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A question about capacitance between gate and source

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A question about Cgs.

when one nmos transistor is off,the capacitance between gate and substrate
is co.if this transistor is on but non-saturated,what is the capacitance
between gate and source?

a.0
b.1/4*co
c.1/2*co
d.co
e.2*co
 

Re: A question about Cgs.

i think it is half Co and i think also that when it gets into saturation, it is 2/3*Co... so, most probably, you'll find it in this range...

hope i helped..
 

Re: A question about Cgs.

its 1/2 co.
if we ignore the overlap caps.
 

Re: A question about Cgs.

When NMOS is cutoff : Cgb = Co where Co = Cox * W * L
When NMOS is in triode : Cgs = 1/2 Co and Cgd = 1/2 Co
When NMOS is in saturation : Cgs = 2/3 Co and Cgd = 0.

These equations are based only on intrinsic capacitances. The overlap capacitances like Cgso and Cgdo are not considered.
 

Re: A question about Cgs.

c. 1/2co
 

Re: A question about Cgs.

1/2Co, it is generally accepted in many books. Besides i think Cgs should be capacitor between gate and source, not gate and substrate. Cgb has a constant value when the transistor is in triode or sature situation.
 

Re: A question about Cgs.

I think it is 1/2 Co
 

A question about Cgs.

I'm sure that the answer is c.
 

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