Linear, Active, ohmic, saturated region

Discussion in 'General Electronics Chat' started by aamirali, Feb 16, 2012.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
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    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
     
    Last edited: Feb 16, 2012
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I think you meant to say saturated instead of ohmic in the second sentence. Please clarify and re-post.
     
  3. aamirali

    Thread Starter Member

    Feb 2, 2012
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    yes its saturated.
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
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    Yes, I believe that's correct.

    No. It's ohmic. Saturated in MOS means something different than it does in BJT.
     
  5. aamirali

    Thread Starter Member

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

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

    Thread Starter Member

    Feb 2, 2012
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    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
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
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    Not sure what you're saying here, so I can't comment at this time.

    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.

    It seems that 9 out of 10 people I talk to gets confused.
     
  9. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Me too I get confused by the way you write.
     
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