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Input matching of common-source LNA (with small Cgs) (Read 169 times)
Berti-2
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Input matching of common-source LNA (with small Cgs)
Jul 13th, 2017, 10:57pm
 
Hi all,

I am working on a common-source LNA with inductive degeneration.
For the input matching, I followed the standard approach:
Set the real part of the input impedance (Ldeg*gm/Cgs) to 50Ohm and then try to cancel the imaginary part (Cgs*(Lg+Ldeg)*w2-1)/Cgs*w with a series inductor Lg .

In my design, Cgs is very small (~15fF)  which results in a large Lg (>100nH).
Can I do something to obtain more reasonable Lg?

Thanks!
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Jacki
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Re: Input matching of common-source LNA (with small Cgs)
Reply #1 - Jul 18th, 2017, 6:23am
 
you can put a Cp (parallel capacitor with your common source transistor) to increase the Cgs artificially.
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Berti-2
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Re: Input matching of common-source LNA (with small Cgs)
Reply #2 - Jul 18th, 2017, 11:02pm
 
Thanks. I found the same statement in Razavi's RF microelectronics book Smiley
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