Hi,
I am newbie in RF IC design and presently working to design an LNA at 2.4GHz.I have a doubt .I used a cascode arrangement with current mirror for biasing.the problem is once I did the dc analysis and printed the dc operating point in cadence virtuso(UMC 180nm tech) the value obtained for Cgs=-124.3f and gm=34.74m.the transition frequency ,wt=gm/Cgs=279G .is this value very large since Ls=Rin/wt and if Rin=50ohm,Ls will be 0.179nH !!!!
where shall be the mistake?????
First, ft=gm/Cgs, and therefore Ls = 50/(6.28*279G) = 28.5 pH
Second, seems like you got wrong value for Cgs, i measured Cgs for transistor in 65 nm technology with gm = 34m and it equal 270 fF.
If value of Ls very small, one of possibilities is decreasing ft of transistor with additional capacitor or increasing channel length.
First, ft=gm/Cgs, and therefore Ls = 50/(6.28*279G) = 28.5 pH
Second, seems like you got wrong value for Cgs, i measured Cgs for transistor in 65 nm technology with gm = 34m and it equal 270 fF.
If value of Ls very small, one of possibilities is decreasing ft of transistor with additional capacitor or increasing channel length.
I don't use for measuring the dc operation point window, it's look strange
For gm you can use dc sweep for input voltage, and then plot gm from direct plot form. For Cgs i run AC analysis and mesure capacitance in it.
I don't use for measuring the dc operation point window, it's look strange
For gm you can use dc sweep for input voltage, and then plot gm from direct plot form. For Cgs i run AC analysis and mesure capacitance in it.
DC operation point also giving gm, but is it correct? When i measure gm with sweep input voltage it gives another results.
I can't explain why this values is different, but i think that there is more experienced people who can give answer for you.
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DC operation point also giving gm, but is it correct? When i measure gm with sweep input voltage it gives another results.
I can't explain why this values is different, but i think that there is more experienced people who can give answer for you.