Re: Matching source and input impedances in power amplifiers

Maximum power is always transferred when Zo = Zl.

That doesn't mean it's best.. most audio equipment has Zl >> Zo, and
speakers handle best when Zl >> Zo; amplifiers tend to go "poof" when Zl ~
Zo!.

RF equipment is (always?) designed to accommodate this matched condition,
primarily for two reasons (that I can think of): power efficiency, and
mismatched loads cause nasties on your line, namely reflections (manifest as
SWR).

BTW, you would want Zin higher than Zs, otherwise your voltage disappears
(and most equipment is voltage-sensitive).

As for power delivered to the *load*, more power will be delivered IFF the
power amplifier is still linear. If it's saturated, more drive isn't going
to do anything.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

<theduder2005@xxxxxxxxx> wrote in message
news:1150852255.387458.116160@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi.

I have a question concerning impedance matching in RF power amplifiers.

Given a power amplifier with input impedance Zin and output impedance
Zo, a source with impedance Zs and a load Zl - does conjugate matching
Zin and Zs give the highest output power?

I know that matching Zo to Zl will transfer the most power to the load,
but shouldn't Zin be much greater than Zs so the amplifier "sees" the
whole input signal? (ignoring reflections and noise performance)

Regards



.

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