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ADCJ4000EVM bad at low frequenices

Other Parts Discussed in Thread: ADC12J4000EVM, ADC12J4000, LMH5401, LMH3401, LMH6401

Hi, Just wondering if you have any ideas to improve the ADCJ4000EVM at low frequencies, would the balun on the board be causing this at all?

  • Hi Michael

    As noted in the Introduction section of the ADC12J4000EVM User Guide, the balun transformer coupled input is rated for 400 MHz to 3 GHz.The ADC12J4000 device itself has excellent performance all the way down to DC input signals.

    If you want to operate the EVM with lower frequency input signals you can reconfigure the board for differential AC-coupled or DC-coupled input. In that configuration you will need to apply a differential signal, so may need to use an external balun or amplifier EVM to perform single-ended to differential conversion.

    The changes needed to enable differential input signals have been addressed in this previous E2E post here:

    Best regards,

    Jim B

  • Thanks Jim,
    I just have a question about baluns and differential signals. The system will be used for PDOA. Am I correct in thinking that a phased matched balun would be needed, as a phase delay in one of the differential lines would then in effect stretch the waveform out. As it is basically impossible to phase match something to 1 deg at 5GHz, is there a way of calibrating out the phase delay in one of the differential inputs on the adj12j4000. I'm thinking something like characterizing the input signal shape and then comparing the deviation on the sampled signal.
  • Hi Michael

    There are a variety of baluns available at different quality and price points.  If the frequency range is not too big it is possible to get baluns with relatively low (1 degree typical) phase mismatch on the differential outputs. If the frequency range of your signals is relatively low, the relative phase mismatch between Fmin and Fmax will also be relatively low.

    Depending on your signal frequencies you could consider a differential amplifier instead of a balun. The LMH3401, LMH5401 and LMH6401 would be good devices to consider.

    I hope this is helpful.


    Jim B