Re: CDP1806ACE - ISA Standard committee
- Thank you. Great explanation. I knew how bipolar transistors worked but FETs were a mystery to me.
--- In firstname.lastname@example.org, 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