problem about the lineanrity of source degenaration

For the below two topology, I thought the linearity of (b) should be better than (a) for there is no body effect. However, the Specture simulation results show that (a) is better than (b). Anyone know why? Thanks

Hello
Upload Your topologies. Pleeeease!

yeah , where are the two schematics

but i can say ur comparing between common source and a commo source with degeration inductor

the degenration inductor , is a feedback elemnt in the RF and this will decrese the gain of ur stage , but it will inhance ur linearity

khouly

sorry, I thought i put on the file, here it is
https://www.edaboard.com/viewtopic.php?p=954101#954101

degeneration is like feedback, you can use your knowledge about feedback :)

you are essentially eliminating your body effect in b). So, given the same current and device size, your Gm is bigger and have more non-linearity effect. The best way is to compare the overall Gm by taking the deviative of the output current vs input voltage, then you will see the difference

no one can explain?

there is nothing to do with the body effect,because the current of a is higher than the b ,so the a better than the b, y can delete the resistor of a