Running Simulations

Open the simulation parameters dialog with the Configure toolbar tool (the title is Xyce Simulation). Parameters are organized in a vertical tab bar on the left, grouped by domain:

• DC — .OP, .DC
• Time-domain — .TRAN
• Frequency-domain — .AC, .NOISE, .HB, .LIN

Click OK to apply the settings; the accepted directives are merged into the netlist (before .END) and the simulation runs with them. Cancel, Escape, or the ✕ button closes the dialog and discards changes. Invalid input keeps the dialog open with the error shown in red above the footer buttons.

Tip: clicking Run Simulation with no analysis configured opens this dialog first; the simulation starts after you accept it.

Ground node handling

Every analysis tab offers Replace ground (GND) with 0 (checked by default). When enabled, all GND references in the netlist are replaced with the node name 0 before simulation. This is required by Xyce, which uses 0 as the global ground node. Leave it on unless your netlist already uses 0 for ground.

Time and frequency values

All numeric fields accept standard SPICE engineering suffixes: 1n, 25m, 5u, 10MEG, 1G, ...

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Operating Point (.OP)

The operating point analysis computes the DC bias point of the circuit: all node voltages with the independent sources at their nominal values.

.PRINT output options

Enable .PRINT output to generate a printable output file of the operating point, then select what to include:

Option	Meaning
All voltages V(*)	Every node voltage
All currents I(*)	Every source/device current
Power P(*)	Device power dissipation
BJT leads	BJT lead currents
FET leads	FET lead currents
Additional variables	Free-form list, e.g. V(out) V(in)

• Format — output file format: STD, NOINDEX, PROBE, TECPLOT, RAW, CSV, GNUPLOT, SPLOT. (default) uses the Xyce default (STD). See the Xyce reference guide for format details.
• Output file — optional explicit path for the print file.
• Extra options — additional .PRINT options as KEY=VALUE pairs, e.g. WIDTH=20 PRECISION=12.

Save operating point (.SAVE)

Enable .SAVE operating point to write the converged bias point to a file for reuse in later runs (quick DC convergence of difficult circuits):

• Save as .NODESET / Save as .IC — the file is written as .NODESET or .IC lines.
• Save file — optional output path.
• Level — all or none. Note: if left at (default), Xyce creates no save file.

Convergence hints (.NODESET)

Initial voltage guesses to help the DC solver converge, e.g. V(1)=5.0 V(2)=3.3. Xyce runs two solves: one holding the given values as initial conditions, and one unconstrained starting from that solution. Only voltages can be specified.

Initial conditions (.IC / .DCVOLT)

Conditions enforced for the entire operating-point solve, e.g. V(out)=1.0 V(in)=0. Nodes not listed are free to converge. Only voltages can be specified; unsolvable combinations are possible — see the Xyce Users' Guide for guidance.

• Editing — the Initial Conditions field on the .OP, .DC and .TRAN tabs holds the line exactly as it will be emitted, without the .IC prefix (e.g. V(a)=2 V(b)=10); text that parses to no entry is rejected when the dialog is accepted. The other tabs (.AC, .NOISE, .LIN, .HB) keep the collected statements untouched (pass-through) for now.
• Merge & dedup — every .IC/.DCVOLT statement in the netlist is collected top-down and written back as a single line before .END. A node named by several statements keeps its first position and takes the last value — the order Xyce applies them in — compared case-insensitively, because Xyce uppercases node names.
• Which analyses use it — Xyce consumes .IC in every analysis that computes a DC operating point: .OP, .DC, .TRAN, .AC, .NOISE and .LIN (which rides the AC sweep). With NOOP/UIC on .TRAN the values become the transient starting state and unspecified nodes start at 0. The reference guide documents no effect for .HB.

The .OP tab of the simulation parameters dialog also edits the .OPTIONS NONLIN package values (the operating-point solver controls).

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Transient (.TRAN)

The transient analysis computes the circuit response over an interval of time.

Time stepping

Field	Meaning
Initial step	Initial time step, e.g. 1n. Xyce picks the actual first step as the smallest of this value, the step ceiling, and 1/200th of the time to the next breakpoint.
Final time	Simulation end time, e.g. 1u.
Start time	Optional. Time at which output starts; simulation always begins at t=0 regardless. Defaults to 0.
Max time step	Optional ceiling on the time step. Defaults to (final − start)/10, automatically refined around breakpoints.
OP keyword	NOOP (or its synonym UIC): skip the initial bias-point calculation and start from the specified initial conditions (.IC lines or capacitor IC parameters); unspecified values default to zero. (None) performs the normal bias-point calculation.

Note: unlike classic SPICE, the first number on the .TRAN line is the initial step, not the print interval.

Schedule points

The Schedule points field accepts one time, max_step pair per line, e.g. 1n, 1n. This produces a {schedule(...)} clause: a maximum time step of max_step is enforced while simulation time is between time and the next listed time. A zero or negative step means no enforced limit for that interval.

Directives

• .FFT directives — one per line, e.g. .FFT V(out) START=1n STOP=1u NP=1024. See .FFT syntax below.
• .FOUR directives — one per line, e.g. .FOUR 1e6 V(out). See .FOUR syntax.
• .MEASURE directives — one per line, e.g. .MEASURE TRAN vout_max MAX V(out). See .MEASURE syntax.
• .PLOT directives — one per chart, e.g. .PLOT V(out) abs(I(R1)). They declare the charts the run opens and are not edited here; see The .PLOT Directive.

.PRINT output options

Same options as Operating Point plus a Print type selector: TRAN (normal transient output) or TRANADJOINT (transient adjoint sensitivity output). The print type defaults to TRAN.

The .TRAN tab of the simulation parameters dialog also edits the .OPTIONS TIMEINT, NONLIN-TRAN, LOCA, FFT and OUTPUT package values.

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DC Sweep (.DC)

The DC sweep analysis steps one or more circuit parameters and computes the bias point at each value.

Sweep modes

Mode	Fields	Meaning
LIN	Start, Stop, Step	Linear sweep from start to stop in increments of step. If stop < start, the step must be negative.
DEC	Start, Stop, Points	Logarithmic sweep by decades; Points is the number of points per decade. Stop must be larger than start.
OCT	Start, Stop, Points	Logarithmic sweep by octaves; Points is the number of points per octave. Stop must be larger than start.
LIST	—	Explicit list of values (configured in the nested sweeps table).
DATA	Data table	Sweeps from a .DATA table defined in the netlist.

Nested sweeps

The Add Sweep button appends sweep rows; each row is one nested sweep dimension. A row contains:

• Variable — the swept source/parameter name, e.g. V1, R1, TEMP.
• Start / Stop — sweep range.
• Step (LIN only) or Points (DEC/OCT) or List values (LIST, space-separated, e.g. 0 1 2 5).

Multiple rows produce nested sweeps (all combinations of the outer sweep with each inner sweep).

Validation

The dialog reports errors such as:

• DC DATA sweep requires a data table name
• DC <MODE> sweep requires at least one sweep variable
• per-row errors: sweep variable is required, start value is required, stop value is required, step value is required, points value is required, points value must be a positive integer, start value must be greater than zero.

A rejected OK keeps the dialog open so you can correct the input; Cancel still discards everything.

Directives and .PRINT

• .MEASURE directives as for transient, e.g. .MEASURE DC vout_max MAX V(out).
• Print type: DC or HOMOTOPY; includes the Power option.

Uncertainty quantification (.PCE)

The DC and transient pages carry a shared Uncertainty quantification (.PCE) section (Xyce Reference Guide §2.1.27). .PCE runs a fully intrusive Polynomial Chaos Expansion on top of the .DC or .TRAN analysis: the circuit is evaluated at quadrature points of the distribution and the uncertainty propagates from inputs to outputs.

• Uncertain parameters — one row per sampled parameter with a name (any parameter valid for .STEP), a distribution type and two value fields: uniform → lower/upper bounds, normal → mean/standard deviation, gamma → alpha/beta.
• Expression-based inputs (useExpr) — when enabled, the random inputs come from expression operators such as AGAUSS and AUNIF and the parameter table is ignored.
• .OPTIONS PCES package — one key=value entry per line; the required OUTPUTS entry lists the outputs for which statistics are computed (e.g. OUTPUTS={V(out)}); further entries are COVMATRIX, SAMPLE_TYPE, SEED, OUTPUT_SAMPLE_STATS, RESAMPLE, OUTPUT_PCE_COEFFS, SPARSE_GRID and STDOUTPUT.
• .PRINT PCE output — enables the companion print directive; extra options accept OUTPUT_SAMPLE_STATS=true (mean, meanplus, meanminus, stddev and variance) and OUTPUT_ALL_SAMPLES=true (all quadrature points).

The dialog rejects a PCE configuration with mismatched list lengths or missing distribution values (e.g. PCE parameter R1: a normal distribution requires means) and keeps the dialog open for corrections.

The .DC tab of the simulation parameters dialog also edits the .OPTIONS NONLIN and LOCA package values.

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AC Analysis (.AC)

AC analysis linearizes the circuit around its DC bias point and computes the frequency response over a range of frequencies.

Sweep

Field	Meaning
Sweep mode	LIN (linear), DEC (per decade), OCT (per octave), or DATA (values from a .DATA table).
Points	Number of points per decade/octave (DEC/OCT) or in the sweep (LIN). Integer ≥ 1.
Start / End	Frequency range in Hz, e.g. 1k … 100MEG. End must not be less than start; both must be greater than zero.

Switching the sweep mode clears the fields of the previous mode.

Note: sweeping magnitude and phase of an AC source with DATA is supported, but nonlinear device parameters cannot be swept inside AC analysis — use a .STEP directive for that.

Directives and .PRINT

• .MEASURE directives e.g. .MEASURE AC vout_max MAX V(out).
• Print type: AC or AC_IC (AC initial conditions). Power calculations are not available for AC analysis.

The .AC tab of the simulation parameters dialog also edits the .OPTIONS LINSOL-AC package values.

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Noise (.NOISE)

Noise analysis computes the small-signal noise response of the circuit over a range of frequencies, linearized around the bias point.

Noise configuration

Field	Meaning
Output node	Node where total output noise is measured, e.g. V(out).
Reference node	Optional. Noise is computed as V(output) − V(ref); defaults to ground.
Source name	Name of the independent source the input noise is referred to, e.g. VIN.
Sweep type	LIN, DEC, OCT, or DATA.
Start frequency / End frequency	Frequency range; end must not be less than start, both greater than zero.
Number of points	Points per decade/octave (DEC/OCT) or in the sweep (LIN). Integer ≥ 1.
Data table	.DATA table name (for the DATA sweep type).

Device noise operators

The Device noise operators field accepts one DNI|DNO node source line per requested contribution, e.g. DNI 2 R1 — input-referred (DNI) or output-referred (DNO) noise of a specific device.

Note: noise analysis is a relatively new Xyce feature; not all device noise models are supported. Power is not available for noise analysis. The print type is fixed to NOISE.

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Harmonic Balance (.HB)

Harmonic balance computes the steady-state magnitude and phase of voltages and currents in a nonlinear circuit driven by periodic sources.

Frequency configuration

Field	Meaning
Frequencies	Space-separated fundamental frequencies, e.g. 1e4 2e2.
Harmonics / NUMFREQ	Comma-separated integers selecting the harmonics to solve for.
TAHB	HB time-step schedule values, e.g. 0 1 2 5 10 20.
SELECTHARMS	Harmonic selection, e.g. ALL 1 2 3 5 10.
Startup periods	Number of startup periods simulated before the steady-state solve.

Solver options

• Nonlinear solver options — one KEY=VALUE pair per line, e.g. RHOMAX=1.0.
• Linear solver options — one KEY=VALUE pair per line, e.g. METHOD=KLU.

The available keys are documented in the Xyce reference guide (.OPTIONS NONLIN-HB and .OPTIONS LIN).

Note: time-dependent B sources (and the same restriction applies to E/F/G/H dependent sources in their time-dependent use) do not work with HB analysis. Purely dependent usage works. The print type options are HB (default), HB_FD (frequency domain), and HB_TD (time domain).

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Linear Analysis (.LIN)

Linear analysis performs small-signal parameter extraction and writes the result as a Touchstone file — useful for S/Y/Z-parameter export into RF design tools.

Parameter extraction options

Enable SPARCALC to expose the extraction options:

Field	Meaning
Format	TOUCHSTONE2 (default) or TOUCHSTONE (v1).
Type	Parameter type: S, Y, or Z.
Data format	RI (real–imaginary, default), MA (magnitude–angle in degrees), or DB (magnitude in dB–angle).
Output file	Path of the Touchstone file to write.
Width	Print field width in characters.
Precision	Decimal precision of the data.

AC sweep

The extraction frequencies come from an AC sweep configured here, using the same sweep modes as AC Analysis: LIN, DEC, OCT, or DATA with Points/Start/End or a data table.

Note: with SPARCALC enabled, the .LIN analysis is done at the frequency values specified on the .AC line. The print type is fixed to AC; Power is available.

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Print output options

All analysis tabs that produce waveform output share the .PRINT card:

• Enable .PRINT output — turn printing on.
• Variable selection — All voltages V(*), All currents I(*), Power P(*), BJT leads, FET leads (availability varies by analysis), plus Additional variables as a free-form list.
• Format — STD, NOINDEX, PROBE, TECPLOT, RAW, CSV, GNUPLOT, SPLOT.
• Output file — optional explicit file path.
• Extra options — additional KEY=VALUE pairs (e.g. WIDTH=20 PRECISION=12).

Xyce Studio can plot all simulation output: the charts panel reads the print file produced by the run in any plottable format — RAW (.raw), PROBE (.csd), CSV (.csv), TECPLOT (.dat) and the .prn formats (STD, NOINDEX, GNUPLOT, SPLOT). Therefore:

• always enable .PRINT output for the analysis you are running, and
• keep the Format on any plottable value — (default) (STD) works.

Without a .PRINT line the run may complete but produce nothing plottable, and the charts panel will stay empty.

To declare the charts a run should open, add .PLOT directives to the netlist — they also make the run print the quantities they plot, so a .PRINT line is no longer needed just to get something on screen.

Options

Xyce Studio splits the managed .OPTIONS packages by the simulation they apply to:

• The Options toolbar tool (right after Configure) edits the simulation-agnostic packages: DEVICE, LINSOL, PARSER, DIAGNOSTIC, DIST, MEASURE and RESTART.
• The simulation-specific packages are edited in the Configure dialog on the tab of their analysis: TIMEINT, NONLIN-TRAN, FFT and OUTPUT on .TRAN; NONLIN on .OP and .DC; LOCA on .DC and .TRAN; LINSOL-AC on .AC.

Section	Option parameters	Simulation type
DEVICE	DEFAD, DEFAS, DEFL, DEFW, DIGINITSTATE, GMIN, MINRES, MINCAP, TEMP, TNOM, NUMJAC, VOLTLIM, B3SOIVOLTLIM, B3SOIGMINSCALING, ICFAC, MAXTIMESTEP, SMOOTHBSRC, RCCONST, VDSSCALEMIN, VGSTCONST, LENGTH0, WIDTH0, TOX0, DEBUGLEVEL, DEBUGMINTIMESTEP, DEBUGMAXTIMESTEP, DEBUGMINTIME, DEBUGMAXTIME	General
TIMEINT	METHOD, RELTOL, ABSTOL, RESTARTSTEPSCALE, NLNEARCONV, NLSMALLUPDATE, RESETTRANNLS, MAXORD, MINORD, NEWLTE, NEWBPSTEPPING, MASKIVARS, ERROPTION, NLMIN, NLMAX, DELMAX, MINTIMESTEPSBP, TIMESTEPSREVERSAL, DOUBLEDCOPSTEP, BREAKPOINTS, BPENABLE, EXITTIME, EXITSTEP	Transient (.TRAN)
NONLIN	NOX, NLSTRATEGY, SEARCHMETHOD, CONTINUATION, ABSTOL, RELTOL, DELTAXTOL, RHSTOL, SMALLUPDATETOL, MAXSTEP, MAXSEARCHSTEP, IN_FORCING, AZ_TOL, RECOVERYSTEPTYPE, RECOVERYSTEP, DEBUGLEVEL, DEBUGMINTIMESTEP, DEBUGMAXTIMESTEP, DEBUGMINTIME, DEBUGMAXTIME	DC / operating point
NONLIN-TRAN	same keys as NONLIN	Transient (.TRAN)
LINSOL	TYPE, PREC_TYPE, USE_AZTEC_PRECOND, USE_IFPACK_FACTORY, IFPACK_TYPE, SHYLU_RTHRESH, TR_PARTITION, TR_PARTITION_TYPE, TR_SINGLETON_FILTER, TR_AMD, TR_GLOBAL_BTF, TR_REINDEX, TR_SOLVERMAP, ADAPTIVE_SOLVE, AZ_MAX_ITER, AZ_PRECOND, AZ_SOLVER, AZ_CONV, AZ_PRE_CALC, AZ_KEEP_INFO, AZ_ORTHOG, AZ_SUBDOMAIN_SOLVE, AZ_ILUT_FILL, AZ_DROP, AZ_REORDER, AZ_SCALING, AZ_KSPACE, AZ_TOL, AZ_OUTPUT, AZ_DIAGNOSTICS, AZ_OVERLAP, AZ_RTHRESH, AZ_ATHRESH, OUTPUT_LS, OUTPUT_BASE_LS, OUTPUT_FAILED_LS	General
LINSOL-AC	same keys as LINSOL	AC (.AC)
LOCA	STEPPER, PREDICTOR, STEPCONTROL, CONPARAM, INITIALVALUE, MINVALUE, MAXVALUE, BIFPARAM, MAXSTEPS, MAXNLITERS, INITIALSTEPSIZE, MINSTEPSIZE, MAXSTEPSIZE, AGGRESSIVENESS, RESIDUALCONDUCTANCE	DC / transient (continuation)
PARSER	MODEL_BINNING, SCALE	General
DIAGNOSTIC	EXTREMA, EXTREMALIMIT, VOLTAGELIMIT, CURRENTLIMIT, DISCLIMIT, DIAGFILENAME	General
DIST	STRATEGY	General
MEASURE	DEFAULT_VAL, MEASDGT, MEASFAIL, MEASOUT, MEASPRINT, USE_CONT_FILES, USE_LTTM	General
FFT	FFT_ACCURATE, FFTOUT, FFT_MODE	Transient (.TRAN)
OUTPUT	INITIAL_INTERVAL, OUTPUTTIMEPOINTS, PRINTHEADER, PRINTFOOTER, SNAPSHOTS, ADD_STEPNUM_COL, PHASE_OUTPUT_RADIANS	Transient (.TRAN)
RESTART	PACK, JOB, INITIAL_INTERVAL, FILE, START_TIME	General
SAMPLES	NUMSAMPLES, SAMPLE_TYPE, OUTPUTS, MEASURES, COVMATRIX, SEED, OUTPUT_SAMPLE_STATS, REGRESSION_PCE, PROJECTION_PCE, RESAMPLE, OUTPUT_PCE_COEFFS, SPARSE_GRID, STDOUTPUT	Sampling (.SAMPLING)
EMBEDDEDSAMPLES	NUMSAMPLES, SAMPLE_TYPE, OUTPUTS, COVMATRIX, SEED, OUTPUT_SAMPLE_STATS, REGRESSION_PCE, PROJECTION_PCE, RESAMPLE, OUTPUT_PCE_COEFFS, SPARSE_GRID, STDOUTPUT	Embedded sampling

In both dialogs, every option Xyce documents for the package (Reference Guide §2.1.25) is listed as a row, whether or not the netlist uses it yet; keys the netlist carries but the catalog does not document are appended as extra rows. Options with a closed set of values (e.g. METHOD = trap/gear) render a combobox with a <default> entry that clears the option, free-text fields show the guide's default value as placeholder, and bare flags (a key written without a value, e.g. .OPTIONS FFT FFTOUT) offer a flag is set entry that keeps them, while <default> removes the option. On accept, valued options are written back as .OPTIONS <PKG> KEY=VALUE lines, kept bare flags as a bare KEY, and every other empty field omits the option. Both dialogs parse the options from the netlist when they open and leave the configured analysis untouched.

The HB solver options (HBINT, NONLIN-HB, LINSOL-HB), the PCE options (PCES) and the sensitivity options (SENSITIVITY) are edited in their own analysis panels. The sampling options (SAMPLES, EMBEDDEDSAMPLES) belong to .SAMPLING/.EMBEDDEDSAMPLING statements, which Xyce Studio does not manage — their netlist values are preserved but not editable. Standalone .OPTIONS lines without a package keyword are not managed and stay verbatim in the netlist text.

Directives

.FFT directives

.FFT <output> [NP=<value>] [WINDOW=<value>] [ALFA=<value>]
     [FORMAT=<value>] [START=<value>] [STOP=<value>]

• <output> — the signal to transform, e.g. V(out), I(L1).
• NP — number of FFT points, rounded to a power of two, minimum 4, default 1024.
• WINDOW — windowing function: RECT (rectangular, default), BART (Bartlett), BARTLETTHANN, BLACK/BLACKMAN, HAMM/HAMMING, HANN/HANNING.
• START/STOP — restrict the transform to a time range.

.FOUR directives

.FOUR <freq> <output> [output]*

Performs Fourier analysis over the last period (1/freq) of the transient simulation and reports the DC component and the first nine harmonics. Results are written to <netlist>.four# files.

.MEASURE directives

.MEASURE <AC|DC|NOISE|TRAN> <result name> <type> <variable> [FROM=...] [TO=...]

Common measure types:

Type	Meaning
AVG	Average of the variable over the interval
MAX / MIN	Maximum / minimum value
RMS	Root-mean-square value
PP	Peak-to-peak value
INTEG	Integral of the variable
FIND ... AT=<value>	Value of the variable at a specific time/frequency
WHEN <var>=<value>	Time/frequency at which the variable crosses a value
TRIG / TARG	Rise/fall propagation measurements

Results are printed to the output log (visible in the Simulation Output panel).

Measurements can be restricted with FROM=<value> and TO=<value>, and expressions may reference .PARAM variables. The full syntax — including FRAC_MAX, TD, error measures, and WHEN crossing variants — is in the Xyce reference guide.