User`s guide

Cautions and Recommendations for Simulation and Analysis 6

-45

Tradin

Off Computer

Resources For Accurac

It should be clear from the foregoing discussion that there is a

significant trade-off between accuracy and computation time for

parts modeled in the frequency domain. The amount of

computer time and memory scale approximately inversely to

RELTOL. Therefore, if you can use RELTOL=.01 instead of the

default .001, you will be ahead. However, you should first

assure yourself based on the relevant criteria described above

that this will not adversely affect the impulse response. You may

also wish to vary TMAX and TSTOP, since these also come into

play.

Since the trade-off issues are fairly complex, it is advisable to

first simulate a small test circuit containing only the frequency-

domain device, and then after proper validation, proceed to

incorporate it in your larger design. The PSpice A/D defaults

will be appropriate most of the time if accuracy is your main

concern, but it is still worth checking.

Note

Do not set RELTOL to a value above 0.01. This

can seriously compromise the accuracy of your

simulation.