Why do we need large L for mismatch?

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modern_analog

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L effect on mismatch

This might sound very basic but here goes

The mismatch depends on WL, or more accurately 1/sqrt(WL). Then why do we need large L. It seems we can get away with small L and large W.
 

Re: L effect on mismatch

The problem is that if you have a large W you will have a large parasitic capacitance to substrate. At the same time with a lower L the output resistance will be lower. Also a high L reduce the fliker noise.

Bastos
 

Re: L effect on mismatch

Lower L tends to have problem in circuit realibility!

If you are using 0.5um technology...
Try to have bigeer L such as 2@3 times higher that 0.5um

 

Re: L effect on mismatch

1/sqrt(WL) is the mismatch of Vt. If your L is too small, then short channel effect will play a significant role. The Ids will largely depend on Vds.
 

L effect on mismatch

L affect several parameters for a transistor,you must trade off to chose a good one
 

L effect on mismatch

u can increase your L, but keeping W/L = constant .
it will be beneficial to your matching & low noise.(eg, noise which comes from substrate)
 

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