CMOS inverter

Discussion in 'General Electronics Chat' started by tuoyo22, Nov 9, 2007.

  1. tuoyo22

    Thread Starter New Member

    Nov 9, 2007
    3
    0
    Hi everybody just want to know this for my Cadence design

    In a CMOS inverter why do we assume that the load Capacitance is INDEPENDENT of Voltage, if we want to calculate for the fall or rise time.

    Any Idea will be appreciated
    Thanks
    T
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    For all capacitors, the formula is: T = RC. The charge time is not dependent on voltage.
     
  3. tuoyo22

    Thread Starter New Member

    Nov 9, 2007
    3
    0
    Thank you!
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Actually, the typical load for a CMOS gate is more CMOS gates, plus some wiring capacitance. The input capacitance to a CMOS gate is somewhat dependent on voltage, but the calculation would be an absolute nightmare, so assuming that the load is independent of voltage is a good idea. ;)
    Simulation takes the voltage dependence into account and does the calculation for you, and is therefore somewhat more accurate.
     
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