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How to measure transient current in simulation.

RSIDesignEngineer

Hi,

for the active digital block if we want to measure active current with transient simulation then in calculator what function we have to use to measure transient current?

  • Andrew Beckett

    Using the IT() function to measure the current through the pin that you want to measure? Am I missing something here?

    Andrew

  • RSIDesignEngineer
    in reply to Andrew Beckett

    Hi Andrew,
    In lab measurement the active current is 6mA whereas in simulations if I use average function the current value is 26mA.
    simulation and lab measurement value are not matching.
    any suggestions to match lab and simulation results?

  • Andrew Beckett
    in reply to RSIDesignEngineer

    Without more details as to what the circuit looks like, what's being measured in the lab, it's very hard to give an answer with so little information. I suggest you contact customer support (create a case on the support portal) so that an application engineer can work with you to explain how to measure this in your circuit.

    Regards,

    Andrew

  • ShawnLogan
    in reply to Andrew Beckett

    Dear RSIDesignEngineer,

    RSIDesignEngineer said:
    In lab measurement the active current is 6mA whereas in simulations if I use average function the current value is 26mA.
    simulation and lab measurement value are not matching.
    any suggestions to match lab and simulation results?

    As Andrew noted, without a bit more information on your circuit, the nature of your simulation and exact measurement in the lab and in simulation, it is not easy to suggest a reason for the discrepancy. However, I did have a few thoughts and decided  would add them to your post in case they provide any insight to you.

    1.  Does your transient current measurement include any initial time period during which the circuit is settling to a steady-state condition? for example, might some internal capacitors be charging to steady-state values? Your lab measurement may be only a steady-state current value.

    2. Does your circuit contain any inverters configured as shown below to "enforce" the P and N rails of a differential CMOS signal? If so, are you sure the inverters are not both conducting current in your transient simulation? In the lab, the inverters, due to mismatch, may not be conducting and in a logic high/low state.

    3. Are the inputs to your circuit connected to the same logic state as in the lab?

    4. Are the source resistance of all the inputs to your circuit finite and representative of the source resistances in your lab measurement?

    5.  How are you measuring your current in the lab? Are you using a current probe? A DC meter? If a current probe, it may be measuring only AC current. Is the measurement an rms measurement?

    Just a few thoughts for your consideration....

    Shawn

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