40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
 List  |  Find  |  Login  |  Help 
Entry  Mon Dec 2 00:27:20 2019, gautam, Update, ALS, Green ALS resurrection ALSnoiseComparison.pdfALS_TR_RIN.pdfGreemAM.pdf
    Reply  Mon Dec 2 18:20:29 2019, gautam, Update, ALS, EY uPDH post mixer LPF EY_uPDH_LPF.pdfEY_uPDH_OLTF.pdf
       Reply  Mon Dec 2 20:18:18 2019, rana, Update, ALS, EY uPDH post mixer LPF 
          Reply  Tue Dec 3 18:15:42 2019, gautam, Update, ALS, EY uPDH post mixer LPF 
             Reply  Tue Dec 3 21:28:24 2019, gautam, Update, ALS, EY uPDH post mixer LPF uPDH.pdf
       Reply  Tue Dec 3 00:10:15 2019, Koji, Update, ALS, EY uPDH post mixer LPF 
          Reply  Tue Dec 3 00:51:25 2019, gautam, Update, ALS, EY uPDH post mixer LPF 
Message ID: 15066     Entry time: Tue Dec 3 18:15:42 2019     In reply to: 15060     Reply to this: 15068
Author: gautam 
Type: Update 
Category: ALS 
Subject: EY uPDH post mixer LPF 

Rana and I discussed this alogrythym a bit today - here are some bullet points, I'll work on preparing a notebook. We are still talking about a post-mixer low pass filter.

  • We want to filter out the 2f component - attenuation relative to the 1f content and be well below the slew-rate of the first post-mixer opamp (OP27).
  • We don't want to lose much phase due to the corner of the LPF, so that we can have a somewhat high UGF - let's shoot for 30kHz.
  • What should the order of the filter be such that we achieve these goals?
  • We will use a numerical optimization routine, that makes a filter that has
    • yy dB attenuation at high frequencies
    • sufficient stability margin
    • sufficiently small phase lag at 30 kHz so that we can realize ~30kHz UGF with the existing servo electronics.
Quote:

                   filter Q seems too high,

but what precisely is the proper way to design the IF filter?

   seems like we should be able to do it using math instead of feelins

                              Izumi made this one so maybe he has an algorythym
ELOG V3.1.3-