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What is the difference between the triode ( ohmic ) region and the saturation ( linear ) region in mosfet ?? It's confusing since both regions are linear but why does mosfet work as an amplifier in saturation not in triode ? Isn't triode equal to the active linear region in Bjt ? If it is not then what is the triode region and what is it used for ??

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  • \$\begingroup\$ It doesn’t stop being an “amplifier” it simply becomes extremely lousy as a linear amplifier. Triode is where it becomes more useful as a switch or a variable resistor. \$\endgroup\$ Commented Dec 7, 2018 at 12:30

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The MOSFET triode region: -

enter image description here

Is equivalent to the BJT saturation region: -

enter image description here

The BJT active region is equivalent to the MOSFET saturation region.

For both devices, normal amplifier operation is the right hand side of each graph. In switching applications, both devices are "on" in the left hand half of the graph.

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  • \$\begingroup\$ @ Andy Does a clean bit of math describe the bipolar SAT region, like the inverse parabolic describe that FET TRIODE region for long-channel FETs? \$\endgroup\$ Commented Dec 7, 2018 at 13:06
  • \$\begingroup\$ @analogsystemsrf dunno, never looked into it but it sounds like the basis for a good question if you want my opinion. \$\endgroup\$
    – Andy aka
    Commented Dec 7, 2018 at 14:01
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    \$\begingroup\$ An example of naming-tyranny: For an oldfart like me, "triode" region implies the vacuum tube linear operating region, while "saturation" implies an anode dragged down to a low voltage. D'oh. Semiconductor physics is the root of these terms for MOSfets, apparently history is not. \$\endgroup\$
    – glen_geek
    Commented Dec 7, 2018 at 14:55
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    \$\begingroup\$ The number of peeps that refer to the MOSFET triode region as the saturation region is certainly not zero and I've argued with one particular person on these boards but he refuses to accept. That's yet another concern @glen_geek !! \$\endgroup\$
    – Andy aka
    Commented Dec 7, 2018 at 15:08
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    \$\begingroup\$ There are no free meals in life but the price here isn't too high!! \$\endgroup\$
    – Andy aka
    Commented Dec 11, 2018 at 10:05

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