Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 48 subscribers
  • Views 2194 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS3217: High Linearity DAC driver

xyz xyz
Intellectual 1000 points
Part Number: THS3217
Other Parts Discussed in Thread: DAC5672,

Hello

I have a 275MSPS high speed DAC (DAC5672).

usually the DAC driver is a difference amplifier with two Rt resistors at the output current of the DAC as shown below:

I want to maximize the CMRR and Linearity.

if I want to maximize the CMRR, I should minimize the miss-match between the resistors in the difference amplifier. I have found some resistor networks like below:

but the size is as shown below:

another option is THS3217, there are two unity gain buffers at the input:

now the advantage is use of two 49.9 Ohm resistors as Rt, (I don't need the Power Amp)

my signal should be 2Vpp and the HD2 should be better than 90dB.

now which option do you recommend me?

Best Regards

  • 0
    TI__Expert 8380 points
    Hi,

    What is you maximum system frequency that you plan to produce from the DAC? The THS3217 is a very easy interfacing solution but it cannot maintain 90dB for its entire frequency range.

    Regards,
  • 0 in reply to Jacob Freet
    Intellectual 1000 points

    Thanks for your attentions :)
    I should keep the SFDR around 90dB and SNR>70dB within 10MHz. bcoz I want to keep the maximum performance of the DAC.
    *actually THS3217 has all parts of the first solution in itself.
    *with the first solution I have concern about the size of resistor network.
    *what would have happened if THS3217 didn't have two unity gain buffers? ( I guess some reflections and mismatch issues)
    *I don't need the Power Amplifier, can I realize THS3217 with two ultra low distortion buffers and one difference amplifier? I think the difference amplifier with +2 of a gain causes distortion in THS3217.

  • 0 in reply to Jacob Freet
    Intellectual 1000 points

    Dear

    another question is:

    I have found a note in THS3217's datasheet.

    at page 24:

    you have used a function generator to produce a pure signal. but the purity  is 100dB :) I'm wondered how did you produce it? your function generator is special?

    Thanks

  • 0 in reply to xyz xyz
    TI__Expert 8380 points
    Hi,

    To achieve the 100dB performance we use a very high order bandpass filter following the function generator that eliminates the harmonic distortion generated by the signal source.

    Since you don't need the power amplifier, you can actually use the THS3217 with the power amplifier stage shut down. Then it just functions as two input buffers with the differential-to-single stage.

    Regards,
    Jacob
  • 0 in reply to Jacob Freet
    Intellectual 1000 points
    interesting
    How do you change the center frequency of your BPF?
    actually I'm looking for such filter.
    Thanks
  • 0 in reply to xyz xyz
    TI__Expert 8380 points
    Hi,

    We actually use separate filters for each measurement. We have a bank of TTE brand passive filters that we switch between using a high fidelity RF switch. If we need even more accuracy, then we connect to filters manually.

    Regards,