Ted YapoHere's a first try at a NAND gate. I took @Yann Guidon / YGDES's advice and went series on the bottom and parallel on top. If it works, the project is a success in some sense - every other gate can be constructed from NANDs. I've only simulated it so far.
It's a straightforward adaptation of a simple CMOS NAND. I simulated the supply at both 0.8 and 1V, and it seems to work at either one, although a little better at 1V. The base resistors limit the input currents - these should have been on the inverter inputs, too. Because of the "stacked" input stage, the inputs are not symmetrical. For instance, here's the output voltage vs the top input with the bottom input held at logical 1 (1.0V):
With the bottom input high, the NAND gate works like an inverter for the top input. And it looks like a pretty good one. The results aren't quite as good with the inputs reversed:
Here, with the top input held high, the threshold for the bottom input isn't great. Still, if you specify the Vih parameter (minimum high input voltage) as maybe 0.65V, then it should be fine.
I think this should be workable as a logic gate. I don't know about performance yet.
AND Gate
If you add another inverter stage to "clean up" the output, you get an AND gate with very nice thresholds on both inputs. Here's the circuit:
and the output with the top input high and the bottom swept (the "bad' curve above):
The output inverter produces nice thresholds for both inputs; their transfer functions are now basically identical.
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BTW thoses are In-vs-Out curves, what about time-domain simulations ?
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I haven't looked at transient response yet. But, if it takes a week to switch, it's still a NAND :-)
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I dig this comment. I wonder if there're any NAND crystal-formations that take decades :)
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are you implying you're considering snail logic ? :-D
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1) try with a resistor for each base, not shared between 2 bases
2) use that damn speedup capacitor, Luke :-D
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premature optimization :-P
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follow the book before trying to outdo it ;-)
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Yes, these are interesting ideas that might improve the performance. But you misunderstand my intent. I'm not trying to outdo it at all; I'm trying to keep it simple. Beyond "working," I don't really care about performance. I'm not going to come up with anything remotely useful with this (like all of my hobby projects); if there were something useful to be found, it would have been found already. The logic circuit in that paper died for a reason - it was inferior to other ideas at the time. Even if the extra R's and C's increased performance by order of magnitude, I'm not sure I'd add them if it means having to solder hundreds (or thousands) more connections to build something I think is interesting :-)
On the other hand, I am interested. How much do you think adding them will improve performance?
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performancewise, I think the R+C are significant because the miller effect is latent.
I am all in favor of simplicity, BTW, but the well-chosen resistors reduce power draw too :-)
I have already listed possible reasons why it was abandoned. However, circuits that work at pretty low voltages are also precious, see how they developed the first crystal watches : http://ethw.org/First-Hand:The_First_Quartz_Wrist_Watch
So maybe there is a potentially useful application, like something that works out of a single AA battery...
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@Yann Guidon / YGDES logic that runs off an AA battery is interesting. Maybe a NiMH to avoid burning it out at 1.5 with an alkaline cell :-)
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A LDO would be nice... or a diode in series ?
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