Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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My Hobby Website:
Cascade P1dB - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: Cascade P1dB Posted: Mon Oct 01, 2007 7:26
Joined: Tue Sep 04, 2007 7:54 am
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.
Post subject: Posted: Thu Oct 04, 2007 4:31 am
Joined: Tue Mar 15, 2005 11:43 pm
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
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.
hope it helps.
Jean (Wavestream Corp)
Post subject: Posted: Thu Oct 04, 2007 5:58 pm
Joined: Mon Jun 27, 2005 2:02 pm
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.