User Guide

Chapter B Convergence and “time step too small errors”
390
Failure at the first time step
If the transient analysis fails at the first time point then
usually there is an unreasonably large capacitor or
inductor. Usually this is due to a typographical error.
Consider the following capacitor:
C 1 3, 0 1Ouf
“1O” (has the letter O) should have been “10.” This
capacitor has a value of one farad, not 10 microfarads. An
easy way to catch these is to use the LIST option (on the
.OPTIONS command).
LIST
The LIST option can echo back all the devices into the
output file that have their values in scientific notation.
That makes it easy to spot any unusual values. This kind
of problem does not show up during the bias point
calculation because capacitors and inductors do not
participate in the bias point.
Similar comments apply to the parasitic capacitance
parameters in transistor (and diode) models. These are
normally echoed to the output file (the NOMOD option
suppresses the echo but the default is to echo). As in the
LIST output, the model parameters are echoed in scientific
notation making it easy to spot unusual values. A further
diagnostic is to ask for the detailed operating bias point
(.TRAN/OP) information.
.TRAN/OP
This lists the small-signal parameters for each
semiconductor device including the calculated parasitic
capacitances.
Pspug.book Page 390 Wednesday, November 11, 1998 1:14 PM