Available Gain Circles

And in terms of Circuit Parameters, it can be written as


Since G_out is also a function of G_s, the whole equation depends on G_s.
We can then raise the questions: For what values of G_s, we can obtain the same power gain?
Manipulation of the equation for constant G_a gives a locus of points for G_s on the Smith Chart which lie on a circle.

If we define a parameter

The center and the radius of the circles for constant g_a are given by

Here G_a has to be converted into a number using

The following example gives the constant available gain circles for NE76000 transistor at 10 GHz.
Be patient for the frames to change.