An observation about the types of logic that can be etched into silicon.

One of the questions which I had blogged about before, was that, of whether the MOSFET transistor-type inherently has 3 pins or 4. This question has a practical aspect, which I did not mention in that posting, but which is eventually interesting.

When the very high-end Electrical Engineers design chips – ICs – and specifically, when they designed earlier-generation CMOS circuitry, they were not only limited by what the fundamental properties of a MOSFET were, but also, by how many layers the machines at the time could deposit onto the chip, each of which needed to be etched and treated in a separate, very precise stage of the manufacturing process. This is why I find it helpful that the WiKiPedia article I just linked to, displays a CMOS circuit, and how it was originally implemented, as their explanation of the subject.

What the reader may take note of, is the example of the P-channel MOSFET, which consists of a Source, a Drain, a Gate, a Bulk Electrode, and a Substrate. The role of this Bulk Electrode needs to be given some special attention. Because of the way these transistors were in fact etched, additional, unintentional, “parasitical” transistors could form, for example, a ‘hidden’ PNP, Bipolar Transistor, between the Drain, the N-doped well, and the P-doped substrate. In theory, if the N-doped well became negative enough, with respect to either the potential of the substrate or that of the P-doped Drain, then this parasitical transistor could become forward-biased, and start to conduct and amplify its own currents, with the Drain acting as Emitter, with the N-doped well acting as Base, and with the Substrate acting as Collector. The same thing could theoretically also happen, with the P-doped Source acting as Emitter instead.

The way this behaviour was prevented, was by connecting the N-doped well to the positive supply voltage, and always keeping the P-doped substrate connected to the negative supply voltage. This formed a so-called ‘isolation diode’, and prevented the parasitical transistor from becoming active.

Well in the circuit which I had clicked together using the NG-SPICE software, each MOSFET was a 4-pin component, and my main point of attention was on how to get my software to acknowledge whatever circuits I had entered. If the circuit in question needed to be etched, using the original technology, then the bulk electrode of each MOSFET would also need to be connected either to the negative supply voltage in the case of an N-channel MOSFET, or to the positive supply voltage in the case of a P-channel MOSFET. Hence, the existence of 3-pin MOSFETs was not due to whether the transistor-type was inherently so, but just due, to how certain forms of the technology were being manufactured, as consisting of a minimal number of layers. And this also forced the inclusion of the transistors as having 3 electrodes into certain schematics, just because their implementors could not implement the 4-electrode variety in certain cases – and in fact, often.

If the schematic was ever to be etched into silicon, as I drew it in my earlier posting, and as NG-SPICE was simulating it, then at the very least, a much-more recent form of Integrated Circuit would need to be used as architecture. And then one problem which would next follow would be, that this more-recent architecture also makes the transistors much smaller, such as 40 Nanometre or 10 Nanometre technology (?), which would result in individual transistors that cannot handle the amounts of current which discrete circuits require, so that the complications of driving output pins would become more pronounced.

One reason for which I did not elaborate this fact in my past posting was the realization that I’d have to link to yet-another WiKi-page in order to do so, and that WiKiPedia articles get edited from time to time. I did not know that the WiKi would keep the traditional layout of the CMOS layers a part of their article for so long.

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Getting the Orca Screen-Reader to work under Plasma 5

In case some readers might not know, even though computing is heavily visual, certain advanced desktop-managers can be set up for impaired people to use – which also falls under the category of “Accessibility”. This includes the ability of the computer to speak a robotic description of what’s happening on the screen, in case a user can hear, but not see properly.

There are some users who feel they should stick with Windows, because Accessibility can be so hard to set up under Linux.

There are other users who are sorry they every clicked on “Accessibility”, because now they cannot turn it off.

If a visually-impaired user wants Accessibility set up on a Linux computer, I’d definitely suggest letting a trusted other person set it up, because until it’s set up, complicated things may need to be done, and accessibility will not be set up, so that the end-user will not benefit from Accessibility, while trying to set it up.

Some regular users find screen-readers trying for their patience, because of the fast, robotic voice, until they manage to shut it down again. Personally, I only find screen-readers trying, If I happen to have set one up late at night, because the voice could cause some sort of noise-complaint from my neighbors, droning on until I manage to disable it again. In the middle of the day, I don’t find these experiments trying.

I guess that a good question which some people might ask me, would be why I even do such an experiment, given that I’m not visually impaired and don’t need it. And what I do is set everything up until it works, and then disable it again.

On my recently-installed Debian / Stretch computer named ‘Plato’, which is also running Plasma 5 as its desktop-manager, I just did manage to get this feature to work, and then to disable it again.

(Updated 15h50, 1/17/2018 : )

The first thing I had to do, was install a long list of packages. The list below includes what was installed, but it should not really be necessary to give the command to the package-manager manually, to install everything here, because some of these packages will follow as dependencies from other packages. But here is a roundabout list:

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