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DAC3161 single ended output

Mike Wang2
Intellectual 2760 points
Other Parts Discussed in Thread: ADS62P28, DAC3161

Hi,

My customer want to use DAC3161, but it's not in a traditional wireless communication application. they use the DAC and high speed amp to drive a cable and then use ADS62P28 to sample the signal at the other end of the cable. Now they want to do the single ended output like below:

But in the datasheet, we don't have a typical app like that, is the DAC3161 able to support this kind of termination? what would be the primary concern for this?

In datasheet, it is said "The data format is interleaved with channel A (rising edge) and channel B falling edge". but I don't see the 3161 could be configured as this since it only have one channel. Is this a typo?

Thanks.

BR,

Mike

  • 0
    TI__Mastermind 29220 points

    Hi,

    Fundamentally there should be no reason why the circuit you describe would not work, since both sides of the differential output see a 25 ohm load each.  So this should work.  But any imbalance due to tolerances of components or trace impedance between the two sides would degrade performance.   The EVM for the device also outputs a single ended signal on an SMA connector, but uses transformer coupling to do so.  That would be preferable, unless the low end of the passband of the transformer limits the bandwidth of your signal since the transformer essentially blocks DC and very low frequencies.

    This family of devices include 1 and 2 channel versions, so yes it would be a typo that the datasheet for this device still mentions the second channel in the section on the sample data interface.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    TI__Intellectual 2760 points
    Hi Richard,

    Thanks for you reply. Could you please explain why the transformer helps eliminate the imbalance caused by tolerances of components or trace impedance?

    BR,
    Mike
  • 0 in reply to Richard Prentice
    TI__Intellectual 2760 points
    Hi Richard,

    If I use DAC3161 as the single ended output topology above, and IoutA/B is terminated with 50 ohm resistor. when the output current reaches 20mA, the voltage on Iout- would be -1V. it is out of the compliance voltage range (-0.5V to 1V). Does it mean the current limitation is 10mA in this case?

    BR,
    Mike
  • 0 in reply to Mike Wang2
    TI__Mastermind 29220 points

    Hi,

    If you use a transformer to couple the output to single ended, then you would be able to keep the signal truly differential and balanced up to the transformer primary coil, and then if the transformer is 1:1 ratio then whatever load the transformer sees would mean that the DAC sees load/2 on each leg of the output.

    in the original sketch you showed an effective load of 25 ohms on each side of the differential which would be within compliance voltage range.  I don't think you could change that to 50 ohms each.  If you did use transformer coupling then you could also change the turns ratio to 1:2 or 1:4 for more flexibility in your design.

    Regards,

    Richard P.