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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: 0) by Anonymous Coward on Thursday April 19 2018, @08:48PM
How will we make connections for many billions of corresponding external capacitors, when copper pillar pitch is dozens of μm?
Or shall we include these lolhuge capacitors on-die, just to make it bigger and more expensive than using more tiny transistors?
He uses two 1500pF caps for clocks down to 200kHz. Scaling that to a minimum clock of 1GHz, that's "only" 0.3pF.
I did a little research to double-check my intuition on this; I found data relating the 65nm process node first, so that's what I went with.
At 2 fF/μm2, which is optimistic, each capacitor is 12μm by 12μm. Considering a 6T SRAM cell being well below 1μm2, that's easily enough for dozens of flip-flops.
I won't say it can't have some useful application somewhere, but cramming billions of flipflops in a chip definitely isn't it.