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LM311: input impedance

[FAE] Andrew Wang
Genius 10685 points
Part Number: LM311


Hi Team,

Customer wants to know what is inverting node common mode impedance?

Cannot find this info in datasheet, thx!

Andrew

  • 0
    TI__Genius 17360 points

    Hi Andrew,

    For DC signals, the input resistance can be approximated to Vcm/Ib. Note that the 3pF input capacitance is in parallel to this DC resistance. So as the frequency of the input signal increases, then the reactance of the capacitor (Xc) dominates the resistance seen at the input.

    In shorter terms, low frequency means input resistance is approximately Vcm/Ib. As frequency increases, the input impedance is dominated by the 3pF input cap.

    I hope this helps.

    Regards,

    Joe