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Real-Valued Parameters

abstol
This variable sets the absolute error tolerance used in convergence testing branch currents.

Default Min Value Max Value Set From
1e-12 1e-15 1e-9 Simulation Options/Tolerance

chgtol
This variable sets the minimum charge used when predicting the time step in transient analysis.

Default Min Value Max Value Set From
1e-14 1e-16 1e-12 Simulation Options/Timestep

dcmu
This option variable takes a value of 0.0-0.5, with the default being 0.5. It applies during operating point analysis. When set to a value less than 0.5, the Newton iteration algorithm mixes in some of the previous solution, which can improve convergence. The smaller the value, the larger the mixing. This gives the user another parameter to twiddle when trying to achieve dc convergence.

Default Min Value Max Value Set From
0.5 0.0 0.5 Simulation Options/Convergence

defad
This variable sets the default value for MOS drain diffusion area, and applies to all MOS device models.

Default Min Value Max Value Set From
0.0 0.0 1e-3 Simulation Options/Devices

defas
This sets the default value for MOS source diffusion area, and applies to all MOS device models.

Default Min Value Max Value Set From
0.0 0.0 1e-3 Simulation Options/Devices

defl
This sets the default value for MOS channel length, and applies to all MOS device models. The default is model dependent, and is 100.0 microns for MOS levels 1-3 and 6, and typically 5.0 microns for other models.

Default Min Value Max Value Set From
  0.0 1e4 Simulation Options/Devices

defw
This variable sets the default value for MOS channel width, and applies to all MOS device models. The default is model dependent, and is 100.0 microns for MOS levels 1-3 and 6, and typically 5.0 microns for other models.

Default Min Value Max Value Set From
  0.0 1e4 Simulation Options/Devices

delmin
This can be used to specify the minimum internal time step alowed during transient analysis. When a convergence fails, the internal time step is reduced, and a solution is attempted again. If repeated failures drop the internal timestep below delmin, the run will abort with a ``timestep too small'' message.

If this variable is not set or set to 0.0, WRspice will use 1e-6*tmax. The tmax is the maximum internal timestep which can be specified in the transient analysis specification (.tran syntax), or defaults to tstep, the transient user timestep.

Default Min Value Max Value Set From
0.0 0.0 1.0 Simulation Options/Timestep

It may be counterintuitive, but using a larger delmin may avoid nonconvergence. The matrix elements for reactive terms have the time delta in the denominator, thus these become large for small delta. when delta becomes too small, the matrix elements may become so large that solutions lose accuracy and won't converge. On non-convergence, the time delta is cut, making matters worse and leading to a "timestep too small" error and termination of analysis.

dphimax
This variable sets the maximum allowable phase change of sinusoidal and exponential sources between internal time points in transient analysis.

Consider a circuit consisting of a sinusoidal voltage source driving a resistor network. The internal transient time steps are normally determined from a truncation error estimation from the numerical integration of reactive elements. Since there are no such elements in this case, a large, fixed time step is used. This may not be sufficient to reasonably define the sinusoidal source waveform, so the timestep is cut. This variable sets the time scale for the cut. The default value of $ \pi$/5 provides about 10 points per cycle. All of the built-in source functions that are exponential or sinusoidal reference this variable in the timestep cutting algorithm.

This variable also limits the transient time step when Josephson junction devices are present, i.e., it is equivalent to the jjdphimax variable in Jspice3.

Default Min Value Max Value Set From
$ \pi$/5 $ \pi$/1000 $ \pi$ Simulation Options/Timestep

gmax
The diagonal elements of the circuit matrix are limited to be no larger than a value, which can be set with the gmax option. No normal circuit elements will have conductance near this value, however during iterative solving, large values may be produced by some device models. This can cause non-convergence or the matrix may become singular. By limiting the matrix elements, the problem is avoided.

Default Min Value Max Value Set From
1e6 1e-2 1e12 Simulation Options/Convergence

gmin
This sets the value of gmin, the minimum conductance allowed by the program.

Default Min Value Max Value Set From
1e-12 1e-15 1e-6 Simulation Options/Tolerance

maxdata
This variable sets the maximum allowable memory stored as plot data during an analysis, in kilobytes. The default is 256000. For all analyses except transient with the steptype variable set to ``nousertp'', the run will abort at the beginning if the memory would exceed the limit. Otherwise, the run will end when the limit is reached.

Default Min Value Max Value Set From
256000 1e3 2e9 Simulation Options/General

minbreak
This sets the minimum interval between breakpoints in transient analysis. If this variable is not set or set to 0.0, WRspice will use a value of 5e-8*maxStep, where maxStep may be specified in the transient analysis initiation (.tran syntax), or defaults to (endTime - startTime)/50.

Default Min Value Max Value Set From
0.0 0.0 1.0 Simulation Options/Timestep

pivrel
This variable sets the relative ratio between the largest column entry and an acceptable pivot value. In the numerical pivoting algorithm the allowed minimum pivot value is determined by
epsrel = MAX(pivrel*maxval, pivtol)
where maxval is the maximum element in the column where a pivot is sought (partial pivoting).

Default Min Value Max Value Set From
1e-3 1e-5 1.0 Simulation Options/Tolerance

pivtol
This variable sets the absolute minimum value for a matrix entry to be accepted as a pivot.

Default Min Value Max Value Set From
1e-13 1e-18 1e-9 Simulation Options/Tolerance

rampup
When set to a value dt, during transient analysis all source values are effectively multiplied by pwl(0 0 dt 1). That is, all sources ramp up from zero, and assume their normal values at time = dt.

The dc operating point calculation (if uic is not given) becomes trivial with all sources set to zero.

This is mostly intended for Josephson junction circuits so constant valued sources can be used without convergence problems.

Default Min Value Max Value Set From
0.0 0.0 1.0 Simulation Options/Convergence

reltol
This sets the relative error tolerance used in convergence testing.

Default Min Value Max Value Set From
1e-3 1e-8 1e-2 Simulation Options/Tolerance

temp
This variable specifies the assumed operating temperature of the circuit under simulation.

Default Min Value Max Value Set From
25 -273.15 1e3 Simulation Options/Temperature

tnom
The tnom variable sets the nominal temperature. This is the temperature at which device model parameters are assumed to have been measured.

Default Min Value Max Value Set From
25 -273.15 1e3 Simulation Options/Temperature

trapratio
This controls the ``sensitivity'' of the trapezoid integration convergence test, as described with the trapcheck variable. Higher values make the test less sensitive (and effective) but reduce the number of false positives that can slow down simulation.

Default Min Value Max Value Set From
10.0 2.0 100.0 Simulation Options/Timestep

trtol
This is a factor used during time step prediction in transient analysis. This parameter is an estimate of the factor by which WRspice overestimates the actual truncation error. Larger values will cause WRspice to attempt larger time steps.

Default Min Value Max Value Set From
7.0 1.0 20.0 Simulation Options/Timestep

vntol
This variable sets the absolute voltage error tolerance used in convergence testing.

Default Min Value Max Value Set From
1e-6 1e-9 1e-3 Simulation Options/Tolerance

xmu
This is the trapezoid/Euler mixing parameter that was provided in SPICE2, but not in SPICE3. It effectively provides a mixture of trapezoidal and backward Euler integration, which can be useful if trapezoid integration produces nonconvergence. It applies only when trapezoidal integration is in use, and the maximum order is larger than 1. When xmu is 0.5 (the default), pure trapezoid integration is used. If 0.0, pure backward-Euler (rectangular) integration is used, but the time step predictor still uses the trapezoid formula, so this will not be the same as setting maxord to 1 (which also enforces backward-Euler integration). Trapezoidal integration convergence problems can sometimes be solved by setting xmu to values below 0.5. Setting xmu below about 0.4 is not recommended, better to use Gear integration.

Default Min Value Max Value Set From
0.5 0.0 0.5 Simulation Options/Timestep


next up previous contents index
Next: Integer-Valued Parameters Up: Simulation Option Variables Previous: Simulation Option Variables   Contents   Index
Stephen R. Whiteley 2017-10-02