The Subcircuit Definition () feature is used to define subcircuits, which can be inserted as devices into the main circuit using Subcircuit Instance nodes. Create the subcircuit by adding subnodes to the Subcircuit Definition node, either by using the Physics toolbar, or by right-clicking the Subcircuit Definition.

Define the Pin names at which the subcircuit connects to the main circuit or to other subcircuits when referenced by a Subcircuit Instance node. The Pin names refer to circuit nodes in the subcircuit. The order in which the Pin names are defined is the order in which they are referenced by a Subcircuit Instance node. The devices constituting the subcircuit should be connected only to the subcircuit’s pins and to themselves.

To display this section, click the Show More Options button () and select Advanced Physics Options. Specify input parameters to a subcircuit that can be changed from a subcircuit instance. These input parameters can be used in all expression-style edit fields that affect the parameters of a device, for example, resistance, capacitance, and current gain. In this way, a subcircuit can represent a parameterized custom device model.