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CBJT NAND Gate

A project log for CBJT Logic

Complementary bipolar junction transistor logic - like CMOS, but with NPNs and PNPs

Ted YapoTed Yapo 01/09/2017 at 01:1711 Comments

Here'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.

Discussions

Yann Guidon / YGDES wrote 01/09/2017 at 01:37 point

BTW thoses are In-vs-Out curves, what about time-domain simulations ?

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Ted Yapo wrote 01/09/2017 at 01:54 point

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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esot.eric wrote 01/09/2017 at 09:07 point

I dig this comment. I wonder if there're any NAND crystal-formations that take decades :)

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Yann Guidon / YGDES wrote 01/09/2017 at 10:39 point

are you implying you're considering snail logic ? :-D

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Yann Guidon / YGDES wrote 01/09/2017 at 01:28 point

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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Ted Yapo wrote 01/09/2017 at 01:30 point

premature optimization :-P

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Yann Guidon / YGDES wrote 01/09/2017 at 01:34 point

follow the book before trying to outdo it ;-)

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Ted Yapo wrote 01/09/2017 at 01:53 point

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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Yann Guidon / YGDES wrote 01/09/2017 at 02:53 point

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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Ted Yapo wrote 01/10/2017 at 03:03 point

@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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Yann Guidon / YGDES wrote 01/10/2017 at 03:29 point

A LDO would be nice... or a diode in series ?

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