Making impedance measurements in SPICE
Article By : John Dunn
You can make impedance measurements using the Bode analyzer, an AC current source, and a current probe.
The collection of test instruments in the Multisim SPICE version that I’ve been using does not include an impedance measurement tool. However, one can make such a tool using the Bode analyzer, an AC current source, and a current probe. Three impedance measurement examples are seen in the following sketch.
Figure 1 Impedance magnitude measurements using linear impedance scaling and logarithmic frequency scaling
This works by using the IN port of the Bode analyzer to monitor the input current to the test subject while the OUT port monitors the resultant voltage. The analyzer delivers a display of the ratio of OUT divided by IN which is the test subject’s impedance.
Figure 2 Impedance magnitude measurements using logarithmic impedance scaling and logarithmic frequency scaling
Magnitude and phase can each be examined with the Bode analyzer set for linear or logarithmic scaling. Some examples are as follows.
Figure 3 Impedance phase measurements using linear phase scaling and logarithmic frequency scaling
Figure 4 Impedance magnitude measurements using linear impedance scaling and linear frequency scaling
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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