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separating out capacitive currents in transistors (Read 3240 times)
madsoup
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separating out capacitive currents in transistors
Feb 18th, 2009, 6:22pm
 
i'm trying to directly measure in spice where the currents entering the terminals of a transistor flow.  specifically, i want to be able to differentiate between currents charging capacitances and other.

the path i'm heading down is breaking apart one of the verilog-a transistor models, making a standalone verilog module for each of its current sources and then wiring them up in a schematic.  this way i can  descend into the transistor and probe internal branches.

i've been eyeing the models at SIMUCAD, and i also have the "official" EKV2.6 model from the EKV guys.  

good idea, bad idea, general thoughts?

thanks


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« Last Edit: Feb 18th, 2009, 11:06pm by madsoup »  
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Geoffrey_Coram
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Re: separating out capacitive currents in transistors
Reply #1 - Feb 24th, 2009, 6:13am
 
Many of the transistor models will break out op-pt info such as the channel or diode currents; subtracting these from the total terminal current might give you what you want.

Your approach might work; it will almost certainly be inefficient because certain calculations are used in several internal equations.
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madsoup
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Re: separating out capacitive currents in transistors
Reply #2 - Feb 28th, 2009, 10:09pm
 
actually, something like that would work just fine for what i want.

is there a straight forward way to have spice (i mostly use hspice, and spectre, though i am not opposed to other simulators) spit out sorta quasi-steady-state voltages and currents from a time simulation?

to be more specific, what i'd want would be the equivalent functionality of taking take all node voltages as a function of time from a transient simulation.  then use these in a parametric dc sweep to get the currents.

this would be even better, as i wouldn't have to limit myself to only veriloga models.
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Ken Kundert
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Re: separating out capacitive currents in transistors
Reply #3 - Mar 1st, 2009, 12:10am
 
With spectre, add "save M1:displacement" to your netlist, where M1 should be replaced with the name of the component that you want the capacitive currents for, and it will save the displacement (capacitive) currents to the rawfile. They you will need to need to bring up the results browser and manually plot these currents.

-Ken
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madsoup
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Re: separating out capacitive currents in transistors
Reply #4 - Mar 2nd, 2009, 12:19am
 
excellent, this is exactly what i was looking for.

thank you guys so much.
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