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Re: CDP1806ACE - ISA Standard committee

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  • jdrose_8_bit
    Thank you. Great explanation. I knew how bipolar transistors worked but FETs were a mystery to me.
    Message 1 of 25 , Apr 18, 2013
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      Thank you. Great explanation. I knew how bipolar transistors worked but FETs were a mystery to me.

      --- In cosmacelf@yahoogroups.com, Lee Hart <leeahart@...> wrote:

      > >
      > > What are the differences between "regular" 2N2222 transistors and Field Effect transistors when implementing logic gates?
      >
      > Quite a bit! Bipolar transistors are current-controlled; a current into
      > the base (at negligible voltage) turns them on. FETs (including MOSFETs)
      > are voltage-controlled; a voltage into the gate (at negligible current)
      > turns them on.
      >
      > You can built the same sort of circuits with either type, but the
      > details of the circuit are quite different. Compare the internal
      > schematic for a bipolar gate (7400 etc.) which is built with bipolar
      > transistors, to that of a CMOS gate (4011 etc. built with MOSFETs. (The
      > internal circuits are on the older data sheets.)
      >
      > If you wanted to build an 1802 from individual transistors, n-channel
      > and p-channel MOSFETs would work with exactly the same circuits used in
      > the 1802. The MOSFETs would cost you around 5-10 cents each.
      >
      > If you wanted to build an 1802 with bipolar transistors, you would have
      > to replace each type of gate (inverter, NAND, NOR, flip-flop, etc.) with
      > its equivalent bipolar circuit. It would wind up requiring more
      > transistors and be faster; but use more power. Bipolar transistors are
      > 3-5 cents each, but you'd need more of them so the price probably comes
      > out about the same.
      >
      > Either way, it would be a major project; like building a model Eiffel
      > tower out of toothpicks. :-)
      >
      >
      > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
      >
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