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LMH6518: Interfacing high-impedance adcs

Chris SP
Prodigy 10 points
Part Number: LMH6518


Hello everybody,

I would like to know if it's possible to drive with the LMH6518 ADCs which have an differential input impedance around 20k.

In the datasheet only 100 Ohm differential ADCs are recommended. Will the bandwidth of the implemented filter stay the same if the impedance of the ADC is too high?

Thank you very much for helping me!

 

  • 0
    TI__Genius 15975 points

    Hi Chris,

    It is possible to drive the LMH6518 into an ADC which has a differential input impedance of around 20k. However, one thing you need to be careful of is the increased input reflections from the ADC at higher frequencies due to source and load mismatch. Also, the filter you need to design would be an unmatched filter which normally has practical capacitor and inductor availability constraints.

    For such applications that require driving a high impedance ADC, we normally recommend an external resistor in parallel to the 20k resistor which gives an equivalent 100-ohm to 1kohm resistor at the ADC. Also, please note that the LMH6518 has internal 100-ohm differential resistor which will reduce the output swing at the ADC depending upon the equivalent resistor chosen.

    Best Regards,

    Rohit