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: LNA designing help! Posted: Sun Aug 07, 2005 9:53 pm
Joined: Tue Aug 02, 2005 1:44 am
Hi, regarding to several topologies of designing
a LNA? The inductive degenation of common source should be the most popular one right now, but the limitation is
the high voltage and not so good isolation. The common gate could be better in applying low voltage and good
isolation, as well as input matching. Why few people use common gate topologies? If I want to design a low
voltage(<1.0v) low power, narrowband RF LNA (abt 2.45GHz), among all the topologies, which could be more suitable
for me to choose? Can you give me some suggestions? Thanks very much.
subject: common gatePosted: Mon Aug 15, 2005 1:28 am
Joined: Mon Aug 15, 2005 12:55 am
My experience with common gate/base LNAs are that they tend to be more unstable than the standard
common source topology. The biasing bypass on the gate/base is very sensitive to parasitic inductances which tend
to be a pain.
You will have a hard time using a FET based technology for under 1V. A bipolar might have a
better chance of working (SiGe).
Post subject: LNAPosted: Mon Aug 15, 2005 11:51
The experience reported by "uwavegeek" matches mine.
However, your thoughts about common-gate
circuits are in fact valid at lower frequencies (VHF/UHF), where you can actually reduce parasitics to a
Uwavegeek is also right about the 1V issue. It will even be difficult to do a really good
job with SiGe or other bipolar technology.