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Speed and Accuracy
Global Tuning of the Accuracy—TUNING
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Speed and Accuracy in Eldo
Global Tuning of the Accuracy—TUNING
Global Tuning of the Accuracy—TUNING
Another global parameter, TUNING, may be used as a general controller to define the accuracy
of a given simulation. With TUNING, the user does not provide numerical values for the
accuracy control switches. Instead, a qualitative flag is specified for the desired accuracy, and
similarly to the effect of EPS, a number of adjustments are activated. Actually, ‘accuracy’ in
this context should be understood as ‘speed/accuracy compromise’.
The TUNING parameter can take four values: FAST, STANDARD, ACCURATE, and
VHIGH.
FAST can be used when the primary concern is to accelerate a simulation, and you are ready to
sacrifice a degree of accuracy to achieve this. The FAST setting is equivalent to EPS=1e-3,
overridden with VNTOL=10e-6, ABSTOL=100e-12, RELTOL=1.25e-3 and CHGTOL=1e-12.
Thus FAST is not entirely equivalent to any given value of EPS. It is an adequate setting if you
are not too worried about picoAmps and nanoVolts accuracy, and your primary requirement is a
short runtime.
STANDARD, ACCURATE, and VHIGH are equivalent to specific values of EPS (see
Table 20-1 on page 1254).
STANDARD corresponds to the Eldo default settings, in other words it is equivalent to setting
EPS=1e-3. If you do not set any option in the netlist file, this is what Eldo will use. Thousands
of test cases covering all possible IC technologies have shown that this is the best compromise
for what Eldo tries to achieve by default—in other words reliable and accurate results in the
shortest CPU time.
Finally ACCURATE and VHIGH (which stands for Very HIGH accuracy) alter the tolerance
switches to achieve higher degrees of accuracy, usually at the expense of longer simulation
times. ACCURATE is equivalent to setting EPS=1e-6, and VHIGH is equivalent to EPS=1e-8.
The VHIGH setting must be used carefully, as it can lead to excessively long simulation times.
It is, however, sometimes necessary, particularly for the cases of the startup phase of sensitive
oscillators.
Note
Using EPS settings smaller than 1e-9/1e-10 is not recommended.
Setting the TUNING flag simply uses the .option mechanism. For example:
.option TUNING=ACCURATE
Eldo® User's Manual, 15.3 1255