the connection between the ground and the subtrate

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hellotxn

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I use GeSi BiCmos 0.35 process to design some circuit. I feel confused about the connection between the component subtrate and the ground. Someone tell me that I shoud conncet the subtrate of the npn or mos transitor to the ground. but someone tell me they did not do so. I want to know the connection between the ground and the subtrate is necessary or optional. And how to know what kind of subtrate of under a type of transistor.

Thanks!
 


the substrate type is important. n type connect supply , p type connect ground
 

Substrate- the most common subtrate is a lighly doped P type substrate ask the fab what tyoe they use. An N tyoe substrate is not common as it is more expensive..
N-Well is diffused into the substrate ( used for p type devices connected to any supply/signal) and nmos devices are connected to the P substrate which is grounded.. Substrate is simply p type diffusion connected to the P type substrate.
 

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