Impedances in LT-spice - diyAudio
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Old 24th March 2012, 07:13 PM   #1
MiiB is offline MiiB  Denmark
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Join Date: May 2005
Location: Denmark
Default Impedances in LT-spice

I have been using LT-spice for quite a while and do get good and reliable results. But I would surely like to extend my analysis capabilities.
For one i would like to know how to do math functions like plotting U/I for getting a view on input impedance...I would also like to find a method for calculating or plotting output impedances of my circuits. This could be handy for analyzing different current-sources and current mirrors..

If you know-how..please chip in..
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Old 25th March 2012, 12:49 AM   #2
jcx is online now jcx  United States
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1st always wring out circuit DC bias, linear operation limits in .TRAN


then you can use .AC for some limited validity tests that rely on the "linearized" properties of the circuit - remember no "sim" is going on in .AC analysis - no clipping, saturation effects are shown

but these tests can include ratioing V/I in "Cartesian" plot mode the vertical display will read in Ohms

to test CCS terminate in a Vsource with AC=1 set, run .AC frequency sweep and plot the Vsource V/I

for a amp's output Z add a spice Isource with AC=1 to the output, again plot the source V/I


in .TRAN you can do single frequency tests with sine sources, I use fft and cursors to get I, V mag, phase of the test sources
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