User Guide

2
-
14 Primer: How to Optimize a Desi
g
n
To start optimizin
g
the diode desi
g
n
1
From the Tune menu, select Auto and click Start.
The PSpice Optimizer performs several simulations. For
each iteration of the parameter values, the optimizer
calculates overall performance and graphically displays the
results. The optimizer also calculates the value of the trace
function, I(d1), and displays the new value in the
specifications area of the PSpice Optimizer window. After
three iterations, the optimizer should converge on a solution
of 4.131 K, as shown in Figure 2-6.
Fi
g
ure 2-6
Optimization Results for the Diode Design
Example
Addin
g
a Constraint and
Rerunnin
g
the PSpice Optimizer
So far, you have optimized for a single goal, Id1. Now suppose
you want to add a condition, or constraint, on the power
dissipated in resistor R1.
Constraints are defined like goals (using the Edit Specification
dialog box) with two additions. In the Internal frame, you must:
• Select the Constraint check box.
• Choose the constraint type (>= target, = target, or, <=
target).
In the diode example, the
derivative at R1=5 k is –1.62 x 10
-7
, or
This indicates that a 1 ohm
increase in R1 will produce a
decrease of 0.162 uA in Id1. To
verify this, try reducin
g
the value
of R1 by 100 ohms (to 4.9 kohm)
and simulate. This increases the
diode current by 16.2 uA and
a
g
rees with the derivative
information.
R1∂
∂
Id() 1.62
7–
×10–=
See The PSpice Optimizer
Window on page 3-5 for a
complete description of the
window elements and how you
can interact with them.