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Threshold voltage dependence on Vdb

  1. Jan 3, 2013 #1
    Why does the Vth of MOSFETs depends on Vsb and not Vdb even though MOSFETs are symmetrical devices? Is it a convention to choose Vsb over Vdb or am I missing out on something more fundamental?
     
  2. jcsd
  3. Jan 17, 2013 #2
    Because the source is usually kept at the constant. Also after pinch-off the drain is separated from channel charge by a depletion layer.
     
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