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The waveform from differential to single-ended output for DAC3161

user4304151
Prodigy 30 points
Other Parts Discussed in Thread: DAC3161

Hi Dear,

I followed the reference design DAC31X1EVM to get a single-ended output by transformer coupling, the schematic is below:

The waveform I want to get likes this:

The problem is the waveform is not expected behind those two transformers:

1) the waveform at DAC3161 side is below, there, green waveform is from a pin P, yellow waveform is from

    pin N when I removed the resistor R311,R312. The waveform is right if I make a substruction of Vp-Vn.

    

2) When I re-populated resisters R311, R312, the waveform likes below:

   

So, I can not get the waveform I expected by transformer coupling, is it right?

if Yes, could you give some suggestion to get the expected waveform.

Thanks a lot!

Gideon

  

  • 0
    TI__Guru* 91947 points

    Gideon,

    We are looking into this.

    Regards,

    Jim

  • 0 in reply to jim s
    TI__Mastermind 29220 points

    Hi,

    The center tap on the primary of the transformer is what is setting the common mode of the signal swing, and the center tap is grounded so the signal is swinging about ground.   When you remove R311,R312 you are cutting off that portion of the circuit that is biasing the signal swing.   You can use the center tap of the transformer to set the common mode of the signal to wherever you like it, as long as the signal remains within the compliance range specified for the DAC.  

    If you remove the 0 ohm resistor R313 then the common mode of the swing would return to where you see it without R311,R312.    Or you could apply a desired common mode voltage of your choosing to the center tap of the transformer.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 30 points

    Hi Richard,

    Thank you a lot for your prompt reply, I'll try it.

    Gideon