Probes: Fixed vs. Random

Much of this section and some of the next have already been covered in Plotting Simulation Results. It is repeated here for convenience.

SIMetrix provides two approaches to creating plots of simulated results from a schematic.

The first approach is to fix voltage or current probes to the schematic before or during a run. SIMetrix will then generate graphs of the selected voltages and/or currents automatically. Normally the graphs for fixed probes are opened and updated while the simulator is running. The probes have a wide range of options which allow you to specify - for example - how the graphs are organised and when and how often they are updated. These probes are known as fixed probes.

The second approach is to randomly probe the circuit after the run is complete. (You can also do this during a run by pausing first). With this approach, the graph will be created as you point the probe but will not be updated on a new run. These probes are known as random probes.

You do not need to make any decisions on how you wish to probe your circuit before starting the run. You can enter a circuit without any fixed probes, run it, then randomly probe afterwards. Alternatively, you can place a single fixed probe on an obvious point of interest, then randomly probe to investigate the detailed behaviour of your circuit. Note that you can add fixed probes after a run has started but the run must be paused first.

There are many types of fixed probe to suit a range of applications. The random probing method allows you to plot anything you like including device power, FFTs, arbitrary expressions of simulation results and X-Y plots such as Nyquist diagrams. The arbitrary fixed probe provides the same flexibility for fixed probes. See Arbitrary Fixed Probe for details.