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LMH5401: Multiple LMH5401 In series to get more gain.

Leo A.
Intellectual 515 points
Part Number: LMH5401

Hello,

I have 100ohm differential output that I need to amplify. The output ranges from 5.7mVpp to 1.4Vpp. The frequency will be between 32Mhz and 1GHz.

This output needs to be amplified to provide a minimum of 150mVpp swing into the device that we need to drive.

I have a design using three LMH5401 amps. It works really well bringing up the 5.7mVpp waveform to 150mVpp.

The same circuit does not behave too well with 1.4Vpp input the amplifier outputs are clipped to the rail which would be ok but it would seem like there are some other effects going on at least in the simulation.

Please take a look and let me know what would be the best way to proceed.

P.S. I need to use the LHM5401 because it is also available in the SP variant.

APD_RF_CHAIN.TSC

  • 0
    Guru 47485 points

    Well yes Leo, driving the outputs into the rails gets into overdrive recovery specification - not well known for a part like this, 

    What you are describing sounds kind of like a comparator or gain compression ckt. 

    I think there might be some RF diff I/O amps that have good gain compression without too much phase dispersion with overdrive level - not sure about the SP aspect there -

    There are gain compression tricks with a part like the LMH5401, but that gets more part intensive, again not so suitable for and SP need.