Passive Optical Diode Created At Purdue University

wbr1 writes "Researchers at Purdue University have managed to create a silicon device that acts as a passive diode for infrared optical signals. From the Purdue news release: 'The diode is capable of "nonreciprocal transmission," meaning it transmits signals in only one direction, making it capable of information processing, said Minghao Qi (pronounced Chee), an associate professor of electrical and computer engineering at Purdue University. "This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing," said Qi.' One of the same researchers had already (using similar technology) created a way to convert laser pulses to RF."

Comments

Is there a better article on this somewhere?

[KClaisse]

Both the summary and TFA are devoid of anything concrete on how this is actually done. It basically says what the title does, they created a diode. Telling me that light entering the opposite side doesn't make it through really doesn't tell me anything the word "diode" in the title doesn't. I'm sure the science behind this particular device is both clever and interesting but you'd never be able to tell since that information is completely missing. Reporting on stories is nice, but shouldn't journalists actually strive to make their articles contain actual information on what they are covering? You'd think a story about a new discovery would actually contain information about how it actually works (since that's the actual "new" part anyway).

Re:Is there a better article on this somewhere?

[KClaisse]

Both the summary and TFA are devoid of anything concrete on how this is actually done. It basically says what the title does, they created a diode. Telling me that light entering the opposite side doesn't make it through really doesn't tell me anything the word "diode" in the title doesn't. I'm sure the science behind this particular device is both clever and interesting but you'd never be able to tell since that information is completely missing. Reporting on stories is nice, but shouldn't journalists actually strive to make their articles contain actual information on what they are covering? You'd think a story about a new discovery would actually contain information about how it actually works (since that's the actual "new" part anyway).

Completely missed the second link to the university's release. Still not a very informative article however.

Re:Is there a better article on this somewhere?

[gl4ss]

what hz are the radio transmissions done at? because the article.. well.. the article justifies that it can transfer more data simply because it's optical at one point before transmission.

Re:Is there a better article on this somewhere?

[sempir]

Having read the summary and TFA and understood what they were saying backs up your comments re paucity of information. IE if I can understand it there must be more! Actually.

Re:Is there a better article on this somewhere?

[Victor Liu]

Here is the link to the actual article in Science: http://www.sciencemag.org/content/early/2011/12/21/science.1214383

Re:Is there a better article on this somewhere?

[denpun]

Subscription required....

Re:Is there a better article on this somewhere?

[kubernet3s]

That would be Science for you. This is a scientific paper, not an AmSci survey piece. TFA was a piece of science journalism, so they probably haven't had time to fully compress the actual paper

Re:Is there a better article on this somewhere?

[TapeCutter]

Here's what they did, I don't understand a word of it but it was simple enough to google.

Holy Entropy

[physburn]

It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon. Now convert it a transistor, and with a maxwell daemon, (Quantum Weak Measurement, + Quantum Computer, + Classical Prediction Logic) and we have (possibly) a free entropy device, capable of turning waste (heat) energy back to useful energy.

---

Third Magic @ Blogspot

Re:Holy Entropy

[Penguinshit]

Entropy is always free. The Universe has been doing it without charge for billions of years.

Re:Holy Entropy

[XiaoMing]

It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon.
Now convert it a transistor, and with a maxwell daemon, (Quantum Weak Measurement, + Quantum Computer, + Classical Prediction Logic)
and we have (possibly) a free entropy device, capable of turning waste (heat) energy back to useful energy.

From TFA:

Depending on which ring the light enters first, it will either pass in the forward direction or be dissipated backward, which creates one-way transmission.

It seems to more just act as a nonlinear lens, dissipating (or more likely scattering) preferentially in the backwards direction.

Re:Holy Entropy

[Black Parrot]

It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon.

Are you thinking that infrared mirrors are not possible? Does the article claim that his device does work without increasing entropy?

Re:Holy Entropy

[kubernet3s]

Infrared light is not heat. I don't know where people got this idea. It is light. When it is absorbed, it may cause certain molecules to gain heat energy, but it is still light. This is a device which absorbs or scatters when you shine light on one side of it, and transmits when you shine light on the other side of it. I assume when heat energy is generated within the device, it diffuses isotropically from the point of matter-light interaction throughout the material until a definite temperature is reached, as thermodynamics predicts. If you believe that materials with different absorption cross sections at different spatial orientations allow you to violate the second law of thermodynamics, then you hardly need to construct something so elaborate: a board painted two different colors on either side should suffice. Lasers themselves, whose cavities emit a lot more in one direction than in the other (and which generate a good deal of heat in their lasing medium in a largely homogeneous fashion, but let's not get bogged down in reality) should constitute a huge violation. You should let everyone in the physics community know, as this seems like a fairly large oversight in our model of reality /sarcasm

If you're going to go around with a name like physburn, please ensure you understand what you're talking about

Re:Holy Entropy

[CODiNE]

Infrared light is not heat. I don't know where people got this idea. It is light. When it is absorbed, it may cause certain molecules to gain heat energy, but it is still light.

I think it comes from a basic lack of understanding of how heat is given off by fires. If all you know is something about photons and light... and that light absorption causes heat, you fill in the blanks and reason out that fire must release most of it's energy in the non-visible light spectrum. Also infrared cameras show hot and cold, therefore many may reason that infrared = heat.

In my memory of high school physics we didn't go in depth into heat transfer nor radiation. If that was the standard curriculum of the time then many people of gen X could believe that heat transfer is due to infrared light. It's interesting that the wikipedia page on Heat shows that many science textbooks use the term in confusing ways. Also

They found the predominant use among physicists to be as if it were a substance.

So one could be a competent scientist and still use the term in a semantically incorrect way, unknowlingly passing on disinformation.

It would be interesting to do a little informal polling of what heat is and how it transfers. What percentage of people know how it really works? What percentage of scientists?

Re:Holy Entropy

[newcastlejon]

This device is pretty big to make a transistor.

So was this but look how that turned out.

Re:Holy Entropy

[kubernet3s]

Heat was actually believed to be a substance, until the middle of the 19th century.

True, it is a fairly subtle concept. I am much more concerned about the lay confusion between temperature and heat than between light and heat. However, it should be fairly well reinforced that light does not interact with something unless it interacts: windows heat up less than asphalt in the presence of energetic radiation in the optical regime.

Re:Holy Entropy

[rubycodez]

Heat was actually believed to be a substance, until the middle of the 19th century. Not by everyone, Francis Bacon , Robert Boyle , and Robert Hooke didn't believe that in the 16th century, and Benjamin Thompson (Lord Rumford) proved it wasn't in the late 18th century.

Re:Holy Entropy

[kubernet3s]

Dammit, I keep misremembering my science history. If only there was some kind of large database of this kind of information that I could interface with remotely

Does not "open the door"...

[gweihir]

Why do so many researchers lie so shamelessly to the press? This may be a step in that direction, but it is a rather small one. Key components are missing and a lot depends on the actual characteristics of this device.

Re:Does not "open the door"...

[Melkman]

And even if major components like a light transistor are developed I don't see optical computing taking off in the foreseeable future. This "diode" is kind of weak since it stops reverse light by dissipating the energy. So any non trivial computing function made with it will consume a non trivial amount of energy in the form of input light. Compare this to electronics where a switch in the on or off state doesn't use energy apart from leakage. The major thing consuming energy there is switching states, and even that is only caused by the components being non perfect, living in an non perfect world as we do.

Namely

[robi5]

Finally, we got the Pixel Qi

Re:R&D at American Univesities

[Black Parrot]

Every time I read about an R&D achievement at an American university, the lead (and often associate) researchers are Chinese nationals.
Do Americans no longer conduct advanced R&D at American universities?
Seems foolishly short-sighted, if so.

Nothing like a Qi spell to give technology a boost...

And maybe he is an American, or is working on his citizenship. This country used to take pride in being a melting pot.

Great news for the slashdot smart people

[AbRASiON]

Bad news for us who have no idea what this means or implies. What could this do if this thing were real? I haven't seen a laymen explanation.
We're not all smart guys you know.

Re:Great news for the slashdot smart people

[kubernet3s]

http://simple.wikipedia.org/wiki/Diode
http://simple.wikipedia.org/wiki/Logic_gate

All those degrees in looking things up online finally paid off. You're welcome, citizen!

Re:Great news for the slashdot smart people

[Anonymous Coward]

A transistor acts as an electrical switch. Basically, it means that when an input is provided, the rest of the circuit can do something, but at the same time the input is electrically isolated from the rest of the circuit.

Before transistors, there were relays and tubes which accomplished the same thing. They were slower, larger, hotter, and used a lot more electricity. And they were prone to burning out. As a result, computers were hopelessly complicated, the size of small rooms, and were programmed with a screwdriver. And "bugs" in the computer program were sometimes, literally, bugs. A moth, in at least one story. And an IBM chairman famously stated that he saw a world-wide market for about 5 computers.

Then the digital transistor came along and revolutionized that. They were smaller, faster, and required much less power. And they were cheaper, too. The integrated circuit - millions of transistors etched onto a single silicon die - revolutionized that further.

A transistor also acts like a diode, in that it only lets current flow in one direction. But note that this isn't really even necessary: relays, for instance, didn't prevent current from flowing backward. The main thing is that the input is electrically isolated from the output, not that it allows current to flow in only one direction.

So basically, they have everything required to build an optical transistor, except for the switching part. Which is kind of the more important part anyway.

Re:Great news for the slashdot smart people

[kubernet3s]

Seeing as the positive aspects (applications, reasons why this is a good thing, even the basics of the theory of photonics) are included in the first five sentences of TFA (which I will refrain from pasting here, out of respect), I'm not sure how my post could be assigned even that bare step above. If you are looking for a laypersons description of the optics theory behind the device design, I can assure you by it's very nature, such an explanation does not exist. If you are looking for a more metaphysical explanation of why faster computers are a truly POSITIVE thing (computer's degrade social fabric, you know) then I'm afraid I can't help you, but can tell you this is probably not the right venue to look for those answers.

Re:Great news for the slashdot smart people

[moogied]

So assuming that they could build the pre-requisite components this would be a part in a purely 'optical' computer. Basically right now data goes through a basic flow like this: Computer generates data. Computer transfers data to network card. Network card converts electrons into 'light' and 'beams' it across the fiber optic cable to its destination. At its destination it is reconverted into electrons from 'light' and that destination does whatever. That conversion from electrons to light takes time. Albeit a super small amount of time, it takes time. I don't know the actual amount of time, but lets say its a millasecond for ease of understanding. This has an impact on the latency of a signal because data is not transmitted from A to B. It is A to B to C to D to E to F, etc etc. 20 or 30 hops. That's an extra 20-30 millaseconds of latency purely because it has to convert it from 'light' back to electrons and back. Over and over. We do not currently have technology that would allow data manipulation to occur purely through light. Everything has to go back to electrons. This passive optical diode is a small piece of a much larger set of technologies we would require to make data routing over fiber optics to become a pure 'light' based system. Another way to think of it is that we need to create most of a modern silicon based computers pieces with light operating devices. At least on a circuit base level. The end goal would be a system would nothing ever has to be converted, and thus a massive reduction in latency. Analogy: We have an alien language that we need to convert to english. We cannot convert it directly to english for whatever reason. Instead we convert it to spanish THEN into english. This new invention would be a step towards alien to english conversion without that middle step. It makes crap faster :P

Re:Great news for the slashdot smart people

[50000BTU_barbecue]

"As a result, computers were hopelessly complicated,"

That doesn't follow. Computers were hopelessly simple back then. Or are you claiming the latest quad core CPU with a billion transistors is simple compared to a relay adder?

Re:Great news for the slashdot smart people

[LoRdTAW]

To be fair, you can build logic gates using diodes. The only drawback is that the devices operate on the principal of voltage drops across diodes and level shifting, bad for complex circuits.

Re:Great news for the slashdot smart people

[tibit]

It does not operate on the principle of voltage drops, it's like saying that cars operate on the principle of heating up their environment (65%+ of your gasoline heats up the air around you). Diode logic operates, obviously enough, utilizing the large ratio of forward-to-backward current flow across an isolated semiconductor junction. Voltage polarity across a diode turns it on/off, but what is turned on is the current flow. I don't know where the idea about level shifting came from, it's not necessary at all for diode logic.

Re:Great news for the slashdot smart people

[LateArthurDent]

I'll give you the answer that I think you're looking for, but I will rant a bit at the bottom about what I believe is a flaw in your attitude. If the rant is something you will ignore because you're not interested in constructive criticism, feel free to not bother reading anything after the explanation.

The goal is to build circuits that are not electronic, but optical in nature. This could result in faster computers (if we can make fast enough optical switches), but it will almost certainly result in more efficient computers, as losses due to heat can be minimized. In an electronic circuit, you have conduction losses, switching losses, etc. An optical circuit would produce heat as part of light production, and wherever light is absorbed. Presumably, those losses would be lower than in an electronic circuit.

How does this development move us in the direction of optical computing? Well:

A logic gate is something that gives an output based on the inputs given and a certain rule. For example, and "and" gate will output "true" if all of its inputs are "true", and will instead output "false" if any of its inputs are "false". Every single thing implemented in binary computers are a combination of logic gates, and in fact you don't even need different types of gates, since every boolean logic expression can be simplified to a combination of certain types of gates, such as the NAND gate. In the world of electronic components "true" and "false" are sometimes referred to as "high" and "low" because we consider voltages above a given threshold as true, and below a threshold as false.

An important part of implementing logic gates is that the electrical signal doesn't flow the wrong way. For example, you don't want whatever is connected to the output to influence what the input is. A diode is just that. It allows flow in one direction, but not another.

Diode behavior is just part what we want though. What we really want are controlled switches, which are what transistors are. You want to allow light through a path only if a light is shined upon the "gate". Using those, you can build the logic gates discussed above.

Now for the rant:

This is barely one step above the pretentious douchery of a LMGTFY link. If you can't be fucked writing a simple explanation of why it's a positive thing then don't bother.

You're missing the point of the LMGTFY link and not learning the lesson it is supposed to impart with a bit of humor. You're probably missing the lesson because you're too busy being offended by it. Don't be, it's light humor.

It's not that we think you're not smart enough. It's that it's really confusing that you could have typed up "diode" on google and arrived at a page that explains what diodes are in less time than it took you to make a post asking somebody to explain to you what diodes and logic gates are. In addition, you wouldn't have to wait for somebody to reply, or filter the messages of people like the guy above and mine. So you're not actually being lazy or doing less work, you're just not using your time efficiently, and LMGTFY and wikipedia links are our way of telling you how you can go about becoming more self-sufficient.

Now, depending on your background, the wikipedia page may offer you no help at all, so it's perfectly ok to come here after you've done that bit of work, and ask for clarification on a specific point. I wrote a lot of stuff up there, some of it you may know, some of it you may not. I may be far off base on what it is that you actually wanted to know. If you had said, "I don't understand how diodes are useful in creating logic gates", then I'd just have included the bit about not wanting the output to affect the input, and how what you really want is not a diode per se, but a controlled switch. If you instead had said, "I don't understand how logic gates can be used in computing", then nothing I wrote above is really useful, and I should have really given you a little bit more on boolean logic and digital circuits.

Bull. They're halfway, the easy half at that.

[_0xd0ad]

The "most fundamental part" of logic isn't one-way transmission, it's the ability to control that transmission by applying a voltage to the transistor's gate. The fact that current will only flow one direction between the emitter and the collector is really not that important by comparison.

You can't build logic from diodes.

Re:Bull. They're halfway, the easy half at that.

[kubernet3s]

Yes, but controlling how much light goes through a device is...um...super easy. Like caveman easy.

Actually, I'm not an expert on photonics, the analogue of voltage could be wavelength, in which case upconversion can provide the same function. There's a lot of fluff on the Purdue site but this is actually a fairly interesting device and the research isn't bad.

Re:Bull. They're halfway, the easy half at that.

[sgunhouse]

Not voltage, signal. Maybe there's a way for the signal to be light (creating an all-light computer) or maybe it's a voltage - or maybe it is something else. But it has to be something we can control.

Re:Bull. They're halfway, the easy half at that.

[_0xd0ad]

My point was that the signal is the important part. They have no way of switching this optical diode.

The diode effect is fairly irrelevant and unimportant. As a matter of fact, digital logic doesn't require something to act like diode at all: relay logic doesn't use diodes.

Re:Bull. They're halfway, the easy half at that.

[Electricity Likes Me]

Actually it's really really hard. The optical transistor is the current holy grail of photonics and optical computing. The person who invents it will be incontinently rich.

Re:Bull. They're halfway, the easy half at that.

[moogied]

Realistically the person who invents it will get a nobel prize, write a book or two, and thats it. The company he works for that paid the hundreds of millions(probably billions) of dollars for his equipment and personnel will become richER.

Re:Bull. They're halfway, the easy half at that.

[_0xd0ad]

Your point being, I take it, that you can create certain gates with diodes (AND and OR).

There are some truth tables which can be achieved by nothing but AND and OR. There are some that cannot. All truth tables can be achieved by solely the use of either NAND or NOR, but you can't create those gates using just diodes.

Digital logic requires the ability to do something on the 0 state. Without an inverting gate, you can't do that, and diodes can't invert.

Re:Bull. They're halfway, the easy half at that.

[_0xd0ad]

You can't build logic for any given truth table using nothing but diodes. You can only build logic for some truth tables, which doesn't give you programmable digital logic. Happy now?

Re:Bull. They're halfway, the easy half at that.

[tibit]

You can't build logic from diodes.

You most definitely can, even complex logic like multipliers:

A static multiplier, capable of simultaneously multiplying two 4-bit binary numbers, was designed and built to demonstrate the practicability of current-operated diode logic gates. Approximately 270 diodes were required to construct the twenty gates used in the static multiplier. Dynamic tests of the assembled system indicated a reliable capability of 333,000 multiplications per second.

Just google for some ideas. You can even build voltage-controlled multiplexers using nothing but diodes -- quite good ones, even. Your basic high-frequency sampler (going up to tens of GHz) is nothing but a sampling capacitor in a sampling diode bridge. Such bridges maintain symmetry that preserves integrity of the sampled differential signal and are the simplest way to quite accurately sample a quickly changing signal. They have incredible bandwidth given their simplicity.

Re:Bull. They're halfway, the easy half at that.

[tibit]

An optically controlled switch is easy. Any medium where you get optical saturation lets you implement a light-controlled switch. You can also have media that, say, change opacity when exposed to light of one wavelength, so you can control transmission of say red light using UV. You can also have a light-controlled-gain device, like, say, a light-pumped laser -- turn off the pumping light and gain drops below 1. Turn on pumping light and you have positive gain. The power levels involved are not very practical, and the lower power devices can be slow, but you can definitely achieve light-controlled amplification of light -- an optical transistor. You can also easily achieve voltage-controlled amplification using a semiconductor laser. It's the lack of practical implementations that slows things down, that's all -- as far as I understand it.

Re:Bull. They're halfway, the easy half at that.

[tibit]

I think you're wrong. You can build logic for any given truth table, using only "plain old" diodes, nothing exotic. This was state of the art in late 50s/early 60s. I'm pretty sure you could do programmable logic as long as you'd use an active device like an SCR to retain the state of the programmable "fuse". LUTs and multiplexers, the staples of modern programmable logic, are fairly easy to do with nothing but diodes. And they aren't terribly slow either, you could probably build a current-driven 10 LUT "PLD" that would operate at more than 1MHz, using nothing but Schottky diodes.

Re:Bull. They're halfway, the easy half at that.

[_0xd0ad]

That's a pretty interesting concept, but it uses an entirely different binary representation (current polarity switch for 0/1, rather than voltage potential). In essence, it means that every signal is 2 leads rather than 1, and switching them creates a NOT gate.

You might be right, but I'd want to see a working flip-flop before I'd accept that diodes could be used for digital logic.

Re:Bull. They're halfway, the easy half at that.

[_0xd0ad]

Oh, and I should mention... optical signals only have 1 lead (fiber), not 2. My brain is too tired to try to figure out what that would mean as far as trying to use optical diodes to accomplish anything similar to the current-direction-based logic used for that multiplier.

Re:Bull. They're halfway, the easy half at that.

[tibit]

The paper shows that the current representation is merely a faster dual of the voltage representation. The circuits be mechanically transformed from one form to another. Current-driven diodes do work as flip-flops, but this logic of course needs external active components to inject input currents and to propagate currents between combinatorial stages. That's how you get flip-flops or any other function that requires feedback: you put a current mirror between output and the input.

If you want purely diode-based logic with no other kinds of active components, then you need tunnel diodes. Look up Esaki Diode Logic Circuits by Neff, Butler and Critchlow (again, from the 60s). You can also implement this logic using modern two-terminal devices such as diacs (or their transistor-based implementation).

Re:Bull. They're halfway, the easy half at that.

[tibit]

With two fibers you can encode information in phase difference, and I bet that would "polarize" a two-input optical diode OK.

Re:Bull. They're halfway, the easy half at that.

[kubernet3s]

but isn't half that challenge the construction of a diode? Once you have the diode, it's as simple as fluorescence, no? At least, in princple.

Re:Bull. They're halfway, the easy half at that.

[rubycodez]

nope, you can build two logic functions non-inverting logical AND and OR. The state of the art in the 1950s was to use transistors, sometimes coupled with diodes as DTL (diode transistor logic). Once you have amplification (which comes with the ability to invert if you so desire), things get easy and you can do any logical function.

Re:Bull. They're halfway, the easy half at that.

[tibit]

Mr Henry Reinecke seems to disagree. I've downloaded the paper and they do use current drivers and current mirrors to drive inputs and couple stages (including feedback from outputs to inputs), but the logic itself is all diodes. I've done a quick simulation of the most complex network he used in the multiplier, and with modern diodes and well laid out board you could probably run it at 10MHz. In the paper he shows that diode logic has dual representation -- one uses voltages as signals, another uses currents as signals. The voltage signal based logic is simply slower because various capacitances play a big role, but you can have exactly same logic done for voltage signals or current signals.

Do note that I think his logic could be running with an AC carrier (yep), and you could use transformers to couple stages, and it'd work without any passive devices for moderately sized networks. I'm thinking of prototyping such a thing just to show that his multiplier, even if impractical, can be done completely using diodes and passive devices.

Re:Bull. They're halfway, the easy half at that.

[rubycodez]

very interesting, but of course he is using active devices, if you can pull it off all passive without voltage drops killing the works best of luck

Re:Bull. They're halfway, the easy half at that.

[tibit]

It's not the voltage drops that kill it, it's voltage levels and the fact that a current source needs to have infinite impedance. It's hard to approximate that without active devices.

Re:Bull. They're halfway, the easy half at that.

[tibit]

I meant obviously without any active devices, if one considers a linear transformer to be a passive device (as opposed to a magnetic amplifier that would be considered active).

Optical CPU's ?

[Latinhypercube]

Forget this minor improvement of losing optical to digital i/o's. Doesn't this mean optical Cpu's ? Which I'm sure would be magnitudes faster (cooler?).

Re:We keep knocking...

[Electricity Likes Me]

We're on the threshold of a lot of things, for a long time, before they become reality.

Newton wasn't a lone genius (parallel development notwithstanding) he was just the right man at the right time, standing on the shoulders of the right giants.

I suspect, once ITER is complete, or maybe it's successor, and practical fusion power becomes reality, then we'll just as equally forget that "we were on the threshold" for over 50 years.

Re:Logic using diodes

[_0xd0ad]

You can build some logic using diodes.

Not all logical functions can be implemented in diode logic alone; only the non-inverting logical AND and logical OR functions can be realized by diode gates.

You can build some logic using a plain old switch, too: IF the switch is closed, THEN light the bulb. Not terribly useful. Neither is diode logic.

So....

[trum4n]

It's the most expensive 1 way mirror, ever.

Correct me if I'm wrong but...

[g0bshiTe]

'The diode is capable of "nonreciprocal transmission,"

I thought any diode only allowed transmission one way.

Re:Correct me if I'm wrong but...

[sidthegeek]

I'm pretty sure that's what "nonreciprocal" means.

Re:Correct me if I'm wrong but...

[g0bshiTe]

My point is they make it sound like they created the very first one.

Re:Nonlinearity

[tibit]

The paper is out online only.

Re:Relay logic DOES use diodes :-)

[tibit]

Those diodes perform an auxiliary function and are not doing any sort of logic by themselves (as they would were it diode, not relay, logic). If you're careful about it, you can do without diodes, using a snubber instead. Heck, there are applications where you don't want a diode across a coil at all -- that's when you want to control broadband emissions. A snubber-on-coil circuit is tuned and has high damping, you can tune it to have relatively low frequency oscillations. With a diode you have fast switching action, high dV/dt and lots of nasty, broadband emissions.

Re:Logic using diodes

[tibit]

Here's an abstract for ya. And this is nothing new: it's from work done in late 50s:

The realization of switching functions using current-operated diode logic gates, which employ the direction of current as the binary variable, is presented. Two realization methods are discussed. The dual method consists of a set of rules which are analogous to the procedures employed for the realization of voltage-operated circuits. The lattice method is based on the transmission characteristics of a lattice network of four series-connected diodes. Either method is capable of realizing any arbitrary transmission function, although the number of diodes required may be different. Hybrid networks, which combine the advantages of both methods, are described to illustrate the versatility of current-operated techniques. Practical design procedures are included to guide the designer in the application of the realization rules. A static multiplier, capable of simultaneously multiplying two 4-bit binary numbers, was designed and built to demonstrate the practicability of current-operated diode logic gates. Approximately 270 diodes were required to construct the twenty gates used in the static multiplier. Dynamic tests of the assembled system indicated a reliable capability of 333,000 multiplications per second.

If you can make a 300kHz 4x4 multiplier using diodes, then I'd say this is hardly some logic -- in my book, at least. The wikipedia article on diode logic, and most other intro-level articles I could find, really miss on how diode logic was (and is) used, and provide only some lame, almost useless examples.

Re:back is getting tight

[datavirtue]

how is this modded down?