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
Entry  Thu Jan 27 17:12:02 2011, Aidan, Joe, Summary, Green Locking, Digital Frequency to Amplitude converter Screenshot.pngSwept_sine_F_to_A.png
    Reply  Thu Jan 27 23:21:50 2011, rana, Summary, Green Locking, Digital Frequency Discriminator 
       Reply  Fri Jan 28 09:03:38 2011, Aidan, Summary, Green Locking, Digital Frequency Discriminator 
          Reply  Tue Feb 8 10:23:02 2011, Aidan, Summary, Green Locking, Digital Frequency Discriminator - reference 
    Reply  Fri Jan 28 10:27:46 2011, Aidan, Joe, Summary, Green Locking, Digital Frequency Discriminator - calibration 
Message ID: 4217     Entry time: Fri Jan 28 09:03:38 2011     In reply to: 4216     Reply to this: 4259
Author: Aidan 
Type: Summary 
Category: Green Locking 
Subject: Digital Frequency Discriminator 

Quote:

That's some pretty fast work! I thought we would be taking up to a week to get that happening. I wonder what's the right way to measure the inherent frequency noise of this thing?

Also, should the comparator part have some hysteresis (ala Schmidt trigger) or is it best to just let it twirl as is? Is it sensitive to DC offsets on the input or is there a high pass filter? What's the correct low pass filter to use here so that we can have a low phase lag feedback to the ETM?

 

We could try inputing a 4kHz carrier modulated width a depth of a few Hz at a modulation frequency of F1. Then we could take an FFT of the output of the discriminator and measure the width of the peak at F1 Hz. This seems like an arduous way to measure the frequency noise at a single frequency though.

It'll definitely be sensitive to DC offsets but there is already a filter bank on the INPUT filter so we can shape that as necessary. We could probably band-pass that from [4.5 - 5.3kHz] (which would correspond to a range of [73,87] MHz into a 2^14 frequency divider.

 

ELOG V3.1.3-