# Second try at USSR integrated circuit analysis

In the previous post, I logicked my way into the geometry of a transistor. But in fact, the geometry turned out to be wrong since none of the circuitry made any sense. So I decided to start from this diagram, which is similar to the 74141 diagram. Which makes sense since the К155ИД1 is the same as the 74141.

From the 74141 datasheet.

So if I look at the A input, I should see an inverter and a second inverter. The outputs from these go to output transistors.

Next, I drew one of the transistors in the above circuits as a generic three-terminal device: 0 for a terminal with no region around it, 1 for one region, and 2 for two regions.

Then, I drew the inverter circuits based on what I saw on the chip.

Then I logicked my way to a reasonable schematic. The two-terminal question-marked component seems to be maybe a resistor. 0 seems to be the base, 1 is the emitter, and 2 is the collector.

OK, this makes some sense. The two transistors on the left are an inverter. X taps off the output of the inverter, and the third transistor on the right is what you'd typically see in a 7400-series input. It's just two diodes back to back in a current-steering circuit. Since it taps off the emitter of the output, it is the inverse of X.

That means that we have this interpretation of a transistor:

Now, let's take a look at the outputs.

OK, that's not right according to the datasheet. But on the other hand, it could work. If A is high, and if DCB = 100, then we want 9 to sink current and 8 to be off. If A is high then X is low, which means that as long as the base is active, 9 will sink current.

I still haven't identified the protective zener diodes on the outputs.

So if the terminal designations are correct, then it's possible that this is the doping schema.

So what I've been calling the "hillock" in the middle of the rectangular region is perhaps the p-doped base. Again, this is weird compared to what you usually see, which is the collector completely surrounding the base.

The collector probably has an n+ region, which improves connectivity. It is embedded in an n or n- region forming the collector.

Note that I think the base contact seems to overlap into the rectangular region. If the rectangular region is n-doped and somehow connects to the collector, which is perhaps an n- region, then this may form a Schottky diode, meaning that these transistors are Schottky transistors.

So technically the collector does surround the base, it's just that it does it through a differently doped region.

Again, I don't have enough knowledge of IC fabrication to know whether this would work. But it seems... logicky?