The Designer's Guide Community
Forum
Welcome, Guest. Please Login or Register. Please follow the Forum guidelines.
May 4th, 2024, 12:34am
Pages: 1
Send Topic Print
RF Buffer for LNA (Read 2723 times)
aaron_do
Senior Fellow
******
Offline



Posts: 1398

RF Buffer for LNA
May 03rd, 2009, 10:39pm
 
Hi all,


just wondering, is this a suitable buffer (see attachment) for characterization of an LNA at 2.4 GHz?

I went for the source-follower instead of common-source in order to get good linearity, and to preserve the shape of the transfer function. My main concern is that the overall gain (DUT + Buffer) is only around 10 dB.  So i'm worried how accurate the noise measurements will be...


thanks,
Aaron
Back to top
 

RFBuffer.jpg

there is no energy in matter other than that received from the environment - Nikola Tesla
View Profile   IP Logged
RFICDUDE
Community Fellow
*****
Offline



Posts: 323

Re: RF Buffer for LNA
Reply #1 - May 7th, 2009, 1:25pm
 
I don't know if the linearity will be that great if the output impedance is going to be 50 ohms. If the source impedance sets the output impedance at resonance, then the voltage swing across Vgs will be the same as the load. You could make the impedance smaller then match up to 50 ohms to help reduce the swing, or you could use some series resistance to help set the output impedance and reduce the voltage dropped across Vgs. Also the SF stage doesn't provide a lot of isolation from the RF output to your LNA load (capacitive coupling). i.e. a SF is not necessarily a no brainer buffer at GHz frequencies.

A resistively or inductively degenerated cascode CS stage buffer might be worth considering.
Back to top
 
 
View Profile   IP Logged
Pages: 1
Send Topic Print
Copyright 2002-2024 Designer’s Guide Consulting, Inc. Designer’s Guide® is a registered trademark of Designer’s Guide Consulting, Inc. All rights reserved. Send comments or questions to editor@designers-guide.org. Consider submitting a paper or model.