Zsopt invarianve with source degeneration

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john.zhang

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Hi all,

I am currently designing a simple LNA, and I have come across the statement that Zsopt does not change with the addition of a source degeneration Inductor.

I heard the explanation that this is because Zsopt is invariant to lossless impedance transformations. However, when I try to simulate Zsopt vs Ls (the degeneration inductor) in a simple cascode with CS input LNA using all ideal components, the Zsopt is also affected. Why is this so?

Also, do you guys know any good textbooks on this matter?

Many thanks!
 

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