User Guide

Constrained Optimization 4
-3
When using the PSpice Optimizer, you can set up this problem
in one of three ways:
• Consider V
e
and R
e
as equally important; set up both as
goals.
• Consider V
e
as the most important requirement to meet,
even at the expense of R
e
; set up V
e
as a constraint and R
e
as a goal.
• Consider R
e
as the most important requirement to meet,
even at the expense of V
e
; set up R
e
as a constraint and V
e
as a goal.
Note
Because at least one optimization
g
oal is
necessary, the case where both V
e
and R
e
are
constraints is excluded.
If the problem, like this one, has a solution, the PSpice
Optimizer might arrive at the same answer for all three methods.
However, most problems do not have a single, exact solution as
this one does. For most designs, the result is a compromise that
minimizes the goals while not violating the constraints.
Constrained
Optimization
Many problems in analog circuit optimization are naturally
expressed as the minimization of a function representing a goal
(e.g., power consumption) which is subject to one or more
constraints (e.g., bandwidth). Constraints are typically
complicated nonlinear functions of the parameters of the
problem, so manual optimization is a difficult task.
Most other analog circuit optimizers implement only
unconstrained optimization of a single goal or a sum-of-squares
of several goals. To tackle a problem like the problem outlined
above, other optimizers must combine the functions for the
goals and constraints and then optimize the combination.
Unfortunately, this scheme does not differentiate between
reduction of the goals and violation of the constraints. In