eldo_user

Speed and Accuracy
Simulation of Large Circuits
significant impacts. Detailed discussion of these options can be found in “Limiting the
Size of Transient Output Files” on page 353.
See .OPTION OUT_STEP, .OPTION INTERP, .OPTION FREQSMP and .OPTION
OUT_RESOL in the Eldo Reference Manual.
• Use the Periodic Circuit Speedup(PCS) option.
Used to increase the simulation speed for circuits with periodic or nearly periodic
nature. PLLs in near-lock state belong to this category. The amount of speedup depends
on the design nature; the speedup will be more significant with relatively large circuits.
With circuits showing no periodicity at all, the option will not usually provide any
speedup. Periodic Circuit Speedup is invoked by setting PCS=1|2 for BSIM3v3 models
only (PCS=1|2 represent two possible speed optimization methods, PCS=1 is
recommended) or PCS=3 for BSIM4 and BSIM3v3 models (with same speed
optimization as PCS=1). The default is 0. This option only supports the BSIM3v3 and
BSIM4 models.
BSIM4, unlike BSIM3, has many parasitic configurations: gate resistors, body resistors
network, bias dependent access resistors, and so on. These parasitic configurations are
controlled by a set of instance and model parameters (Rdsmod, Rbodymod, and
Rgatemod). As the complexity of the parasitic configuration around the core model
increases, the gain expected by the PCS decreases.
This option should not affect the accuracy of the results.
See .OPTION PCS in the Eldo Reference Manual.
• Try suppressing DC analysis for large digital circuits.
This is achieved by setting the UIC option of the .TRAN command. Very large circuits
are often digital circuits for which an accurate and time-consuming DC analysis may not
be necessary. The logical initialization performed by Eldo prior to any analysis should
ensure that the transient analysis that follows will start with nodes correctly preset.
Initial voltage conditions are specified using the .IC command.
• Decrease the accuracy for MOS digital circuits.
For MOS digital circuits, accuracy can often be decreased to 10mV instead of the
default value of 5mV. This can significantly reduce CPU time.
• Employ the .USE command.
It may be useful to split the circuit into a number of blocks, find DC solutions for each
block, and then find the DC solution of the circuit as a whole using the separate
solutions as a starting point.
Related Topics
Tips for Improving Simulation Performance
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Eldo® User's Manual, 15.3