eldo_user

Optimization
Robust Optimization Using Corners
This example illustrates the combination of optimization and .ALTER commands. For this
purpose a new architecture based on the concepts of multi-context of simulation and multinetlist
optimization has been developed.
Nominal optimization focuses on finding the best design variable values for one nominal
operating condition of the circuit. Typically the power supply, the ambient temperature, and the
process technology are given their nominal value, and the best value of design variables is
found by the optimizer.
However, if the circuit has to operate under a variety of operating conditions, nothing
guarantees that these will always be optimal design variable values if they are simply set to
these optimal nominal values. Maybe if the power supply level is slightly changed, the circuit
will fail.
Robust optimization focuses on finding the set of design variable values that fulfill the
specifications across a certain range of operating conditions. For example, robust optimization
would be performed on a circuit that must operate between 1.7 and 1.9V, a temperature range of
-25C to 100C, and accommodate variations in the process (defined by the corner device model
libraries). The optimization targets might have upper or lower bounds on certain characteristics
(for example the DC consumption has to be lower than 50μA, in all operating conditions). They
might be set as targets for the average value of a given specification.
Operating conditions are defined with .ALTER commands in Eldo. In each .ALTER command
the operating conditions (typically the power supply level and the temperature) and the corner
device model library, are defined. The optimization commands (design variables definition,
design objective definitions, and the optimize command) from the main netlist are then
interpreted to span the main netlist conditions and the various combinations defined through the
.ALTER sections.
Note
These types of optimizations are usually more costly than simple nominal optimizations.
Eldo can distribute the simulations on multi-processor machines to accelerate the process.
Circuit Statements
The following netlist is available in the directory $MGC_AMS_HOME/examples/optimizer
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Eldo® User's Manual, 15.3