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Design >> RF Design >> Linearity
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Message started by uncle_ezra on Jul 21^st, 2005, 2:15am

Title: Linearity
Post by uncle_ezra on Jul 21^st, 2005, 2:15am

As voltage scales down, is linearity worsened for LNA and mixer? Given same circuit one @ 1.8V for 0.15um and another @ 1.5V for 0.13um. Also in LNA, how does the inductor source degeneration affect the linearity?

Title: Re: Linearity
Post by vikas on Jul 27^th, 2005, 10:54pm

As a general notion as you decrease the voltage linearity should degrade. But when constant filed scaling is considered and it can be thought that (vgs- vt) is constant for both technology then linearity should not be much affected.

There are many ways to explain linearity in conjuction with source degeneration. like feedback and gm-linearity. I will try to explain in a simpler way, may be that will do.

If u have a source degenerated common source configuration then source node approximately follows that gate voltage that mean u'll have approximately Vgs acroos the degenration resistor or inductton. this will create a current Vgs/R(impedanc eof source resistor). So now ur drain current is pretty linear in conjuction with Vgs. Now it is just Vgs/R whereas previously it was foloowing a square law characteristic. Further u can also prove that now Gm of the amplifier has become a constant (1/R).. previously it was a fucntion of vgs.

So i think this will explain the linearity issue.