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what is "MOSFET bidirectional analogue gate"?

Discussion in 'Electronic Basics' started by nick, Apr 3, 2005.

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  1. nick

    nick Guest

    thanks!
     
  2. nick

    nick Guest

    and what is it used to?
     

  3. I presume you are talking about products like the 74VHC4066 for instance.
    Datasheet here:

    http://www.fairchildsemi.com/ds/74/74VHC4066.pdf

    These devices are quite similar electrically to mechanical switches in many
    ways. They can pass current in either direction, and they do not
    significantly interfere with analog voltages. A regular CMOS digital gate
    will normally convert any analog voltage not right at the switching
    threshold and produce logic level outputs.

    The same basic functionality can be obtained but with superior (for some
    purposes) specifications using things like two discrete MOSFETs wired back
    to back and their gates bias properly. A practical implementation could be
    made by connection the gates together of each device. Both sources would
    also be connect together. The drain pins would function as bidirectional
    input and output. Somehow you have to drive both gates, and one of the
    easiest and more versatile ways would be with a photovoltaic optical
    isolator. These devices differ from regular transistor output optical
    isolators in that they contain solar cells which actually output a small
    amount of useable power.
     
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