what are the applications of depletion type and enhancement type MOSFET?

Discussion in 'Analog & Mixed-Signal Design' started by Babun Pal, Jul 19, 2016.

  1. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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    Hi,

    I've gone through the material on Depletion type MOSFET and Enhancement type MOSFET. I have few douts:

    1). What are the applications of depletion type MOSFET e.g. Can it be used as a trans-conductance amplifier?
    2) What are the applications of enhancement type MOSFET e.g. Can it be used as a switch?


    Would you be kind to clarify these doubts.

    Thank you.
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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  3. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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  4. Papabravo

    Expert

    Feb 24, 2006
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    The easiest way to think about them is that a depletion mode device will be ON with no bias voltage between gate and source. You have to bias the gate negative with respect to the source to turn it off. An enhancement device is OFF with no bias voltage between the gate and the source, and you have to apply a positive bias to the gate to turn it on. Both kinds of devices can be used as switches, amplifiers, oscillators and such.
     
  5. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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    Thank you
     
  6. BobTPH

    Active Member

    Jun 5, 2013
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    And depletion mode MOSFETs are rarely used. I suspect that they only exist because that is the JFETs operated.

    Bob
     
  7. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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    Hi Bob,

    Thanks for your reply.
    Could you please site an example where depletion type MOSFET is used?

    Thank you.
     
    HW-nut likes this.
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Information is readily available on the internet. Here's an appnote and another.

    I didn't notice them mentioning that depletion mode MOSFETs can have current increased above the zero bias current by applying an appropriate gate voltage; positive for NMOS depletion mode. They are rarely used. I have never used a discrete depletion mode device and the ones used in IC design were only for decoupling caps.
     
  9. Babun Pal

    Thread Starter New Member

    Jul 13, 2016
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    Thank you.
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    A depletion JFET is very similar to a thermionic triode with scaled down voltages. If you know how to auto-bias a triode - you've got the procedure for a depletion JFET.

    The enhancement MOSFET is easier to use as a switch - just operate the gate at either above or below VGSthr. It can be run in linear mode with plenty of nfb to stabilise the operating point.

    Most VHF/UHF FETs are depletion MOSFETS and a few specialty manufacturers do power depletion MOSFETs.
     
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