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Design >> RF Design >> Balun-LNA design
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Message started by prakash@191 on Oct 19^th, 2011, 6:17am

Title: Balun-LNA design
Post by prakash@191 on Oct 19^th, 2011, 6:17am

I have designed balun-LNA using parallel combination of CS and CG stage. My circuit has differential output and single ended input. I matched the input for 50ohms since it is single ended. But my doubt is how to match the differential output for 100ohms.
For output impedance matching, i have separately matched the output for 50ohms assuming virtual ground.(for both outputs of CS and CG buffer stages). After matching i lifted the virtual ground and the output capacitors will come in series. I replaced them with single capacitor ( series combination). I haved used capacitors for matching purpose at the output of buffer stages.

With this setup, i measured S22 by keeping port in between the terminals.
I want to know whether my way of thinking is correct?

Any help would be appreciated

Title: Re: Balun-LNA design
Post by rfcooltools.com on Oct 27^th, 2011, 7:02pm

prakash@191,

I can't exactly picture what you are talking about a simple hand drawing would help.

The concatenating of series components is "legal" for the rough stage of the design process and generally a 100 Ohm port at the output will be useful for calculating part of the performance, but its the most ideal situation. You will want to do more to charectorize other aspects such as common mode stability and performance with an unbalanced load.

http://rfcooltools.com