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Adventurer
Adventurer
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Registered: ‎02-08-2016

RFSOC DAC single ended output

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Hi,
 
I wonder if you can help me. I am using the RFSOC DACs in single-ended mode with max_current = 30mA and DAC_AVTT in default voltage.
The output of the DAC's never swings far below 0V.  I generated a sawtooth waveform and verified it is correct using ILA. The DAC output swings between approx 1.5V and -0.1V
 
If DAC_AVTT = 2.5V should I expect a digital input to the DACs of 0x0000 to correspond to an output of 0V or 2.5V ?
 
what is the reccomended voltage configuration of non-differential output mode?
 
How do I change the DAC_AVTT voltage ?
 
Many thanks
 

Simon Hildebrand

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Teacher
Teacher
681 Views
Registered: ‎07-09-2009
The DACs don't have a negative supply, so can not output a negative voltage.
They are also current out put devices,
its the direction of the current that determines if the signal is viewed negative or positive.

To use the DAC's singe ended, you need to either put a transformer or a differential buffer amp on them. If you want negative voltage your amp will need a negative supply.

This could be of use
https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>

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Moderator
Moderator
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Registered: ‎04-18-2011

The DAC takes in a 16-bit 2's compliment sample and converts it at the differential output. 

I don't think we can support this configuration. 

What is the usecase for doing this? 

Normally if you have a RF instrument that is single ended we use a balun to connect the DAC to the spectrum analyzer for example. 

 

Keith

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Highlighted
Teacher
Teacher
682 Views
Registered: ‎07-09-2009
The DACs don't have a negative supply, so can not output a negative voltage.
They are also current out put devices,
its the direction of the current that determines if the signal is viewed negative or positive.

To use the DAC's singe ended, you need to either put a transformer or a differential buffer amp on them. If you want negative voltage your amp will need a negative supply.

This could be of use
https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>

View solution in original post

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Adventurer
Adventurer
659 Views
Registered: ‎02-08-2016

Hi,

It now makes sense. I am using the ZCU111 and XM500 daughter board. I have now loaded the schematics for the XM500 daughter board.

It seems that DACs 04,05 are connected via transformer etc to convert them to single ended 1-4GHz output, DACs 06,07 are connected via transformer as LF outputs 0-1GHz. The DACs 00-03 are directly available as differential outputs.

Please see attached image.

 

Simon

 

DAC.png