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Interfacing LMH6629 with kHz Coil Antenna

Albert Lu1
Intellectual 520 points
Other Parts Discussed in Thread: LMH6629, TINA-TI

Hey All, 

I'm planning to use the LMH6629 with an multi-turn coil antenna around 30~300 kHz, but I am undecided between using it in the inverting or the non-inverting configuration, and how to achieve the best SNR.  Below are my thoughts, please feel free to correct me if I'm wrong.

1.  In the Inverting mode,  the input impedance of the op amp will be the input resistor Rg, where Av = -Rf/Rg. Rg is easily matched to the real part of the coil antenna. Although power matched, it may not be noise matched.

2.  In the non-inverting mode, I think the antenna can generate a lot more voltage at the non-inverting input, or just have it unterminated, to minimize the NF.

3.  Incorporate a 1:4 turn transformer such as the http://www.minicircuits.com/pdfs/T36-1.pdf to further boost the NF.

Let me know your thoughts

Thanks,

Albert

  • 0
    TI__Mastermind 22825 points

    Hi Albert,

    I've tried the LMH6629 with a front-end transformer to minimize Noise Figure (NF) and I was able to reduce NF by 2.3dB. I had not used the optimum turns ratio which is 3.3 for LMH6629:

    In my setup, the transformer turns ratio was 2.83. Below is a report on this topic.

    5618.NF Improve 9_25_14.pptx

    I think you'll have a better chance with the non-inverting configuration because you have more freedom to select / adjust your input impedance. You can use TINA-TI and LMH6629's model to predict output noise accurately as the noise model is very accurate (voltage and current noise, flatband and 1/f region both).

    Regards,
    Hooman