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Observer tasker.j
Observer
133 Views
Registered: ‎10-23-2018

RFSoC RF DAC data stream format & Example

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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4 Replies
Moderator
Moderator
93 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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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Observer tasker.j
Observer
87 Views
Registered: ‎10-23-2018

Re: RFSoC RF DAC data stream format & Example

Hi Keith,

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

-Jim

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Moderator
Moderator
50 Views
Registered: ‎04-18-2011

Re: RFSoC RF DAC data stream format & Example

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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Observer tasker.j
Observer
36 Views
Registered: ‎10-23-2018

Re: RFSoC RF DAC data stream format & Example

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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