# Combination of Subcircuits Circuit Block (Differential)

Use the Combination of Subcircuits Circuit Block Type to define either a measurement or simulation circuit using three blocks instead of one. Select from three arrangements for the three sub-blocks: Cascade Sub-Circuits, Parallel Sub-Circuits, or Series Sub-Circuits.

Once you select the configuration, click on each individual block to open the Sub-Circuit Setup dialog box. You can define each individual block as:

- Thru
- Open
- S-Parameter File
- Unused. Indicates that this particular sub-block is not included in the definition allowing you to use two sub-blocks instead of three. For Cascade sub-circuits, Unused acts like a Thru block. For Parallel sub-circuits, Unused acts like an Open block.

The following tables illustrate the available sub-circuit relationships for four-port devices.

Sub-Circuit Relationships
Relationship | Configuration
--- | ---
Cascaded |
Parallel |
Series |