eldo_user

Setting Up An Analysis
Improving DC Convergence
.NODESET V=value
Used to help calculate the DC operating point by initializing selected nodes during the first DC
operating point calculation. After the first calculation has been completed, the node values are
released, and a second DC operating point calculation is started. This command is useful when
the whereabouts of the DC operating point is known, enabling Eldo to converge directly to it,
and also for bistable circuits or circuits with more than one operating point.
.GUESS V=value
Enables you to set the initial voltages to specific nodes for the first iteration of a DC operating
point run. This differs from the .NODESET command where the node voltages are fixed for the
duration of the first DC operating point calculation.
.RAMP
This command can be used when no DC operating point has been found using the above
methods. Two ramping facilities are provided: DC ramping and transient ramping.
DC convergence algorithms are automatically used by Eldo when the standard DC algorithm
fails to converge. The sequence of algorithms used is as follows: Newton, Gmin ramping, DC
ramping, Transient ramping, PSTRAN, T° ramping, and DPTRAN. The DPTRAN algorithm is
used as a last attempt at convergence. To disable the automatic convergence aid mechanism,
specify option NOCONVASSIST.
.RAMP_SUPPLY
This command provides a power supply ramping analysis as an alternative to the .RAMP
command. It slowly applies the power range over the specified time value, or over a percentage
of the total simulation duration if the simulation duration is known. This can be used as an
alternative solution when .TRAN UIC is specified.
.OPTION VMIN, VMAX
By default, Eldo looks for the DC operating point within the limits of the circuit power supply.
In the case of a circuit that contains elements that create energy, such as voltage- or currentcontrolled
sources, it is possible that Eldo can look for solutions outside the expected bounds. If
so, Eldo displays the message:
Searching operating point between [x1,x2]
You can control the x1 and x2 limits to speed up the DC convergence process using the VMIN
and VMAX parameters. It must be stressed, however, that unrealistic limits can also cause
convergence problems.
Related Commands
• .GUESS in the Eldo Reference Manual
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Eldo® User's Manual, 15.3