AC Analysis
How do I plot the input or output impedance of my circuit in AC analysis?
The input and output impedance of the circuit must be plotted in an indirect way. Go under the Component/Analog Primitives/Waveform Sources section. Select the source called I. This is the SPICE independent current source. Place this source across the nodes where you want to measure the impedance. The Value attribute of the I source should be defined as 'AC 1'. This provides a 1A AC current source for AC analysis. Enter AC analysis. In the AC analysis limits, as the YExpression, place the expression:
V(Iname)
where Iname is the Part attribute name of the current source. Since the current is 1A, the voltage across the current source is equivalent to the impedance, so this expression will produce the impedance plot.
