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LMH6521: Using dual LMH6521 in signal path

David Wende
Intellectual 620 points
Part Number: LMH6521
Other Parts Discussed in Thread: LMH6629, LMH6517, LMH6518

Hello,

I would like some feedback in order to choose the best signal path for the following:

Input signal is single-ended 5-100MHz, with amplitude ranging over 300uVpp and 300mVpp.

I want to drive a differential ADC 2Vpp.

Noise performance is most critical issue here.

I had thought of using the LMH6629 in a gain of around 20 followed by both halves of the dual LMH6521 in series.

Using dual VGA will give me a variable gain over the 60dB that I need, and using a low noise gain block prior to VGA should render the noise of the VGA less significant.

 

In addition, are there any recommendations for driving LMH6521 by single-ended signal?

Thank you.

  • 0
    Guru 140200 points

    Hi David,

    the datasheet of ADC usually recommends a suited driver for the inputs.

    Kai

  • 0
    Intellectual 620 points

    Hi Kai,

    Thanks for your reply, however I am interested in the interface between LMH6629 (single ended output) and LMH6521 (differential input).

  • +1 in reply to David Wende
    TI__Mastermind 24145 points

    Hello David,

       For second stage, LMH6521 would work, but also look into LMH6517 and LMH6518. Looks like for first stage, you chose our very low noise amplifier, this amplifier is decompensated which is ideal for high-gain designs such as this application. It is better to have a higher gain in the first stage compared to second stage of a multi-stage amplifier solution for better overall noise performance. So set the first stage as high gain as possible while also meeting your 100MHz system bandwidth, and the rest of the gain can be varied through the second stage. Here is also a link of a good example of single ended to differential amplifier setup.

    Thank you,

    Sima