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LNA designing help! - RF Cafe Forums
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spbhu
Post subject: LNA designing help! Posted: Sun Aug 07, 2005
9:53 pm
Lieutenant
Joined: Tue Aug 02, 2005 1:44 am
Posts: 3
Location: NTU
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.
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uwavegeek
Post subject: common gatePosted: Mon Aug 15, 2005 1:28 am
Captain
Joined: Mon Aug 15, 2005 12:55 am
Posts: 6
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).
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Guest
Post subject: LNAPosted: Mon Aug 15, 2005
11:51 am
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
bipolar technology.
Good Luck!
Posted 11/12/2012
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