When referencing another probe as a negative reference probe, the primary probe acts as a differential probe with respect to the reference probe. The probe variables in analysis-based simulations, such as AC Sweep, and probe parameters in interactive simulation assume an underlying differential measurement.

A Current Probe can reference only another Current Probe, but a Voltage Probe can reference another Voltage Probe as well as a special probe called the Voltage Reference Probe, shown below:

This probe is designed to act only as reference for a voltage probe. It does not make any measurements on its own. It is analogous to the alligator clip on a real oscilloscope probe.

  Select the reference probes from a Voltage or Current probe's properties dialog box.

In the example below, PR1 has PR3 selected as its Negative reference probe. Note that PR1's symbol has an added “+” as well as a “+ -” icon referencing PR3: