> How do you model the power amplifier output impedance? Since a current
> generator of gm.vg in shunt with ra, or -mu.Vg in series with ra is
> inapplicable (let's assume that Class A is NOT under discussion), what is
> your model?
Hi Peter,
You can model the PA that way for matching for matching power
transfer, IF the PA is a type that doesn't change source impedance
with power level or load.
My point is you can not use those models to describe source
behavior since the model does not represent what really happens in
the source. One exception is a lab-type generator that has a large
attenuator on the output. In that case the model describes energy
transfer accurately over a wide load range. Even in that case it
won't describe efficiency. Another case where it describes power
transfer accurately over a "somewhat" wide load range is a class A
PA, or a PA with heavy feedback.
You can not use those models to describe power transfer in
systems where source impedance varies with load impedance, and
that is pretty common, except at one power or load impedance.
They never work to describe efficiency of a complex energy
converter, like a normal HF PA.
73, Tom W8JI
w8ji@contesting.com
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