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Entry  Fri May 17 18:58:58 2013, Jamie, Koji, Summary, CDS, Weird DAC bit flipping at half integer output values const.pdfsweep.pdf
    Reply  Fri May 17 19:56:52 2013, Koji, Summary, CDS, Weird DAC bit flipping at half integer output values 
    Reply  Wed May 22 11:09:33 2013, Jamie, Summary, CDS, Weird DAC bit flipping at half integer output values nopad.pdf
       Reply  Wed May 22 11:21:28 2013, Koji, Summary, CDS, Weird DAC bit flipping at half integer output values 
          Reply  Wed May 22 11:35:06 2013, Jamie, Summary, CDS, Weird DAC bit flipping at half integer output values 
             Reply  Wed May 22 15:08:37 2013, Koji, Summary, CDS, Weird DAC bit flipping at half integer output values Screenshot.png
Message ID: 8613     Entry time: Wed May 22 11:09:33 2013     In reply to: 8598     Reply to this: 8614
Author: Jamie 
Type: Summary 
Category: CDS 
Subject: Weird DAC bit flipping at half integer output values 

After querying CDS folks about this issue, I got some responses that indicated the problems was likely limit-cycle oscillations due to zero-padding of the data when upsampling.  Tobin ran some Matlab tests to confirm this issue.

Starting in RCG 2.5 there is a new "no_zero_pad=1" cdsParameters option turns zero padding OFF.  I tried enabling this option c1scy to see how the behavior changed.  Sure enough, the 32 kHz oscillations mostly went away.  There are no oscillations for outputs held at the half-count value, and the oscillations around the half-count transitions went away as well.

The only thing I could see is a bit of oscillation when converging on a constant half-count value that went away after a couple of milliseconds:

nopad.pdf

So we might consider adding the no_zero_pad=1 option to all of our coil driver outputs, which might eliminate the need to add notches at the Nyquist in the analog anti-image filters

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