reverse biased diodes and speed of pc

Discussion in 'Homework Help' started by vvkannan, Dec 1, 2008.

  1. vvkannan

    Thread Starter Active Member

    Aug 9, 2008
    138
    11
    hello,
    I saw this question today in a book.

    'Devices with pn junctions are used to build computers .The speed of computers depends on how fast a diode can be turned off and on.Based on what you have learned about reverse bias,what can we do to speed up a computer?'

    All i know is in a reverse biased pn junction a small reverse current(which is the sum of reverse saturation current and surface leakage current) flows.
    Moreover the revese saturation current increases only with Temperature.
    But what can be done to speed up the computer?
    Thank you
     
    david mwangi likes this.
  2. Papabravo

    Expert

    Feb 24, 2006
    10,155
    1,795
    pn junctions are so last century. You should look instead to the field effect transistor, and the effects of VCC and feature size on speed versus power consumption. The story is a great deal more interesting than you might suspect.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    PN junctions when turned off they need some time (very small) to stop conducting due to internal capacitance. This capacitance is called the depletion layer capacitance. Imagine the n region and the p region as the plates of a capacitor and the depletion layer as the dielectric. This structure creates a capacitor which affects the turn off time of the pn junction. To make it turn off faster you can make the diode smaller to have less cross sectional area and thus smaller capacitance or reduce the doping levels as to increase the width of the depletion layer and thus reduce this capacitance.
     
  4. vvkannan

    Thread Starter Active Member

    Aug 9, 2008
    138
    11
    Thank you very much
     
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