Product Documentation
Spectre AMS Designer and Xcelium Simulator Mixed-Signal User Guide
Product Version 22.09, September 2022

Transient Analysis Statement (tran)

The tran statement computes the transient response of a circuit over the interval from start to stop. The simulator uses the mixed-signal DC steady-state solution as the initial condition unless you use the ic keyword to specify initial conditions. You can specify multiple transient analysis statements in your analog simulation control file.

Name  tran  parameter=value  { parameter=value }

Parameters

You can use the following parameters and values with the tran statement. Values listed in the parameter syntax are the defaults. Unless specifically noted in the definition, you can use these parameters with the Spectre solver only.

Parameter

Definition

annotate=title

Degree of annotation. Values:

no, title, sweep, status, and steps

no

Suppresses information about the tran analysis

title

Produces annotation information such as the number of transient analysis steps and how long the analysis takes.

sweep

status

steps

cmin=0 F

Minimum capacitance from each node to ground.

compression=all

Turns on data compression.

With data compression, the Spectre simulator writes output data for a signal only when the value of that signal changes. This reduces the size of the transient analysis output file for circuits with substantial amounts of signal latency, such as mixed analog and digital designs and circuits with switching power supplies.Values: all, no, wildcardonly

If the compression parameter is set to wildcardonly, and the TCL probe statement contains signals specified with a wildcard or a scope, then the signals specified with the wildcard or the scope are compressed.

probe -create -database waves -all -depth all {testbench.I1.*}
probe -create -database waves -all -depth all {testbench.I2
probe -create -database waves {testbench.I3.net1}
probe -create -database waves {testbench.I4.net2}

In the above example, only the testbench.I1.* and testbench.I2 signals will be compressed.

compfactor=1.0

Compression factor.

Limits the tolerance values during compressing transient waveforms. The compression decision is made according to tolerance * compfactor.

errpreset=moderate

Selects a reasonable collection of parameter settings. Values: conservative, moderate, liberal

fastbreak=no

Specifies the evaluation method to use for VHDL-AMS break statements. Values:

no

Complies strictly with the VHDL-AMS standard

yes

Requests an often faster method, which under some circumstances does not comply with the VHDL-AMS standard

Possible non-compliance with the standard arises when the software associates the break statement with a discontinuity that causes a zero-delay Q'above event. The software might report the Q'above event with a small delay, rather than with a zero delay.

fastcross=cm

Controls whether the AMS Designer simulator uses an optimized cross-detection algorithm for the @above and @cross functions in Verilog-AMS and the ABOVE function in VHDL-AMS. Values:

no

Turns off the optimized algorithm, which you might want to do to verify the behavior and accuracy of models

discrete

Provides better simulation performance by ignoring the unsatisfiable cross tolerance conditions due to discrete or discontinuous signals in the cross signal expression

cm

Includes the features offastcross=discreteand further provides better simulation performance by improving the performance of@aboveand@crossin connect modules (CMs) such as the ConnRules

Possible non-compliance with the standard arises when the software associates the break statement with a discontinuity that causes a zero-delay Q'above event. The software might report the Q'above event with a small delay, rather than with a zero delay.

CMs that Cadence provides

Default Values: (You can override these default values using the fastcross option.)

When errpreset=conservative for the Spectre solver, the default is no.

When errpreset=liberal or moderate for the Spectre solver.

flushofftime (s)

Time to stop flushing outputs.

flushpoints

Flush outputs after number of calculated points.

flushtime (s)

Flush outputs after real time has elapsed.

ic=all

What should be used to set initial condition. Values: dc, node, dev, all

infoname= inf_anal_name

Name of the info analysis to be performed at each time point specified by the infotimes parameter.

infotimes=[...] s

Times when the simulator is to perform the info analysis specified by the infoname parameter.

Setting infotimes to [0] returns the initial transient operating point. Setting infotimes to [stop_time] returns the final transient operating point.

If no value is specified for infotimes, the Spectre solver performs the analysis at time 0.

acnames=[...]

Names of analyses to be performed at each time point in the actimes array. The named small-signal analyses are not run separately, but only as part of the transient analysis.

actimes=[...]

Times when analyses specified in acname array are performed.

lteratio

Ratio used to compute LTE tolerances from Newton tolerance. Default derived from errpreset.

maxiters=5

Maximum number of iterations per time step.

maxstep (s)

Maximum time step. Default derived from errpreset.

method

Integration method. Default derived from errpreset. Values: euler, trap, traponly, gear2, gear2only, trapgear2

oppoint=no

Should operating point information be computed for initial timestep, and if so, where should it be sent. Values: no, screen, logfile, rawfile

outputstart= time

Output is saved only after this time is reached.

readic

File that contains the initial conditions.

readns

File that contains the estimate of initial transient solution.

relref

Reference used for the relative convergence criteria. Default derived from errpreset. Values: pointlocal, alllocal, sigglobal, allglobal

save

Signals to output. Values: all, selected, none

Cadence recommends using the Tcl probe command to save signals instead of the save command since it has fewer restrictions.

skipcount

Save only one of every skipcount points.

skipdc=no

If yes, there will be no DC analysis for transient. If the DC analysis is skipped, the initial solution is either trivial, or given in the file that you specify using the readic parameter. If the readic parameter is not specified, the values specified on the ic statements are considered. Device-based initial conditions are not used for skipdc. Nodes that you do not specify with the ic file or ic statements start at zero. You should not use this parameter unless you are generating a nodeset file for circuits that have trouble in the DC solution.

Values: no, yes, waveless, rampup, autodc

Using the AMS Designer simulator, setting skipdc to anything other than no can cause incorrect signal transitions between analog and digital during transient analysis.

skipstart= starttime s

The time to start skipping output data.

start=0 s

Start time.

stats=no

Analysis statistics. Values: no, yes

step=0.001 (stop-start) s

Minimum time step used by the simulator solely to maintain the aesthetics of the computed waveforms.

stop (s)

Stop time.

strobedelay=0 s

The delay (phase shift) between the skipstart time and the first strobe point.

strobeperiod (s)

The output strobe interval (in seconds of transient time).

title

Analysis title.

transres=resolution s

Duration of a transition below which the simulator stops trying to determine exact times for each corner of a transition and starts handling the two corners as a single event.

write

File to which you want the software to write the initial transient solution.

writefinal

File to which you want the software to write the final transient solution.

Multiple transient analyses are not supported in AMS Designer.

Examples

You run a simulation that uses an analog simulation control file with the following contents.

myopt options rawfmt=psfbin
myinfo info what=oppoint where=rawfile
mytran tran stop=10u infoname=myinfo infotimes=[1u 2u 3u]

The above statements store the operating point data in three different files: timeDom-000_myinfo.info (time:1us), timeDom-001_myinfo.info (time: 2us), timeDom-002_myinfo.info (time: 3us). All three files are placed in the .raw directory.

You run a simulation that uses an analog simulation control file with the following contents.

myopt options rawfmt=psfbin
myinfo info what=oppoint where=rawfile

The above statements store the DC operating point data in a file called myinfo.info located in the .raw directory.

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