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The Vacuum Transistor: A Device Made of Nothing

spectrum.ieee.org

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Re: The Vacuum Transistor: A Device Made of Nothing

#41

Post by cfallin »

marcosdumay wrote: post #32
ars wrote: post #25

Earlier quoted context omitted.

You started by saying 5x voltage, switched to 5x power, and ended with 5x energy. Those are not the same thing. You can have 5x voltage without changing the power or the energy.

You can have 5x the voltage without changing the power consumption if you reduce the capacitance. If you keep the transistors at the same size, a computer working with 5x mode voltage will use 5x more power if operating at the same frequency. (But you can probably make it run faster...) That said, except for very few embedded applications, computers today operate on a voltage that's much bigger than the silicon band…

Actually, all else being constant, 5x voltage yields 25x power:

P = CV^2 * f (multiply by activity factor if pedantic; assuming all transistors toggle every cycle here.)

Re: The Vacuum Transistor: A Device Made of Nothing

#42

Post by neltnerb »

mikepurvis wrote: post #8
ChuckMcM wrote: post #7

Oh that is pretty cool. I wonder if they have considered them as power switching devices. Something like that which had an effective Rds of nano-ohms could make electric cars more efficient.

Yeah, I'm skeptical about plans to build whole integrated circuits out of them, but these high frequency, low-loss devices could be killer for a lot power electronics applications— motor controllers, DCDCs, etc.

Not sure about high power, but the physical requirement for small size scale combined with the engineering goal of high current is usually contradictory.

I do absolutely think this could be awesome for lower power ultra tiny DC-DC converters though. For instance:

http://hexus.net/tech/news/psu/64161-finsix-laptop-power-sup...

is pushing to high enough frequencies so as to not need an inductor at all. Problem with high frequencies is that usually the efficiency drops, so there's a tradeoff. But if you can avoid the switching losses by moving to a transistor with higher operating frequencies, it might be quite good =)

Or the tiny size might work well for letting you do cool stuff like on-chip DC-DC conversion where you don't need an inductor because it's all so fast...

Re: The Vacuum Transistor: A Device Made of Nothing

#43

Post by mbenjaminsmith »

marcosdumay wrote: post #33
zwieback wrote: post #11

Would a guitar amp built with these sound like a tube amp?

I'd bet computers will be emulating the sound of vacuum tubes way before any of those things get into market. You can get the correct vacuum tube-like amplification from a computer today, it's just that tubes are still cheaper. A/D converters and first stage linear amplifiers are only getting cheaper (even at this, post Moore's law era), thus it's only a matter of time before computers retire valves on yet another ap…

> You can get the correct vacuum tube-like amplification from a computer today, it's just that tubes are still cheaper.

It is absolutely not the case that tube amplifiers are still sold because they're cheaper than solid state amplifiers + DSP. Their sounds is preferred and they are much, much more expensive to produce.

The valves (which don't enjoy the economies of scale they once did) are only part of the cost. The power supply of a tube amp is usually more complex than a solid state amp and they generally need output transformers because of high output impedance -- transformers that are linear through the audible band are expensive to produce.

At scale you could easily build a SOTA DSP card suitable for emulating "tube sound" for less than the cost of a single channel output transformer. Line 6, among others, have built businesses based on that fact.

Re: The Vacuum Transistor: A Device Made of Nothing

#44

Post by pjc50 »

daveslash wrote: post #19
pimlottc wrote: post #12

Regarding the opening anecdote - some have suggested the Soviets used vacuum tubes so that their planes would survive the electromagnetic pulse from a nuclear explosion.

DISCLAIMER: This is what I remember once hearing in an ECE class. I was hesitant to post this comment given that it might be garbage, but perhaps someone can help confirm or disprove this. I once heard that one of the reasons the Soviets continued to use analog systems was that they were "faster, more compact, and more power efficient" [than a digital computer]. This came at the cost of flexibility. For example, an o…

At 1980s levels of integration, then I'd agree that for many sorts of signal processing it's easier to do it in analog than digital. Especially if all your engineers are trained for analog. In 2014 the situation is the other way round.

Robustness of power electronics is another consideration: tubes are mechanically fragile but not vulnerable to ESD, whereas FETs are, especially during assembly. If their factory process control was poor it would have been easier to stick with the tubes.

Re: The Vacuum Transistor: A Device Made of Nothing

#46

Post by valarauca1 »

kken wrote: post #40
valarauca1 wrote: post #9

Earlier quoted context omitted.

The problem is with carbon in general is it has a band gap 5x larger then Silicon. Which overall (but not entirely) means if you want to build a transistor with Diamond (or graphene) you need to put 5x as much voltage into it. The reason graphene is great for transistors is with its higher band energy its 5x harder for it to soft set itself. So if we pretend todays 11nm transistors have a 1% chance of electron tunnel…

>The problem is with carbon in general is it has a band gap The band gap is not a function of the element alone, but mainly of the crystal structure. Different allotropes of carbon have vastly different band structures. Diamond has a high band gap, as you mentioned. But Graphene has none, and that is one of the major obstacles of the material.

The problem with having none is that makes your transistors even more vulnerable to quantum effects.

Re: The Vacuum Transistor: A Device Made of Nothing

#47

Post by bwanab »

pimlottc wrote: post #12

Regarding the opening anecdote - some have suggested the Soviets used vacuum tubes so that their planes would survive the electromagnetic pulse from a nuclear explosion.

They mentioned it at the end of the article which was disappointing since I'm sure many readers didn't get that far.

Re: The Vacuum Transistor: A Device Made of Nothing

#48

Post by DigitalJack »

danparsonson wrote: post #45

How does one speed-test a device that switches significantly faster than the available electronics?

drive a periodic waveform and sample repeatedly. Assuming you don't somehow sample the same point in the periodic waveform each time, you'll eventually get the complete waveform.

Re: The Vacuum Transistor: A Device Made of Nothing

#49

Post by tesseract »

marcosdumay wrote: post #32
ars wrote: post #25

Earlier quoted context omitted.

You started by saying 5x voltage, switched to 5x power, and ended with 5x energy. Those are not the same thing. You can have 5x voltage without changing the power or the energy.

You can have 5x the voltage without changing the power consumption if you reduce the capacitance. If you keep the transistors at the same size, a computer working with 5x mode voltage will use 5x more power if operating at the same frequency. (But you can probably make it run faster...) That said, except for very few embedded applications, computers today operate on a voltage that's much bigger than the silicon band…

The silicon band gap is ~1.1V at room temperature. Mainstream modern processor core voltages are around 1.2V (maybe less for the very latest parts) and "ultra low voltage" processors operate as low as 0.7V.

Re: The Vacuum Transistor: A Device Made of Nothing

#50

Post by jpmattia »

DigitalJack wrote: post #48
danparsonson wrote: post #45

How does one speed-test a device that switches significantly faster than the available electronics?

drive a periodic waveform and sample repeatedly. Assuming you don't somehow sample the same point in the periodic waveform each time, you'll eventually get the complete waveform.

> Assuming you don't somehow sample the same point in the periodic waveform each time, you'll eventually get the complete waveform.

To add an example of a real technique: You can use a short laser pulse and change the time-of-flight (mirrored path on a stepper motor, for instance). This technique will get you to the terahertz region, which is pretty much state of the art for where electronic devices still have gain.

http://en.wikipedia.org/wiki/Terahertz_time-domain_spectrosc...

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