A question about MOS transistor that in linear reigon

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wjxcom

Joined: 07 Sep 2005
Posts: 399

19 Jun 2006 4:15 A question about MOS transistor that in linear reigon

Hi, all: I have a question about MOS transistor that in linear reigon. As we know, when a MOS transistor is in saturation reigon, we can use the model shown in the attachment, but when a MOS transistor is in linear reigon, can we use the model that shown in the attachment? or may be there has another model for MOS transistor that in linear reigon?

thanx!!!

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jluhzw

Joined: 15 Nov 2004
Posts: 131
Helped: 15
Location: Hangzhou China

19 Jun 2006 4:54 Re: A question about MOS transistor that in linear reigon

I think it could not use the model used in the saturation.

safwatonline

Joined: 19 Nov 2005
Posts: 1418
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Location: EGYPT

19 Jun 2006 6:57 A question about MOS transistor that in linear reigon

transistor in linear is a resistor

wjxcom

Joined: 07 Sep 2005
Posts: 399

19 Jun 2006 7:39 Re: A question about MOS transistor that in linear reigon

Dear, safwatonline: look at the attchment please, this is a cmfb circuit. In this circuit, M4 and M6 are in linear reigon.

If we look M4 and M6 as resistors, how to deal with the port VON and VOP? I think that if VON and VOP opetare on the resistors, they can not genetate any result which has relation with the port CMFB.

The circuit can be found in this:http://www.edaboard.com/ftopic176000.html. i.e. cmfb.jpg

thanx!!!

lavitaebelle

Joined: 26 Jan 2006
Posts: 75
Helped: 11

19 Jun 2006 14:39 Re: A question about MOS transistor that in linear reigon

you can definitely use the model for MOS in linear or saturation. The definition of gm( δid/δvgs) and ro(δid/δvds) too still remain the same. Only thing is that the values are different as the current to voltage relation is linear when compared to square law in saturation.

boooser

Joined: 16 Jun 2006
Posts: 18

20 Jun 2006 4:48 Re: A question about MOS transistor that in linear reigon

wjxcom wrote:

If you use that model, I think you should add something.
For in linear region.
The gm will have be uCox(W/L)Vds, more like a linear resistor.

ipsc

Joined: 08 Jun 2006
Posts: 75
Helped: 1

24 Jun 2006 19:37 Re: A question about MOS transistor that in linear reigon

boooser wrote:

If you use that model, I think you should add something.
For in linear region.
The gm will have be uCox(W/L)Vds, more like a linear resistor.

gm= uCox(W/L)Vds =>linear resistor, how? For the time being if we ignore 'r0' then

Id= gm*vgs={uCox(W/L)Vds} * vgs. Here vgs is small signal Vgs and Vds is large signal.

That means 'gm' is non linear unlike the saturation case.

greenhand

Joined: 28 Jun 2006
Posts: 11

28 Jun 2006 8:57 Re: A question about MOS transistor that in linear reigon

When mos works in triode region , it can be looked as a v-controlled resistor

williamy

Joined: 26 May 2006
Posts: 66
Helped: 1

29 Jun 2006 1:47 A question about MOS transistor that in linear reigon

if vds is very small, then the mos is in deep linear, in this region, the MOS can be thought a resistor; if vds is big but smaller than vds(sat), then, the MOS work in non-saturation, in this region, MOS is still a voltage-controlled-current-source, just the gm is not same as the gm in saturation region

zyyang

Joined: 19 Jan 2006
Posts: 57
Helped: 2
Location: P.R. CHINA

29 Jun 2006 3:08 Re: A question about MOS transistor that in linear reigon

sure i think so ,when the mos is in linear region, the gm will be u*c*w/l*(vgs-vth)vds-0.5vds^2,it also can be view a gm , only small than the gm in saturation , but it isn't a voltage controlled resistor because it didn't work in deep linear region