subthreshold region of MOSFET

Discussion in 'Analog & Mixed-Signal Design' started by Babun Pal, Jul 25, 2016.

  1. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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    Hi,

    Could anyone please explain me what sub-threshold region of operation of a MOSFET and what are the conditions to be satisfied to operate a MOSFET in sub-threshold region.

    Thank you.
     
  2. Robin66

    Member

    Jan 5, 2016
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  3. Bordodynov

    Active Member

    May 20, 2015
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    Vgs<Vth id>0
    The current varies exponentially with the gate voltage.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The sub-threshold region will cause the mosfet to heat up more than other regions of use, due to it having the most "on" resistance.
     
  5. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
    14
    1
    Hi,
    Could you please site an example fo the application of subthreshold region of operation of MOSFET.

    Thank you.
     
  6. Robin66

    Member

    Jan 5, 2016
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    From wikipedia:

    Sub-threshold electronics[edit]
    Some devices exploit sub-threshold conduction to process data without fully turning on or off. Even in standard transistors a small amount of current leaks even when they are technically switched off. Some sub-threshold devices have been able to operate with between 1 and 0.1 percent of the power of standard chips.[7]

    Such lower power operations allow some devices to function with the small amounts of power that can be scavenged without an attached power supply, such as a wearable EKG monitor that can run entirely on body heat.[7]
     
  7. benta

    Member

    Dec 7, 2015
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    An example could be a linear audio power amplifier using (complementary) MOSFETs for the output.

    Benta.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Subthreshold operation is normally used at very low currents for Class A micropower (or nanopower) circuits.
    Linear power amplifiers operate in the saturation region at much higher currents.
    The transistors in a complementary Class AB or B amplifier may rapidly go through the subthreshold region when amplifying an AC signal but that is not considered to be operating in that region.

    For that matter a MOSFET switch will also momentarily go through the subthreshold region when switching, but that's also incidental to its operation.
     
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