulated per OPA604 stage at 300 kHz is less than a degree (when compared to the AD829, which is essentially still ideal in this configuration).

Below is the servo before any of the modifications Rana suggested. I have replaced the LF356s with OPA604s at Koji's suggestion, and I have replaced the linear-in-dB gain stage with another OPA604 with a 100K trimpot in the feedback path.

Regarding Rana's comments:

Using OPA604s instead of LF356s, and considering that we will not be using them with any serious gain (err--except for in the variable gain stage), shouldn't we expect the phase lag to be less than 10 degrees? If you still think this isn't the way to go, then you are suggesting we go with AD829s and MAX333As for the switching? In that case, we can still use the single-channel sequential boost control that I have set up with the comparator, correct? I just think it's nice not to have a different signal channel for every stage since we are likely to only apply them sequentially.

1) & 2) OK

3) I guess I was imagining shifting the LO, not the PD RF. There will be SMA inputs for each on the front of the box and how we connect them to the mixer will be our choice.

Quote:

This seems too hokey to me. Just use the AD829 and the switching techniques that are in the Sigg electronics. Using this relay/LF crap will leave us with a lot of phase lag. The board should have less than 10 deg. of phase lag at 300 kHz.

1) For the regulators, you should use bigger caps in parallel with the little caps. Big means > 50 uF.

2) Since this is quasi generic, you ought to have more pads around the input opamp and some of the others. Look at the layout of the generic stages in the Sigg MC board.

3) For the RF, we don't want to put the PD signal through a noisy phase shifter. The LO signal shoudl be the one getting phase shifted.

 

 PDH2.pdf

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