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Contributor
Contributor
1,381 Views
Registered: ‎10-23-2018

RFSoC RF DAC data stream format & Example

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Hi,

I'm referencing the rfdc-data-write-example for the ZCU111 (part of the TRD) and am confused about the constant data that is fed to the DAC.  If I plot the raw 1024 byte array, I get the following plots (full & zoom):

1300Mhz_Data.jpg1300Mhz_Data_zoom.jpg

I was expecting the data to look like an AC coupled sine wave tone with constant amplitude.  Why does it not look like this? Is the I & Q data interleaved in this array?  If so, I would expect that if I took every other sample and plotted it I would get me back to the expected waveform, but I do not get that either.  I've read the PG269 regarding the digital data format, and the data in the sine_wave array provided looks correct.  I've verified on a spectrum analyzer that I do indeed get 1300 MHz.

Also, how is the frequency of the sine wave calculated?  I'm not sure how to go from the 6.554 Gsps for the DAC to the 1300 MHz sine wave.  It looks like there are multiple periods of the waveform in the constant array; but, could the array be significantly shortened to a single period of data points? How could I then calculate the resultant waveform?  My long term goal is to write a function that will generate an array of bytes for a waveform based on user inputs and send them to the DAC, but I have to understand the data format first.

Any help or insights would be greatly appreciated.  Thanks in advance and please let me know if I can clarify anything.

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Moderator
Moderator
1,230 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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We think that this is just the effects of sampling. I think the period of the 1300Mhz sine is just an odd sub multiple of sampling period. If you look at the fundamental the amplitude is not changing.

 

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9 Replies
Moderator
Moderator
1,341 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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Hi @tasker.j

 

I need to take a look here. I have never used this application. 

I wonder if this is just formatted in such a way that it makes the output nice once interpolation is done. 

Let me see about trying it here. 

Keith 

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Contributor
Contributor
1,335 Views
Registered: ‎10-23-2018

Re: RFSoC RF DAC data stream format & Example

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Hi Keith,

Thank you very much for taking a look as I am still working on this.

-Jim

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Moderator
Moderator
1,298 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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Hi @tasker.j

Can you perhaps share the FFT of the DAC output. Are you seeing a big harmonic at the same frequency as the envelope around this signal?

Keith 

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Contributor
Contributor
1,284 Views
Registered: ‎10-23-2018

Re: RFSoC RF DAC data stream format & Example

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Hi @klumsde,

Below are some screen shots of the actual and theoretical FFT's of the 1300 MHz data in the rfdc-data-write-example.  I do not see a big harmonic at the same frequency around the signal.

IMG_2256.resized.JPGIMG_2258.resized.JPG

Theoretical Model with the provided data:

theoFFT.jpgtheoFFT2.jpg

Thanks again and please let me know if you need any other information.

-Jim

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Moderator
Moderator
1,246 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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Hi @tasker.j

Still looking into this here. 

Its seem like this behaviour is mirrored in the GUI. 

Requesting a 200Mhz tone and everything is fine, you get a fixed amplitude sine wave. 

As you proceed up towards 1300MHz as you have the problem gets more and more pronounced dac200.JPG

 

dac1300.JPG

 The developer of the GUI has been made aware of it. 

I will keep you posted on what we find. 

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Moderator
Moderator
1,231 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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We think that this is just the effects of sampling. I think the period of the 1300Mhz sine is just an odd sub multiple of sampling period. If you look at the fundamental the amplitude is not changing.

 

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Contributor
Contributor
696 Views
Registered: ‎11-21-2018

Re: RFSoC RF DAC data stream format & Example

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Hi,

where is it possible to find that files? 

#include "rfdc_interface.h"
#include "data_interface.h"
#include "clock_interface.h"
#include "rfdc_functions.h"

I would like to use the rfdc-data-write-example.c in SDK and start with this test.

Thank you for your time,

Regards.

 

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Contributor
Contributor
690 Views
Registered: ‎10-23-2018

Re: RFSoC RF DAC data stream format & Example

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These files are located in the zcu111 technical reference design archive (rdf0476-zcu111-rf-dc-eval-tool-2018-3.zip) under apu/rfsoc_petalinux_bsp/project-spec/meta-user/recipes-apps/rfdc-data-write-example.  I've attached an archive of these files for convenience.  

Hope this helps.

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Contributor
Contributor
679 Views
Registered: ‎11-21-2018

Re: RFSoC RF DAC data stream format & Example

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Many thanks for your help,

Yes, I think it will be easier to understand how to write datas in DRAM memory.

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