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Homework Help: Mosfet design doubt

  1. Mar 27, 2014 #1
    Can someone explain this sentence in MOSFET design..

    The Since the drain will be at a positive voltage relative to the source the two pn junctions can be effectively cut off simply connecting the substrate terminal to source terminal.
  2. jcsd
  3. Mar 27, 2014 #2
    As far as I know the substrate and source are usually connected, and does not cut off the transistor in any way.
  4. Mar 27, 2014 #3


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    Gold Member

    Is it NMOS or PMOS?
  5. Mar 28, 2014 #4

    rude man

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    Homework Helper
    Gold Member

    Since the drain is stated to be more + than the source, the device is an NMOS unless the device is operated in the inverse mode, which is almost never the case.

    As stated in a previous post, the souce & substrate are usually but not always connected. That connection does not cut off the device.
  6. Mar 30, 2014 #5


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    Staff: Mentor

    ... with the substrate connected to the source, the two back-to-back pn junctions cause the drain-source path to be a non-conducting path. Under these conditions (with the absence of gate voltage) the enhancement-mode MOSFET is in cut-off.
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