For maximum gain, both input and output ports are conjugately matched
Due to the fact that , the output termination affects input termination and vice versa.
Substitute (126) into (125), we have
Substitute (125) into (126), we have
By the solving (130) and (133), the optimum source termination, , and the optimum load termination, , are found to be
Under the condition that both the input and output termination are conjugated matched, all power gains are equal and they have a value of
It can be shown that
so the maximum stable gain from an amplifier is
Example In a 50 system, a transistor has the following S-parameter at 1.3 GHz.
Find the optimum terminations for maximum power gain.
K= 1.032 > 1 , the transistor is unconditionally stable.