Better driver, worse system performance??? - RF Cafe Forums
Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Better driver, worse system performance???
Posted: Thu Jun 03, 2010 6:49 pm
Joined: Mon May 04, 2009
I'm looking for help for a PA design.
My project is a balanced 1W(average) OFDM PA
at 600MHz, droven by a half watt class A driver.
The original design is very close to system requirements,
except marginal fail EVM, which I think caused by
the driver. So I found a drop in replacement driver
and evaluated it. With new match circuits, the new
driver alone performancs very good--2dB higher P1dB
and 1~2dB better EVM.
What confused me is
that system EVM drop by 2~6dB!!
think the driver change would impact the final stage
because there is a 50ohm splitter between them.
Any idea???? Please.
Post subject: Re: Better driver, worse system performance???
Posted: Tue Jun 08, 2010 3:06 pm
Joined: Mon Jun 27, 2005
I think that the problem is not within the driver.
The new driver which you tested proves that
If the problem is linearity - which
seems to be based on the description you showed,
then the problem lies within the balanced amplifier.
The significant stage for cascaded IP3 calculation
is the last stage of the Tx chain.
as the first stage for cascaded NF calculation).
Try to focus on the balanced amplifier and
In many data sheets of power
transistors, there are measured results for different
--> Have you looked on what are
the expected performance of the transistor (within
the balanced amplifier) for the type of signal you
are using (i.e. modulation type, filter applied,
It might be the case that
you need to consider a final stage with more output
More than 10,000 searchable pages indexed.
Your RF Cafe
single-handedly redefining what an engineering website should be.
Progenitor & Webmaster
(Seize the Day!)
My USAF radar shop