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LMH5401: Active Termination

Apurva Gowda
Prodigy 220 points
Part Number: LMH5401

Hi,

Is it possible to actively terminate the LMH5401 to get 5.2-5.5Vpp differential out such that the output resistor appears to be 50ohms when viewed from the line? Are there any performance degradations, such as higher noise figures or non-linearity impairments that result from active termination?

Thanks,

Apurva Gowda

  • 0
    TI__Genius 15975 points
    Hi Apurva,

    I think you should be able to actively terminate the LMH5401 output, but I am a little doubtful of the 5.2-5.5Vpp differential output with good linearity performance at high frequencies. The LMH5401 max differential output is limited to 5.8Vpp differential, so 5.5Vpp differential would be pushing the part. The LMH5401 S-parameters I provided have the 50-ohm on board resistor on each output. So, I would recommend you to account for those resistors while building the active termination circuit.

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    Prodigy 220 points
    Thanks Rohit. Yes, we are trying to push the amplifier to max voltages. However, we are only looking at pulses with pulse widths in the 500ps to 1ns range (bandwidths of 1-2GHz). By high frequency, do you mean 1-2GHz or greater than that?

    Also, is it possible for noise figure to increase due to active termination?

    Regards,
    Apurva Gowda
  • 0 in reply to Apurva Gowda
    TI__Genius 15975 points
    Hi Apurva,

    I think it would be tough to maintain the maximum voltage of 5.2-5.5Vpp differential in the 1-2GHz range using the LMH5401, as you would start getting into compression issues at these frequencies. I would recommend you to evaluate the LMH5401 part on a bench using the LMH5401EVM: www.ti.com/.../LMH5401EVM, in-order to make sure whether it fits your application requirement.

    I don't think the noise figure should increase due to active termination because you are implementing the active termination at the LMH5401 output.

    Best Regards,
    Rohit