Hierarchical Blocks

Note

Generating a subcircuit from a schematic and placing it as an X block with an auto-generated symbol are both implemented. Refining the symbol in a full Symbol Editor and descending into a placed block are still planned; see Placing a block at the end of this chapter.

Hierarchical blocks let a schematic instantiate another schematic as a single subcircuit symbol (device prefix X), the way SLiCAP and SPICE handle .subckt definitions.

Design intent

  • A block is referenced, not flattened, in the capture tool. The netlist keeps the hierarchy (an X instance plus a .subckt definition); SLiCAP / SPICE perform the flattening at analysis time. This keeps netlists small and readable and preserves the design hierarchy.

  • A subcircuit’s interface parameters come from its .subckt definition (name and default value), not from the built-in device tables — matching standard SPICE practice.

  • A block is stored as two artefacts: a netlist (.lib / .subckt) and a symbol, exactly like an ordinary library element, so the same placement and Properties workflow applies.

  • Because symbols and styles are already frozen into a schematic’s sidecar files (see Project Files), a hierarchical design remains portable.

Saving a schematic as a subcircuit

Any schematic can be turned into a reusable subcircuit library:

  1. Add port symbols and name them — the names become the subcircuit’s external nodes. A ground (node 0) stays global and is never a port.

  2. In File ‣ Document Properties…, tick Save this schematic as a SLiCAP subcircuit (.lib) and give the document a Title (the subcircuit name).

  3. File ‣ Save opens the Create Subcircuit dialog, where you set the node order (drag ports up/down — this order is the .subckt node list) and declare the overridable parameters (name and default).

  4. Saving writes both artefacts: the editable source to sch/<title>.slicap_sch and the compiled library to lib/<title>.lib.

The .lib holds one .subckt definition; the ports appear in the chosen order, and a parameter passed in on the .subckt line is not redefined internally — the passed value (or its default) supersedes it. Passed parameters use SLiCAP’s self-referential default idiom, e.g. C_in={C_in}.

Placing a block

Place ‣ Subcircuit… instantiates a saved subcircuit as an X block:

  1. Pick the subcircuit’s .lib. The dialog reads its .subckt header and shows the block name, ordered ports and overridable parameters, and whether a matching sch/<name>.slicap_sch is present.

  2. A default box symbol is generated into lib/<name>.svg — a rectangle with one pin per port, placed clockwise from the top-left in the .subckt node order (so pin order always matches node order).

  3. The block’s .lib is added to the schematic as a .lib include (de-duplicated), and the block is placed like any other component.

In the netlist the block appears as X<n> <nodes…> <name> par=val …: nodes in port order, <name> the subcircuit, and only the parameters you override on the placement. Unset parameters fall back to the .subckt defaults.

Planned

  • Refine the symbol in a full Symbol Editor (the auto-box is a starting point), and choose an existing .svg symbol instead of generating one.

  • Descend hierarchy — open a placed block’s sch/<name>.slicap_sch to edit it.

  • Loop detection across the hierarchy.