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Visitor rwestafer
Visitor
1,273 Views
Registered: ‎02-14-2019

RFSoC MTS ADC capture glitches

REVISED:

We are finding glitches in captures from the MTS demo using the demonstration GUI.  See attached images showing spikes and skips.

* Seemingly random spikes occur differently across all channels (3 shown).

* Somewhat periodic phase jumps occurs the same way across all channels.

I also should say that we once observed captures without any such glitches.  Pleasantly surprised, we saved the preferences and configuration to file, power cycled the ZCU111 board, closed the GUI, reopened it, loaded the stored config and preferences, but the glitches were back.

1. Any ideas what causes these different artifacts?

2. Anyone else experience this (or not experience it)?

3. How can we reliably get a good/clean starting point with the MTS load for the ZCU111?

spikes_different_across_channels_MTS.png
phase_jumps_all_channels_MTS.png
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19 Replies
Teacher drjohnsmith
Teacher
1,228 Views
Registered: ‎07-09-2009

Re: RFSoC MTS ADC capture glitches

do you mean spurs ?

 

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Visitor rwestafer
Visitor
1,222 Views
Registered: ‎02-14-2019

Re: RFSoC MTS ADC capture glitches

Two different artifacts are shown in the time domain.  Their spectral responses are different.

  • The "spike" artifact is broadband, and so it raises the noise floor uniformly in the frequency spectrum; not a "spur"
  • The "phase jump" artifacts occur somewhat periodically, and so they do result in spur-like spectral features, but I also would not call these "spurs" (in the usual intended meaning that refers to harmonics or intermodulation products).
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Teacher drjohnsmith
Teacher
1,212 Views
Registered: ‎07-09-2009

Re: RFSoC MTS ADC capture glitches

Sorry, I can't see any pictures, so it was a general question.
I should have said.
Hows it look compared to the data ?
Are you getting the SFDR your expecting ?
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Visitor rwestafer
Visitor
1,194 Views
Registered: ‎02-14-2019

Re: RFSoC MTS ADC capture glitches

Updated the original post; clarified and attached photos instead of pasting inline with text.

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Teacher drjohnsmith
Teacher
1,164 Views
Registered: ‎07-09-2009

Re: RFSoC MTS ADC capture glitches

WOW,

That I agree with you is not right.
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Teacher drjohnsmith
Teacher
1,150 Views
Registered: ‎07-09-2009

Re: RFSoC MTS ADC capture glitches

Ive just seen this,

https://forums.xilinx.com/t5/Evaluation-Boards/ZCU111-RF-Data-Converter-Eval-design-generates-VDMA-errors-on/m-p/935837/thread-id/20587

 

is it relevant ?

 

Your glitch looks way to drastic to be in the adc, more likely in the data capture side.

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Moderator
Moderator
1,144 Views
Registered: ‎04-18-2011

Re: RFSoC MTS ADC capture glitches

Hi @rwestafer

@drjohnsmith is right to point out this issue. In this case the problem with the DMA is still being debugged. 

What size is your capture buffer in this example?

As an exercise can you reduce the size of the bufffer to 2097152 samples or below? Does the issue go away then?

 

Keith 

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Visitor rwestafer
Visitor
1,143 Views
Registered: ‎02-14-2019

Re: RFSoC MTS ADC capture glitches

Thanks for finding that issue with large sample sizes.  The affected captures in the case of this topic are only 8192 samples; this topic appears to be unrelated to that particular VDMA error issue.

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Moderator
Moderator
1,128 Views
Registered: ‎04-18-2011

Re: RFSoC MTS ADC capture glitches

OK so what is the metal log telling you?

 

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1,078 Views
Registered: ‎02-04-2019

Re: RFSoC MTS ADC capture glitches

Hello,

We are having the same issues with spikes and skips as shown by the photos below. If anyone has any suggestions or ideas on why this is occuring it would be greatly appreciated.

 

Capture.PNGZoomed Out Version with SpikesCapture2.PNGSudden Phase ChangeCapture3.PNGSudden Phase Change

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Teacher drjohnsmith
Teacher
1,071 Views
Registered: ‎07-09-2009

Re: RFSoC MTS ADC capture glitches

That looks like the phase inverts, like a bi phase encoded signal..
Just an analog suggestion, turn down the signal power, may be 6 dB. I'm 99 % certain it will not affect more than the amplitude, but I have seen it happen once that another companies chip did similar funnies with to much power into its input amp.
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Visitor rwestafer
Visitor
1,046 Views
Registered: ‎02-14-2019

Re: RFSoC MTS ADC capture glitches

I don't recall any metal log errors; nothing seems to correlate with the occurrence of these artifacts.

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Visitor gtri-samo
Visitor
1,015 Views
Registered: ‎03-11-2019

Re: RFSoC MTS ADC capture glitches

Follow up to sehejahluwalia 's post:

We believe to have determined that the spikes have a high probability of occurring with periodicity of approximately 256 samples. Therefore, it is our assumption that the glitches are due to the memory buffers being written and read simultaneously. The way we had tested this was to set the frequency of the signal relatively low, 20 MHz, and samples to some low number; 1000 was used for our experiment. Phase skipping was uniformly observed under these conditions. Furthermore, upon decimation the signal had lower likelihood of glitching.

Question then becomes; is the FPGA reading from a register in memory being written to... If so, how can we resolve this issue?

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Visitor pojotis
Visitor
672 Views
Registered: ‎12-18-2018

Re: RFSoC MTS ADC capture glitches

Hello

we are having the same problem in our board. And due to these random phase jumps etc. there are a lot of spurs in the sampled signal.

Is there any solution that you could find? Can you please share them with us?

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Visitor rwestafer
Visitor
662 Views
Registered: ‎02-14-2019

Re: RFSoC MTS ADC capture glitches

On review of the reference design, it looked like the buffers were overrun periodically, depending on the sample rate... there are various solutions, including simply reducing the sample rate.  Also, but likely unrelated, we found that the rf_tool program on the PS will segfault or crash occasionally, and launching the program again did not resolve the issue (power cycle to the board or restart of the PS was required).  There are numerous issues with the reference design, but it serves its purpose.

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Visitor pojotis
Visitor
656 Views
Registered: ‎12-18-2018

Re: RFSoC MTS ADC capture glitches

Thnx for your answer.by saying reducing sampling frequency, what is the reduced sampling frequency on your trials? Even we reduce from 4Gsps to 1Gsps we observe the same problems in our board. Can you please advise a sampling frequency with which you observe no problems.

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Explorer
Explorer
441 Views
Registered: ‎06-19-2014

Re: RFSoC MTS ADC capture glitches

was this issue resolved? I am having same problem.

Capture1.PNG
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Visitor pojotis
Visitor
433 Views
Registered: ‎12-18-2018

Re: RFSoC MTS ADC capture glitches

In MTS mode we figured out that internal PLLs should always be bypassed. Otherwise no matter what you do, you cannot get rid of glitches etc. Hope that your problem is related to that.

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Explorer
Explorer
416 Views
Registered: ‎06-19-2014

Re: RFSoC MTS ADC capture glitches

I am giving clock from external PLLs not internal still have this issue.

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