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:
LNA designing help! - 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: LNA designing help! Posted: Sun Aug 07, 2005
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.
Post subject: common gatePosted: Mon Aug 15, 2005 1:28 am
Joined: Mon Aug 15, 2005 12:55 am
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
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 low-enough level.
Uwavegeek is also right about the 1V issue.
It will even be difficult to do a really good job with SiGe or other