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LMH6882EVAL: Baluns and Evaluation Board Frequency Range

Benjamin Domae
Prodigy 10 points
Part Number: LMH6882EVAL

Over what frequency range does this evaluation board operate? I know the amplifier chip itself can operate between 0-2.4 GHz, but the baluns listed on the schematic/in the pictures (Mini-Circuits JTX-2-10T+) seems to only operate over 0.05-1 GHz and is matched for 75 ohms (and 150 ohms differential) instead of 50 ohms (and 100 ohms differential). Is this the correct balun? If it is, does that mean that the eval board (when used in its default single ended configuration using the baluns) only works under 1 GHz?

  • +1
    Guru 48195 points

    Well Benjamin, you are correct the balun will limit the BW. For folks with single ended 50ohm equipment you have to do this. The full broadband curves where probably taken with a 4port network analyzer and no baluns, 

    Also, here is my model of the JTX-2-10T, little better with 75ohm that spec, might match my measurements some years back, 

    If you go down in impedance, that will shift the passband down, actually quite a lot, this 2nd test in file below, Incidentally, this simple Balun model does not capture the relatively large 1.4dB insertion loss for this balun - those numbers come from a single typical device bench measurement. 

    JTX-2-10T Balun Simulation.TSC

  • 0 in reply to Michael Steffes
    Prodigy 10 points

    Thanks Michael, that's really helpful! I'm glad to know I'm not crazy, but that is a bit discouraging for my intended application. I intended to use these for a FPGA/ADC interface with differential inputs, so I could avoid getting the VGAs and separate baluns to have single-ended inputs to the overall system.  Looks like I'll need to modify these boards to use the differential inputs/outputs and also get separate baluns.