loose-electron
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Best Design Tool = Capable Designers
Posts: 1638
San Diego California
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What is the motivation for doing this? You wont get better matching, since you are still using the shorter channel devices. If you just want to get a 2*L effect, then (for NMOS, with the bottom transistor grounded) then the two devices should share a common substrate node and that gets tied to ground.
But with the above, why not just make the transistor have a L = 2X what it was to do the same thing?
If you are trying to do something where the top transistor (NMOS example still) has less body effect, then tie the body to it's source. However, if it is P-substrate, N-well CMOS, you dont have that freedom. They are all on the same substrate.
If the example twists to a PMOS device where you DO have control of the substrate, then you can tie the well to the source. BUT when you start doing layout on this, the design rules associated with wells wil make the layiut get big very quickly, and you will probably want to put them in a common well to save space.
Lots of possibles here.
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