Recent Pole-Zero Pairs
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▨ The semiconductor industry in Bulgaria Vol. 2
▨ Small-signal and large-signal MOSFET channel resistance
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▨ Dominant gate capacitance of a MOSFET
▨ Mr. Sievert, a fictional character
▨ "This could be a very strong paper"
▨ Major milestone: Oxford thesis submission
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How many words do you know ending on tron?
Make yourself a cup of "coffeetron" warmed-up by the magnetron driven by the kenotron in your microwave oven powered and protected by cathodotron in your local power plant. Make yourself comfortable then search for any of these terms and have some fun:
synchrotron; magnetron; thyratron; klystron; klystron; kenotron; electron; neutron; iotatron; cyclotron; cosmotron; dynatron; betatron; audion; pliotron; mesotron; ignitron; strobotron; negatron; antineutron; tevatron; calutron; bevatron; positron...
The etymology of -tron endings come from Ancient Greek, where they have been used as a suffix denoting an instrument. How about the electron? Well, my digestion here is that it is an instrument in the end. Also note how many particle accelerator construction attempts mankind has made. The rest of the majority happens to be electronic tubes, cool! Let me know of your suggestions for expansion of the list? Happy physicsing!
some random thoughts on engineering ethics
Ever had the feeling that all technologies surrounding us are an offspring of the hidden powers of organized crime groups?
In the early 1940s, with the number of great discoveries in 19th century ignited by the second technological revolution a new era was born - the digital revolution. Back in 1947 in his short story "Little Lost Robot", Issac Asimov predicted that technology would have advanced sufficiently by century's end that it would allow for humanity to establish a base on asteroid to perform research on space travel. With the landing of Rosetta last year, Asimov's story as usual held true again. The past 100 years have shown that the engineering disciplines, compared to all other fields of science, have probably by far the highest impact on society. The last is especially true with the emergence of the information age, which gives us one of the most influential instruments for psychological control humanity has ever had. With all that said, engineering science plays an important role in the development of our society, and to a large extent the future of mankind now lies in the hands of engineers.
Now teleporting back to early 1900 in the era of the second industrial revolution. With growing demands for easeing of mankind life by means of industrializaton, engineering established itself as a distinct profession. With the erection of a number of large civil engineering constructions, there had been a series of significant structural failures, including some spectacular bridge engineering disasters. Notably the Tacoma Narrows Bridge collapse and the Ludendorff Bridge disaster. These had a profound effect on engineers and forced the profession to establish some technical and construction practices which were driven beyond anything else but the price of human lives. As a measure, the development of ethical standards was established by an impressive number of world organizations, placing life safety to highest order. I am tempted to quote the engineer's seven canons here, published in the Code of ethics, established by the American Society of Civil Engineers in 1914.
It is here to mention that engineering science constantly faces a number practical trade-offs, which also means that material savings and cost-efficiency are an immense feature of standard consumer engineering. When engineering ethics face the model of modern corporate powers, often, highly exothermic reactions can occur and as is often seen in nature the physically strongest monkeys always win banana fights. Unfortunately strongest does not always mean wisest, in fact, the contrary is usually the case. It means that engineering practice until now needed not only to take care of life safety, but also the corporate wallet. A wallet which vigorously dislikes any kind of drainages. In retrospect, the early established engineering ethics have so far worked quite well in most cases, despite that they are not always obeyed by large enterprises, take the recent case with Volkswagen for example.
Nevertheless, the consequences of such historical disasters may seem like a piece of cake, compared to what disasters of the future information age could be if appropriate measures are not taken. Not surprisingly history tells us that mankind may again fall into the same traps, some of which have been identified as early as 600 BC with the sudden collapse of the Egyptian civilization. The most drastic and rapid social change that mankind has ever experienced actually took place some three thousand years ago! A change from primitive barbarism to a posh civilization (in the context of such a far distant era) till a complete disaster and a vanish of identity. This is all just history, however, process recurrence is something normal in nature, at least to the extent of trusting empirical laws such as Zipf's. This historical de-brief should hint that nowadays engineering science is facing new challenges, unconditionally different from any other kind of past experiences.
During the 80s, coining the term cyber warfare in his novel "Neuromancer", William Gibson successfully pinpointed the soft threats of the information age - data and identity thefts and document forgery. But this was just the beginning, as the power of the Fourth World has reached influential levels in society beyond anything else seen in the past. With all of that said, due to this rate of influence, technology control should be tightened to a whole new order of magnitude - control which now widely lies in the hands of engineering ethics. Although technology provides us with rich possibilities it does not mean we should employ all in all, just because we can. Spying nowadays is a matter of a bit flip - it is needless to say that builders should not always be putting the donkey where the master says. Instead, it is the engineer's responsibility to act professionally and in line with the principles of sustainable development, no matter what the boss says. If each of us acts with merit of honor following certain principles - the collapse of the Fourth World would never happen. If misuse can be prevented in lowest layers of hierarchy, then it'd better be the scientists and engineers; hence some amendments in our code of ethics is needed, in fact we have been in need for it for a long time. Now, I realise that such argument is going to run into immediate objections: "who are you to say what code of ethics is". And on one level, this may obviously be true. However, during my short life experience I have seen a number of engineering ethics misconceptions which are inciting me to think that something is wrong. Another less visible principle delusion which also needs addressing is the modern model of self-induced slavery; what do I mean by that? Example - medical electronics is a field of engineering with a primary aim of making people's lives better, however, nowadays I see the majority of it as monstrous money making machine. How can brain chip implants, pacemakers or disposable endoscopic cameras be sold with nearly a thousand percent (if not even much more) profit margins? Products, the majority of which were developed using public money to start with; and are primarily used in the public sector. All of the above makes what's available today practically inaccessible, or if accessible not without some form of arm-twisting. This is the second, much less obvious threat of our digital revolution requiring more emphasis in the philosophy of science. We should not fall into this trap - getting down, surrendering and rendering what we have discovered into the rulership of some large enterprises represented by single identities.
Having control over mankind's way of thinking, sensing and experiencing information has been by far the most powerful tool scientists have ever held. Such tools combined with the caprice of some corporate maggots can form an explosive substance for humanity. Engineers - always endeavour personal commitment in what you do, amplify your moral principles to highest order and never fall into someone else's plans!
Wiener processes and the integration of white noise during the voltage slewing process of a current integrated into a capacitor are something which I have been playing around for some time now. Here is one example showing us why hand calculations using wide sense stationary noise source assumptions are not always accurate. The AC noise analysis is a good methodology for noise contributor estimation, however, in some cases it gives us a fake noise picture and this is where transient noise analysis comes handy. Here I just want to show an example of how white noise accumulates during a capacitor charge in the time-domain. Imagine a noisy current source discharging an initially charged capacitor to a certain value:
The ideal switch charging the cap is controlled via a pulsed source, while the current mirror is constantly sinking current at a fixed rate. If we run multiple transient noise runs of the above schematic we may discover that the actual ramp slew rate looks more smething like this:
The latter process comes from the fact that the power spectral density (PSD) of the noisy transistor is uniform in both left and right of the zero axes and that the voltage fluctuations accumulate in time. This process in statistics in known as a Wiener or Random walk process. It is a well studied phenomenon which is also widely used in stock market analysis and prediction. The difference here is that it is applied as a noise integration on a capacitor.
The main characteristics of interest in our case, for a generalized Wiener process are the variance and standard deviation with time. As the used PSD is uniform, the generalized Wiener process has:
mean value of zero: $z(t) - z(0) = 0$
variance of: $z(t) - z(0) = t$
and standard deviation of: $z(t) - z(0) = \sqrt{t}$
It is exactly the standard deviation that is of most interest for us. It implies that the longer we ramp, the quadratically the standard deviation increases, eventually reaching infinity. To verify this experimentally, I made a test case using external components.
When we deal with exteranl components it is often hard to measure noise levels in the order of microvolts due to a number of interference factors. Instead, I decided to use an integration capacitor of 22uF and large artificially induced noise current. The latter was injected by controlling a switched current source using a white noise source. Here is the whole setup:
After a day of experiments with the sampling rate, mean currents, external interference debug etc. I finally managed to capture the effect and I've made a combined gif animation. Here is is:
The animated gif file shows 15 measurements with mean integration current swept from 60 to 200uA and a static additive white noise of 2uA (ramp of first frame has no added noise). I used a rather large integration capacitor (22u) and this is the reason why I had to boost the added current noise level to such a high value. Also note that the ramp time is about 300ms. The screenshots show a cumulative x8 curves plotted on top. There might be some additional aliasing artifacts due to the low sample rate (scope runs out of memory for higher sampling rates at this huge period of 300ms) however, I did some measurements with an analog scope and by looking at the phosphor memory I could confirm that the random walk is indeed random and chaotic.
The ramp non-linearity at the high voltage end is caused by the PNP BJTs I used for capacitor reset and the switchable current source. There are some second order effects in this test, however, I think it kind-of gives an informal representation of the process. Stay tuned for more during the next couple of weeks.
This work took a while, so I thought that it deserves a few words in the blogs. During the past year or so, I have been working on an image sensor ADC testchip. It was finally taped out yesterday! What's left now is some additional gastronomical work on the tapeout cake and the drainage of a rusty bottle of champagne.
The core of the testchip is a fast 12-bit column-parallel ramp ADC at 5u pitch, utilizing some special counting schemes to achieve the desired 1us ramp time at slow clock rates. Alongside, to be able to fully verify the pipelined CDS functionality and crosstalk, I've built a pixel array in line-scan configuration, some fast LVDS drivers, clock receivers, references, state machines, a few 8-bit iDACs, bond pads, ESD, and some other array-related stuff, all from scratch! The chip has a horizontal resolution of 1024 and 128 lines with RGBW filters and microlenses.
On the top-left corner there are some experimental silicon photomultipliers and SPAD diodes. These I plan to measure for fun and I promise to post the results in any of the two blogs.
Unfortunately, this chip wouldn't yield tons of publicaiton work, apart from the core ADC architecture and comparator. To test the ADC one needs a whole bunch of other fast readout blocks, which in the end are not something novel, but yet, one needs them and designing these take time. Finishing up this test system was a lot of work and I realize that it might be a bit risky and ambitious to be doing this as part of a doctorate. What if it fails to work because a state machine had an inverted signal somewhere? Or the home-made ESD and pads suffer from latch-up? Or the LVDS driver CMFB is unstable and I cannot readout data out? Or there is a current spike erasing the content of the SRAM? Or, or, or ?
We university people don't have the corporate power to tapeout metal fixes twice a month until we're there. I probably have another two or three chip runs for my whole doctorate. It may therefore be better (and more fun) to stick with small but esoteric modules, which one can verify separately and have time to analyze in detail. But hey, I'll quote a colleague here: "It is what it is, let's think how we can improve things."
Let's wish good luck with the production and see what we end up with.
