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Subject: Re: Analog CMOS Design

Date: 02/04/01 at 10:32 PM
Posted by: Cm
E-mail: tancming@yahoo.com
Message Posted:

In Reply to: Re: Analog CMOS Design posted by siswoyo edo on 02/04/01 at 11:14 AM:

When the body(backgate) is tied to Vdd/Gnd(depending on whether substrate is P or N sub) instead of to the source, the Vth of the MOS will be increased meaning that it will be more difficult to turn on. the relationship is given
as below.

Vth=Vt0 + gamma(sqrt(phi-Vbs) -sqrt(phi))
Vt0 - threshold voltage for Vbs=0
gamma - bulk threshold parameter
phi - strong inversion surface potential
Vbs - backgate to source voltage

In normal applications, Vt0, gamma and phi are fixed as constants leaving only Vbs to change. As Vbs change the MOS will have different Vth.


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