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Cascade P1dB - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


ljoseph
Post subject: Cascade P1dB Posted: Mon Oct 01, 2007 7:26 am

Captain


Joined: Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
Hi
Is there any general rule of thumb when slecting amplifiers in a chain so that maximum P1dB can be realized from the chain. I know that last stage of the chain should be the highest P1dB amplifier. Curious to know if there any techniques to arrange the amplifiers tio get maximum P1dB.


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Jeanalmira
Post subject: Posted: Thu Oct 04, 2007 4:31 am

General


Joined: Tue Mar 15, 2005 11:43 pm
Posts: 65
Location: Singapore
Hi there,

You are right, for multi-stages power amplifier the largest P1dB should be at the last stage. Or in other words, your last stage should be the largest device with largest current handling capability.

But keep in mind that P1dB is related to the input power too.
So the key is you have to drive enough power (enough gain) to get the correct level of P1dB that you expected.
Besides, to drive high P1dB, you need good matching, especially output matching and interstage matching. Without good interstage-matching, it is difficult to get high P1dB.

Input matching might not be too critical in this case.
Having said that, your preceding stages are as critical as your last stage to determine high P1dB.

I hope it helps.

Regards,
Jean (Wavestream Corp)


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IR
Post subject: Posted: Thu Oct 04, 2007 5:58 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello,

Just to add to the points that Jean mentioned:

You should take care that the stage before the last stage will not get into saturation. In other words, you should drive the amplifier so that only the last stage will be in P1dB. If the first and middle stages will be driven into saturation, you will loose gain and will not reach into the full output power that the amplifier is capable to.







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