Analyses

How directives work

Directives are SPICE dot-commands. Add them in the analysis bar at the bottom left of the editor. Each line can be switched on or off without deleting it, and every enabled analysis runs when you press Run.

Numbers take SPICE suffixes, so 1meg, 10k and 100n all work.

.op

Operating point. Solves the DC bias of the circuit with capacitors open and inductors shorted, and reports every node voltage and branch current.

.op

.dc

DC sweep. Steps a source from start to stop and solves the operating point at each value. Use it for transfer curves and I-V characteristics.

.dc <source> <start> <stop> <step>
.dc V1 0 5 0.05

.tran

Transient. Simulates the circuit in time with an adaptive time step. Starts from the operating point unless uic is given, in which case it starts from the initial conditions on capacitors, inductors and .ic nodes. The optional fourth number caps the internal step.

.tran <tstop>
.tran <tstep> <tstop> [tstart] [tmax] [uic]
.tran 5m
.tran 1u 2m 0 1u uic

.ac

Small-signal frequency response, linearised around the operating point. Points are spaced linearly or per decade or octave. At least one source needs an AC magnitude, such as AC 1. Both frequencies must be above zero.

.ac <lin|dec|oct> <points> <fstart> <fstop>
.ac dec 60 10 1meg

.noise

Noise analysis. Reports the output noise density at a node, optionally against a reference node, and the equivalent noise referred to the input source. The frequency grid is written as for .ac.

.noise V(<out>[,<ref>]) <source> <lin|dec|oct> <points> <fstart> <fstop>
.noise V(out) V1 dec 20 10 100k