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LMH6553: Cascade configuration

na na78
Guru 16770 points
Part Number: LMH6553


Hi

Could you please review the following configuration for LMH6553?

①　We assume cascaded connection of LMH6553(G=8) like the figure.  Do you see any mistakes?

②　A positive output of 2nd LMH6553 would not be used for comparator stage.  Is the RC circuit in dotted circle not needed?

③　Is the termination for the 1st and 2nd LMH6553 required additionally?  What kind of termination would be needed?

BestRegards

  • 0
    TI__Genius 15975 points
    Hi,

    To answer your questions:
    1. I think the LMH6553 could be used in the cascaded connection as you have shown and I don't see any probable mistake. However, your output will be clipped most of the time due to the clamping action of the LMH6553 and high gain (~68.62x) in the circuit. The intention here is to generate a square wave from a sinusoidal signal that is cleaned by the comparator, right?
    2. I would recommend to keep the RC circuit of the 2nd LMH6553 positive output just because it acts as dummy terminated impedance to the negative output that drives the comparator.
    3. Are you talking about the termination at the input, or the output? About the 2nd stage LMH6553 output, I would recommend on making the comparator input impedance that is connected to the 2nd LMH6553 output as 100-ohms, similar to what it will drive on the positive output. The 1st stage LMH6553 drives a 94-ohm output load realized by the 2nd stage Rg resistors (47-ohms) and should be ok.

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    Guru 16770 points

    Hi Rohit

    Thank you for your reply.

    Regarding to the answer 3, I want to make sure the following.

    >I would recommend on making the comparator input impedance that is connected to the 2nd LMH6553 output as 100-ohms,

    >similar to what it will drive on the positive output.

    I assume the following image.  Is it correct?

    (In addition, AC coupling at 2nd stage LMH6553 output was eliminated due to the comparator with single supply.)

    If it is not what you intended, could you please point it out?

    BestRegards

  • 0 in reply to na na78
    TI__Genius 15975 points

    Hi,

    I would recommend to include a placeholder of 20-ohm series resistor at the second stage LMH6553 output while driving the comparator input.

    Best Regards,

    Rohit