Component Properties

Double-click a placed component (or select it and open its context action) to edit its properties.

The Properties dialog

Fig. 32 The Properties dialog: description and documentation link at the top, then the reference designator, model, parameters and orientation.

Reference designator

The refdes is the element’s unique name on the schematic (R1, C3, N1 …). It becomes the element name in the netlist.

Model

Each symbol carries a SLiCAP model name. It is shown for reference and is written into the netlist.

Parameters

The parameter rows are the values you can set for the element — for example a resistor’s value, or a source’s dc and noise. The available parameters come from the symbol itself.

  • Enter a number (1k, 2.2e-9) or a symbolic expression wrapped in braces, e.g. {R_s} or {1/(2*pi*R*C)}.

  • Braced expressions are typeset through LaTeX on the canvas (when pdflatex and dvisvgm are available); otherwise they are shown as plain text.

Value notation (scale factors)

All values entered in the GUI — component values, parameters, and the fields of the instruction dialogs — use SLiCAP notation. Scale factors are case-sensitive:

y = 1e-24

z = 1e-21

a = 1e-18

f = 1e-15

p = 1e-12

n = 1e-9

u = 1e-6

m = 1e-3 (milli)

k = 1e3

M = 1e6 (mega)

G = 1e9

T = 1e12

P = 1e15

NGspice schematics

NGspice itself reads scale factors case-insensitively (m and M are milli; mega is Meg). You still enter SLiCAP notation — SLiCAP translates automatically wherever values are written into NGspice input (netlists, .param lines, instruction arguments): 1M becomes 1Meg, and suffixes NGspice does not know (y, z, a, P) are expanded numerically. The only exception is numeric literals inside hand-written brace expressions like {2.2k/R}: these are passed to NGspice untouched, so use exponent notation (2.2e3) or NGspice notation there.

References

Some elements reference another element — for example a current-controlled source (H/F) names the voltage source whose current it senses, and a coupling factor K names the two inductors it couples. These appear as ref rows.

Showing and hiding labels

For each property there are two check-boxes:

  • Show value — draw a label for this property on the canvas.

  • Show name — prefix the value with its name (value: 1k instead of 1k). Only available when Show value is on.

Labels you switch on can be dragged to any position around the symbol; a thin dashed leader line connects a label to its component while it is selected.

Orientation

The lower part of the dialog sets:

  • Rotation — 0°, 90°, 180° or 270°.

  • Mirror horizontal / vertical — flip the symbol.

Labels stay upright and readable regardless of the symbol’s orientation.

DC operating-point annotation (NGspice)

On NGspice schematics, independent voltage sources and inductors offer a Show DC operating current check-box in their Properties dialog, and the Net Label dialog (double-click a wire) offers Show DC operating voltage. Checking them places an I: <value> / V: <value> text on the canvas.

The values come from the circuit’s most recent unstepped operating-point run (sl.op(...) in the instruction file, which writes cir/<circuit>_op.raw); they are updated after every run, shown greyed and italic while no results are available (V: —) or after the schematic was edited (stale), and are never stored in the schematic file — only the check-box and the label position are.

Currents follow the NGspice sign convention: I(V...) and I(L...) are measured into the positive terminal, so a source that delivers current to the circuit reads negative. A 0 V voltage source in series with a branch therefore acts as an ammeter for that branch.

Colour, font, and the number of digits are set in the schematic preferences under Bias annotation (engineering notation with SLiCAP scale factors, e.g. 1.23m).