Linear, Active, ohmic, saturated region

aamirali

Joined Feb 2, 2012
412
1. What is linear region in transistor or mosfet. Is it ohmic region where voltage & current have linear relation or is it saturated region.

2. Active region?

3. in mosfets, in ohmic mode Vgs > vth and Vds < (vgs-vth).
in ohmic mode Vgs > vth and Vds > (vgs-vth).

When I apply 10V at Vgs with Vth=2V & Vdd=20V. Now I have noted Vds < 0.5V or it is typically drop across Rdson.
According to above equation device since Vds< vgs-vth. It says its ohmic region but I thick device is saturated

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Ron H

Joined Apr 14, 2005
7,063
3. in mosfets, in ohmic mode Vgs > vth and Vds < (vgs-vth).
in ohmic mode Vgs > vth and Vds > (vgs-vth).
I think you meant to say saturated instead of ohmic in the second sentence. Please clarify and re-post.

aamirali

Joined Feb 2, 2012
412
yes its saturated.

Brownout

Joined Jan 10, 2012
2,390
1. What is linear region in transistor or mosfet. Is it ohmic region where voltage & current have linear relation or is it saturated region.
Yes, I believe that's correct.

When I apply 10V at Vgs with Vth=2V & Vdd=20V. Now I have noted Vds < 0.5V or it is typically drop across Rdson.
According to above equation device since Vds< vgs-vth. It says its ohmic region but I thick device is saturated
No. It's ohmic. Saturated in MOS means something different than it does in BJT.

aamirali

Joined Feb 2, 2012
412
So that means if I apply high & low on gate of mosfet, it goes into ohmic & cut off state instead of saturated & cut off

Brownout

Joined Jan 10, 2012
2,390
It goes from cutoff to saturation to ohmic. In MOSFET, saturation is the 'active' region. Don't get this confused with BJT regions.

aamirali

Joined Feb 2, 2012
412
Hi,
Can you give more exact details where I can read it.

I think saturated means maximum current no more current at particular condition. &
ohmic or linear means where losses are depends on Vds & Ids. if mosfet goes into ohmic then losses will be huge.

Yes u r right I am geeting confused b/w two

Brownout

Joined Jan 10, 2012
2,390
I think saturated means maximum current no more current at particular condition.
Not sure what you're saying here, so I can't comment at this time.

ohmic or linear means where losses are depends on Vds & Ids.
Ohmic or linear is the region where ID is a function of vGS and VDS. Id rises ( very ) roughly linearly with VDS, hence the name 'linear'. Saturation is the region of constant ID, determines by VGS-VT. In the saturation region, ID isn't much affected by VDS.

Yes u r right I am geeting confused b/w two
It seems that 9 out of 10 people I talk to gets confused.

atferrari

Joined Jan 6, 2004
4,752
Hi,
Yes u r right I am geeting confused b/w two
Me too I get confused by the way you write.