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LMH6518: Single-ended DC-coupled output

Mark Krangle
Prodigy 50 points
Part Number: LMH6518
Other Parts Discussed in Thread: THS3217, THS3491

Hello,

I'm interested in using the LMH6518 in an application that requires a 50 ohm single-ended, DC-coupled output with about 500 MHz bandwidth.  I'm looking for recommendations on how to implement this for this amplifier, or any other FDA for that matter.

Since the output must be DC-coupled, I can't use a balun.  Is the right approach to follow the LMH6518 with another high-speed op amp configured as a differential amplifier? If so, any suggestions on an op amp part number?  Or, even better, is there a fully integrated component that I could use that would have better CMRR?

Thanks for your help.

-Mark

  • 0
    TI__Genius 15975 points
    Hi Mark,

    Could you let us know the maximum swing needed for your 50-ohm single-ended, DC coupled output with 500MHz BW?

    Yes, an FDA followed by a difference op-amp would be the best approach for differential to single ended conversion, if you don't intend to use a balun. I don't think we have a fully integrated component yet for variable gain FDA along with the differential to single ended conversion. For a differential amplifier recommendation, you might want to take a look at the THS3217 which can do diff-to-single ended conversion from DC to 800MHz BW. Also, the THS3491 CFB op-amp could be used in diff to single ended configuration and can achieve the required DC to 500MHz BW.

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    Prodigy 50 points

    Hi Rohit,

    Thank you for your reply.  The output voltage swing is +/- 500 mV.

    I have been looking at the THS3217 and that seems to be a good option.  In fact, figure 68 of the datasheet shows the exact configuration I need, except with a different FDA.  I think I will order some eval boards so I can try it out.

    Thanks again for your help.

    Regards,

    Mark