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LMH6629SDEVAL: Trying to use and test the component.

Dillon Buffone
Prodigy 20 points
Part Number: LMH6629SDEVAL

So I have the LMH6629SDEVAL board, and I am just trying to turn the amplifier on to get some performance specs.
I did not physically alter any components on the board, so all of the resistor values and such are still to spec.
I did not alter the positioning of the switches, because the AppNotes ("User Guide") wasn't exactly clear on the modes determined by the positions of the two switches.
Switch A: open, Switch B: closed. "Normal Operation"

I am using an Agilent E5062A Vector Network Analyzer (VNA), I know how to perform a two-port calibration for the VNA.
I connected "IN +" to Port 1 of my VNA, and "OUT" to a 20 dB Attenuator. I left PD floating, which defaults to logic 1, turning the amplifier ON. I left COMP floating, which does not matter, (I think), because I am not looking for a gain above 10 V/V, based on the circuitry given.
I left "IN -" floating, because I was not sure what to do with that, which I am sure is part of my issue.
I am unsure if I should connect a dummy load (50-Ohm Load) to the inverting input of the Eval board, or leave it floating.

After all of my calibration, I hooked everything up, making sure I did not lose my calibration (oh, yeah, I calibrated for my VNA's full frequency range: 300kHz to 3GHz), turned on my power supplies, 
and got a -50 dBm for S11, and something that was all around wrong-looking for S21.
(My goal is to figure out the amplifier's response as-is from at least 300kHz to around 750MHz (I am okay with poor response, I just want to see some data), and then do all of the stuff I need to, and re-test; I just want to make sure this board works, first)

I was wondering if anyone could tell an obvious mistake I had made, off the bat.
Thanks for reading this,
  -  Dillon

  • 0
    TI__Genius 15975 points
    Hi Dillon,

    What supplies are you using at the LMH6629SDEVAL board? I would start with +V = +2.5V, -V = -2.5V and GND pin tied to GND on the board. This would center the input common mode voltage to GND, and you should get an S21 as long as there is no alteration to the board. There is no termination required at the -IN because the RGB should not be populated on the board.

    I think you may have powered on the board with single +5V supply. There is nothing wrong powering the board that way but you would need to adjust the input common mode at the +IN to +2.5V as well, which will be within its input common mode operating range.

    Best Regards,
    Rohit