Impedance Plot Analysis

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Description

An Impedance Plot analysis shows the impedance seen by any two-terminal source in the circuit.

Setup

An Impedance Plot does not have a separate setup page of its own and is normally run and plotted as part of an AC Small Signal analysis.

To include Impedance Plot analysis results in an AC Small Signal analysis, ensure that the Collect Data For field on the General Setup page of the Analyses Setup dialog, is set to one of the following:

  • Node Voltage, Supply and Device Current
  • Node Voltage, Supply Current, Device Current and Power
  • Node Voltage, Supply Current and Subcircuit VARs
  • Active Signals

Locate the source of interest in the Available Signals list and add it to the Active Signals list. The signal will appear with a [z] suffix, indicating that it is an impedance-based signal. For example, a source in the circuit with the designator VIn, would appear in the Available Signals list as VIn[z].

Notes

The impedance measurement is calculated from the voltage at the supply's positive terminal, divided by the current out of that same terminal.

To obtain an impedance plot of the circuit's output impedance, follow these steps:

  • Remove the source from the input.
  • Ground the circuit's inputs where the input supply was connected.
  • Remove any load connected to the circuit.
  • Connect a two-terminal source to the output, with the source's positive terminal connected to the output and its negative terminal connected to ground.
  • Setup the signals of interest as described previously and run the simulation.

The simulation results are displayed on the AC Analysis tab of the Waveform Analysis window.

Examples

Consider the circuit in the above image, where an AC Small Signal analysis is to be run. To obtain an Impedance Plot analysis of the source VIN, the signal VIN[z] is taken across into the Active Signals list on the General Setup page of the Analyses Setup dialog.

Running the simulation yields the impedance plot shown in the image below:

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