LTC6268-10: Input Capacitance & Input Bias Current in LTspice

Hi!

I couldn't find any answer to two questions regarding Analog's/LT's models in LTspice in general and the model of LTC6268(-10) in particular.

  • Do op amp models already include input capacitance (0.1pF resp 0.45pF for LTC6268-10)?
  • In various configurations, input bias currents are several orders of magnitude higher than specified. How good is the model in this regard?

Of course, spice cannot have perfect accuracy, but it's unclear if the LTC6268-family has a low input bias current in specific situations only – I see up to 500 uA-pp stray input currents oscillating at about 1 GHz and up to 300 pA-pp input currents at the frequencies it's amplifying at.

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  • +1
    •  Analog Employees 
    on Feb 5, 2021 1:40 AM

    Hi ab2:  Yes the models include both CM and DM capacitances.   The model should be excellent w.r.t. bias current, as well as current noises.   If the higher currents you are seeing are not accountable based on the capacitive impedances and frequencies, then there may be clamps in the model that might be kicking in.  You have to consider that at 1GHz, half a pF is 318 Ohms.

Reply
  • +1
    •  Analog Employees 
    on Feb 5, 2021 1:40 AM

    Hi ab2:  Yes the models include both CM and DM capacitances.   The model should be excellent w.r.t. bias current, as well as current noises.   If the higher currents you are seeing are not accountable based on the capacitive impedances and frequencies, then there may be clamps in the model that might be kicking in.  You have to consider that at 1GHz, half a pF is 318 Ohms.

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