Low-Voltage, Complementary Bipolar Logic

A project log for YGREC-Si

Yet Another Discrete Computer with Silicon transistors

Yann Guidon / YGDES 01/10/2017 at 07:296 Comments

@Ted Yapo suggested a very unusual circuit in @esot.eric's thread

Soon enough, he tried the circuit and created #CBJT Logic !

I found out that Baker (of diode clamp fame) had explored this kind of circuit:

And tonight, Ted tried some of the enhancements, which reduced the consumption and increased the speed !Speeding Up the NOT Gate

The sweet spot seems to be between 1V and 1.1V with approximately 10ns of propagation time per inverter, and a not-too-high current draw...

I am very tempted to play with this kind of gates for this project but experience with the other technologies show that a critical gate is the MUX2 (and MUX4) which are not trivial to design with this method. I should investigate "pass gates" made of NPN and PNP transistors...


Ted Yapo wrote 01/10/2017 at 19:11 point

MUX2 is (3) 2-input NANDs and an inverter - 14 transistors.

MUX4 is (9) 2-input NANDs and 2 inverters - 40 transistors.

Use small transistors :-)

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Yann Guidon / YGDES wrote 01/10/2017 at 19:33 point

There MUST be a better way...

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Ted Yapo wrote 01/10/2017 at 20:29 point

Open collectors?

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Yann Guidon / YGDES wrote 01/10/2017 at 20:39 point

In my designs, I can factor the many MUX into a common decoder and many sums-of-products (OR of ANDs). So the required MUX8 is basically many AND2 followed by a OR8 (or OR9 maybe for the immediate argument).

AND2 is quite easy, you designed one (still to be tested).

OR8 is another beast, because one "leg" is just 8 transistors in parallel, while the other is 8 transistors in series !

OR8/9 can be built with a tree of OR3 which is a reasonable compromise... But the more compact gate would be NOR3. Fortunately, NAND3 is equally easy to design...

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Ted Yapo wrote 01/11/2017 at 13:38 point

You can't do more than 2-input gates at 1.1V supply voltage.  No way to have all those series transistors work - even with two in series, the upper one has a funny threshold.

NOR is just as easy to design as NAND, but again, only with 2-inputs.

At least so far.

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Yann Guidon / YGDES wrote 01/11/2017 at 21:50 point

I don't want to sound "elitist" but 2-input gates don't cut it enough for me :-D NOR3 or die ? hmmm....

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