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Submitted via IRC for TheMightyBuzzard
A flip-flop is one of the most basic digital electronic circuits. It can most easily be built from just two transistors, although they can and have been built out of vacuum tubes, NAND and NOR gates, and Minecraft redstone. Conventional wisdom says you can't build a flip-flop with just one transistor, but here we are. [roelh] has built a flip-flop circuit using only one transistor and some bizarre logic that's been slowly developing over on hackaday.io.
[...] The single-transistor flip-flop works just like any other flip-flop — there are set and reset pulses, and a feedback loop to keep the whatever state the output is in alive. The key difference here is the addition of a clock signal. This clock, along with a few capacitors and a pair of diodes, give this single transistor the ability to store a single bit of information, just like any other flip-flop.
That's damned nifty.
Source: https://hackaday.com/2018/04/18/the-one-transistor-flip-flop/
(Score: 2) by RS3 on Thursday April 19 2018, @05:04PM
I'm not an IC designer, but I recall that most diodes in ICs are just 1/2 of a transistor. I forget the reasoning but basically it ends up being easier in the process.
While I'm at it, I'm not so thrilled with this circuit, but to be fair I've been doing circuits for a long time. A standard flip-flop is 2 transistors and 4 resistors. This thing is 6 resistors (one for the input is not shown!), 2 diodes, 2 capacitors, 1 transistor, and no partridge in a pear tree. And _must_ be clocked, even if you aren't doing clocked logic.
Capacitors are always a pain in an IC, and can only be very low capacitance value, on the order of a few pF. This thing would be huge on an IC scale.
There are 4-layer semiconductors which will remain in conduction once triggered on, and can be triggered off. They're not used much in logic because they're slow.
http://www.circuitstoday.com/scs-silicon-controlled-switch [circuitstoday.com]
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-7/silicon-controlled-switch-scs/ [allaboutcircuits.com]
http://www.circuitstoday.com/gcs-gate-controlled-switch [circuitstoday.com]