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Back gate voltage | NMOS | AMS C35B4C3

Hi, I am currently designing an analog circuit and need to change the back gate (bulk) voltage of used MOS transistors. Usually bulk of MOS transistor is connected to VDD (PMOS) or VSS (NMOS). I would like to set bulk voltage Vb to other value, say 2.1 V (while VDD = 3.3 in this technology (AMS C35)). Biasing the bulk of PMOS does not seem to pose a problem, for it is placed in a NTUB (n-well). What about NMOS transistor, that is placed on a substrate (p-type)? Biasing substrate will result in changin the bulk voltage for all transistors in the design. Can I use a N diffiusion layer to isolate chosen NMOS transistors in order to bias their back gate? Is there any other possibility? Kind Regards, piters.

archive over 15 years ago

Hi,
As you state, the NMOS transistors do not sit in their own well in this process so it is not possible to change the bulk voltage. It must be tied to the substrate which is ground.
Cheers,
Roger
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