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Can Transistors Be Made To Work When They're Off?

timothy posted more than 4 years ago | from the off-on-what's-the-difference dept.

Power 89

An anonymous reader writes "Engineers at the Belgian research institute IMEC are looking at the use of silicon transistors in the sub-threshold region of their operation as a way of pursuing ultra-low power goals. A chip the engineers are designing for biomedical applications could have blocks designed to operate at 0.2 or 0.3 volts, researchers said, according to EE Times. The threshold voltage is the point at which the transistor nominally switches off. Operating a transistor when it is 'off' would make use of the leakage conduction that is normally seen as wasted energy, according to the article."

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Average, Anonymous Coward (0)

Anonymous Coward | more than 4 years ago | (#32559860)

Cool! So... what does that mean?

Re:Average, Anonymous Coward (3, Insightful)

Ethanol-fueled (1125189) | more than 4 years ago | (#32559916)

To use a car analogy -- it's like driving the car at idle speed without actually hitting the gas pedal.

It's most noticeable if you drive a big truck with an automatic transmission -- just shift it into "D" and coast along at .2 miles per hour. You could also do it with a manual transmission, but you'd need very fine control of your clutch-foot.

Re:Average, Anonymous Coward (2, Informative)

corsec67 (627446) | more than 4 years ago | (#32560094)

Driving with my foot off the gas works really well on I-70 East towards Denver, you can stay at 70MPH for a while there. Or in flat terrain, coasting along at 700rpm in second gear sometimes works well.

Which made me think about this, and is really probably where this research would have effects: transistors on the edge of a high-potential region, so that even if the transistors are "off", there is more flowing through them than others in the middle of an "off" block.

Re:Average, Anonymous Coward (1)

Bakkster (1529253) | more than 4 years ago | (#32564114)

Which made me think about this, and is really probably where this research would have effects: transistors on the edge of a high-potential region, so that even if the transistors are "off", there is more flowing through them than others in the middle of an "off" block.

Right, to further expand on the car analogy, it's like driving the car with only idle and 10% throtle.

Except for some quantum transistors, they are never completely 'off'. Usually 'off' current is several orders of magnitude less than 'on' current, but it's still present. Put another way, the two regions are low resistance and high resistance. The goal is to use the difference between 'high resistance' and 'really high resistance' for 0 and 1 logic.

The added benefit is that this would operate at low voltages. Even if resistance stayed constant, power is proportional to the square of voltage. Again, if resistance stays constant and voltage halves, the power will be 1/4.

Re:Average, Anonymous Coward (1)

compro01 (777531) | more than 4 years ago | (#32560386)

Even more noticeable on a car with a high idle. My old 1981 Chevy Caprice classic would get up to about 15mph at idle, which was about 1500rpm.

Re:Average, Anonymous Coward (1)

biryokumaru (822262) | more than 4 years ago | (#32561128)

I had the point distributer on my old 69 'vette so screwed up I had to open up the choke to about 30 mph at idle just to keep the damn thing from dying. If I could get it started, that is.

With it that wide, my wife wasn't actually strong enough to brake the car reliably. I don't know why, it always seemed to break reliably when I was driving it =].

Re:Average, Anonymous Coward (1)

operagost (62405) | more than 4 years ago | (#32565078)

1500 RPM? I don't think the engine in my current car spins that fast at highway speed in overdrive! You must have had some serious stalling problem to keep your idle that high.

Re:Average, Anonymous Coward (1)

compro01 (777531) | more than 4 years ago | (#32565524)

Yes, the car was a piece of junk. The list of correctly functioning components was shorter than the list of broken/malfunctioning ones when I stopped driving it 5 years ago.

Re:Average, Anonymous Coward (0)

Anonymous Coward | more than 4 years ago | (#32562428)

but you'd need very fine control of your clutch-foot.

Once the car is moving and you've 1st gear engaged, it's nearly impossible for the engine to stop. Don't hit the clutch and the car just keeps moving, as it would with an automatic transmission.

Re:Average, Anonymous Coward (1)

spazdor (902907) | more than 4 years ago | (#32587998)

My doctor says that I have clutch-foot, you insensitive clod!

Yes and No (2, Interesting)

ModernGeek (601932) | more than 4 years ago | (#32559874)

I believe that if you were to try and utilize the leakage current, it would only cause that much more resistance, making it require more current to stay "off". This would be a good way to get a government grant in publishing some R&D for this, but in reality, I imagine that the amount of complexity that this would add to a device would outweigh any benefits. Plus, most transistors that just sit there in the off state are off because the entire device is off and doesn't require any current. The energy put into thinking about this would far outweigh any perceived benefits.

Re:Yes and No (5, Insightful)

NevarMore (248971) | more than 4 years ago | (#32559938)

The energy put into thinking about this would far outweigh any perceived benefits.

Indeed. All scientific research is utterly useless and wasted time unless it has immediate and forseeable tangible benefits.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32559996)

Pretty much. Why do you think it took WWII to move things along?

Re:Yes and No (0)

ModernGeek (601932) | more than 4 years ago | (#32560006)

No matter which way you spin this, it's a waste of energy. A moderate car trip to hold a meeting about this would take up more energy than this "research" would save if it ended in replacing every transistor that sits in the off position drawing what a single AA battery could power for over a year. This proposed research has the potential to get so much grant money for doing what every Electrical Engineer already works towards in current designs. This is nothing more than putting green spin on a problem that doesn't even really exist. The money should be put into Research and Development, but this is just snake oil.

Re:Yes and No (1)

kdogg73 (771674) | more than 4 years ago | (#32560056)

I think this could be considered a paradox. Until we reach the goal, this research shall use energy to preserve energy. This application can apply to many things.

Re:Yes and No (0)

ModernGeek (601932) | more than 4 years ago | (#32560072)

There is no paradox, at this point, we should focus on putting money toward Nuclear Energy, Fusion Power (yes, there is progress in this field), Hydro Electric, and getting rid of our gasoline-diesel based transport infrastructure. I don't think it's a bad thing if someone wants to design better transistors, but I do think that it should be done on their own dime. My argument is that public funds flock to this sort of thing, and it needs to be avoided.

Re:Yes and No (3, Insightful)

Anonymous Coward | more than 4 years ago | (#32560230)

Sheesh - RTFA already.

Low power devices have their uses - the article even mentions one, a body-powered medical device. They aren't trying to reduce overall energy consumption.

BTW, nice inclusion of a political dig in there as well - you must be lot of fun at parties.

Re:Yes and No (1)

Idiomatick (976696) | more than 4 years ago | (#32561644)

You pay Belgian taxes? Not that that would matter. IMEC is an independent research facility so no taxes were paid. Perhaps one of their forsight-less idiot partners paid for it ... like Samsung or Intel.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32562092)

that's not completely true
it's a spinoff of the KUL (catholic university leuven) and it does receive
subsidies from the KUL and thus from the belgian taxpayer (about 40 million/year last i read -> although one could interpret that as contract-work)

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32570298)

Yes, IMEC is an independent research facility, but it receives a substantial amount of taxpayer money. Speaking just from my own experience I can say I have worked with IMEC on a number of projects and currently have three active ones. All but one of the projects received significant funding either from the Belgian government (more specifically, the Flemish government) or the EU. Given its close ties to Katholieke Universiteit Leuven it should hardly be a surprise that a lot of its funding comes the traditional university route....

Re:Yes and No (1)

Frank T. Lofaro Jr. (142215) | more than 4 years ago | (#32567384)

The only Fusion Power that works is the razor.

Fusion still uses more energy that it provides.

It isn't a matter of not being economical (which can change, e.g. if power prices go up), but of being a net energy sink.

Except of course for the hydrogen bomb.

Too bad we can't harvest the energy off that.

Re:Yes and no (4, Insightful)

Thomas Shaddack (709926) | more than 4 years ago | (#32560746)

There are devices harvesting power from ambient sources - vibrations, low-level light, small temperature differences, or, when implanted in an organism, using micropower glucose fuel cells. All these offer very very low power. Designing chips capable of operation with power requirements sufficiently low to be fed from such sources is DEFINITELY not a waste of effort.

Please broaden your perspectives.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32560960)

This proposed research has the potential to get so much grant money for doing what every Electrical Engineer already works towards in current designs.

Pun Intended?

Re:Yes and No (1, Interesting)

Anonymous Coward | more than 4 years ago | (#32562090)

Snake oil? Only if you think it is about global energy preservation. This could be used for extending battery life in cell phones or laptops. If they end up increasing the battery life with 10% or so it will become the new energy saving technology^tm that everyone will use.

Re:Yes and No (1, Insightful)

Anonymous Coward | more than 4 years ago | (#32560096)

Indeed. All scientific research is utterly useless and wasted time unless it has immediate and forseeable tangible benefits.

I have to disagree. The pursuit of knowledge can be rewarding in and of itself. Besides you never when some discovery might prove useful. For example, Boolean logic, which is used to design transistor circuits, was invented in the 19th century. It was pretty useless until transistors came along in the 1950's.

Re:Yes and No (1)

operagost (62405) | more than 4 years ago | (#32564504)

Whoosh.

Re:Yes and No (1)

spazdor (902907) | more than 4 years ago | (#32588016)

Don't look now, but I think you just got doublewhooshed.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32585224)

Indeed. All scientific research is utterly useless and wasted time unless it has immediate and forseeable tangible benefits.

I have to disagree. The pursuit of knowledge can be rewarding in and of itself. Besides you never when some discovery might prove useful. For example, Boolean logic, which is used to design transistor circuits, was invented in the 19th century. It was pretty useless until transistors came along in the 1950's.

whoosh...

Re:Yes and No (1)

Anonymous Coward | more than 4 years ago | (#32560188)

Without fundamental research, no scientific research resulting in tangible results would be possible.
Fundamental research is the basis of all scientific progress.

Re:Yes and No (-1, Flamebait)

Anonymous Coward | more than 4 years ago | (#32560106)

What you claim to believe doesn't matter. This is real research being done, not whatever it is you think you know. This is serious stuff. Are you one of these researchers? No? Didn't think so. Do yourself a favor and get a clue about what you're commenting on before you run your mouth off like this.

Every little bit of energy matters these days, and these people are putting their livelihood on the line for this and you, some "modern geek" who is very unlikely doing this level of significant research, basically says their whole work is bullshit. Prove that you're qualified to make that claim. Show some credentials. People like you probably said that flying or going to the moon was bullshit too. 640K is enough for everyone, don't need to optimize that code because the hardware will catch up, Earth is flat and stars revolve around it, blah blah blah....

The lesson to be learned here is shut your fucking mouth unless you're a qualified authority on the subject. Otherwise, you risk looking like a fool.

Re:Yes and No (1)

Austerity Empowers (669817) | more than 4 years ago | (#32560294)

Not every researcher asking for money is altruistic. Doubt is good.

Re:Yes and No (5, Insightful)

Anonymous Coward | more than 4 years ago | (#32560244)

You're just a fucking ignorant moron.

This has nothing to do with "green" propaganda and raining on your political masturbation parade, and everything to do with looking at ways to overcome the problems that die shrinkage has on causing waste power from static dissipation to prevent further technology advances, you fuck.

The summary is only using "off" in an informal sense. In an idealized textbook transistor model, when the transistor is "off" or in cutoff, it is off completely. But in reality, there is leakage, and so this "cutoff" region actually has some more interesting things going on, then a fucking tool like you apparently would understand. With large transistors in CMOS configurations, there is virtually no leakage and no static dissipation. As features have shrunk, the leakage has become a fully technological advancement problem. It isn't just about treehugging, but also the fact that if you get to a certain point where you have tons of transistors in a small space, if you can't remove the waste heat, you've got a major practical problem.

Get a clue, you useless fucktwit.

Mod parent UP!!! (1)

iammani (1392285) | more than 4 years ago | (#32560366)

Mod parent UP!!!

Re:Mod parent UP!!! (0)

Anonymous Coward | more than 4 years ago | (#32561960)

If I had mod points, I'd mod the post down to encourage intelligence discussion in a civilized manner.

Re:Mod parent UP!!! (0)

Anonymous Coward | more than 4 years ago | (#32562124)

Too fucking right you tool.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32561724)

What he said! (#32560244)

Re:Yes and No (2, Interesting)

operagost (62405) | more than 4 years ago | (#32564558)

It's too bad I just used up my modpoints; because while the parent post has a few good points, I could not in conscience mod up a post that's so full of profanity, ad homs, red herrings, and insults like others have done here. It's difficult to read and letting anger overwhelm a perfectly good argument doesn't serve anyone.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32575494)

It's too bad I just used up my modpoints; because while the parent post has a few good points, I could not in conscience mod up a post that's so full of profanity, ad homs, red herrings, and insults like others have done here. It's difficult to read and letting anger overwhelm a perfectly good argument doesn't serve anyone.

No ad hominem attacks in the grandparent post.

An ad hominem attack would be "your argument is wrong because you're gay."
The grandparent is just saying "you are a fucking idiot."

Learn the difference.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32586958)

Yeah, that kind of attitude gives good Engineers a bad image, all because the original poster didn't seem to read the article.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32560710)

Subthreshold operation is not the same as leakage current. Current in the subthreshold region can be controlled by placing a certain gate voltage on it in much the same way as you would in normal operation mode where as leakage current is not controlled and only happens as a result of the fact that doped silicon its self is in fact a conductor even without a depletion region.

I recall learning about subthreshold operation of a MOSFET in my VLSI design class and the current in this region can be controlled, however, it is not as predictable as it is in other regions of operation. Subthreshold current tends to follow a logarithmic scale when small voltages are applied, but this tends to change a lot depending on the fabrication process that is used so usually experimentation is needed to achieve the desired results.

This is not news, it has been being done for years.

Re:Yes and No (0)

Anonymous Coward | more than 4 years ago | (#32562168)

I have worked at IMEC, well let me tell you they are not the kind of guys publishing useless concepts just to get government grants (hint: they're almost entirely financed by their industrial partners, the list of which you should have a look at).
The kind of low-power applications they are targeting are obviously embedded devices, especially for medical applications - which is one of their driving axis - as underlined by another AC a few posts down. Believing that one could even think about significantly reducing world's energy consumption with ultra-low-power logic transistors kind of... shocks me. But well, it's /.

Re:Yes and No (1)

Bender_ (179208) | more than 4 years ago | (#32571174)

This has nothing to do with "leakage" current. As basic field effect transistor theory will teach you, there is a region below the threshold voltage [wikipedia.org] where the current depends exponentially on the gate bias. Yes, exponentially instead of linearly or quadratically as in the "on" region. This means that small changes in the gate bias will allow for a huge change in current. The drawback is here that we are talking about extremely low current. In CMOS logic this equals lower operation frequency.

This idea here is to build circuits that are extremely power efficient but also extremely slow. As mentioned in the article, potential applications may include wireless sensor networks that have to operate on extremely low energy.

Not news (3, Informative)

betterunixthanunix (980855) | more than 4 years ago | (#32559944)

I heard about this research topic over a year ago when I took VLSI. The main problem, as I understand it, is not building circuits that operate below the threshold voltage, but actually reading the output of those circuits.

Re:Not news (2, Insightful)

LynnwoodRooster (966895) | more than 4 years ago | (#32560658)

No problem! See, you just add a higher voltage rail, and then use that to run the output transistors so you get readable outputs!

.
Oh wait...

Re:Not news (3, Interesting)

tehSpork (1000190) | more than 4 years ago | (#32560696)

Same here. I took VLSI Winter 2009 and we spent an inordinate amount of time studying and working on sub-threshold designs. Part of our final project (and final exam) was to produce a simulated and laid-out circuit using a sub-threshold supply. It's not very complicated, you just lower your clockspeed and source voltage, most of your existing circuits work just fine. The major problem is that they are now working at very low clockrates (KHz as opposed to MHz) which doesn't make too many people very excited.

Re:Not news (3, Informative)

nerdbert (71656) | more than 4 years ago | (#32564656)

It's been "not news" now for at least 20 years. Tsvidis did significant work on subthreshold FETs for neural networks back in the 80s and early 90s. Subthreshold design isn't common, but it's by no means a new field.

Subthreshold has its place, but it's not a pleasant place to work. Mismatch between transistors is about 4x higher, gate leakage is a huge factor below 130nm, the models you get from your foundry aren't reliable or accurate, etc.

I make subthreshold circuits all the time when I need bandwidth and have no headroom (hello 32nm, how unpleasant to meet you when doing analog design!). But I'm not doing low power subthreshold design, rather it's for very, very, high speed analog signal processing designs.

pffft not likely (1)

Simmeh (1320813) | more than 4 years ago | (#32559948)

I know when I'm off theres no chance of me workin...

"Off and off-er" or "off and almost-as-off"? (4, Interesting)

dpilot (134227) | more than 4 years ago | (#32559982)

As we've scaled deep into the submicron region, it's been getting harder and harder to turn the devices really "off". Leakage current has been rising and has been quite noticable for several generations now.

So the idea of doing useful work with subthreshold current sounds neat
(OK, I just went and read TFA.)

Still sounds neat, but...

In deep submicron part of the reason for the subthreshold leakage problems is control of Leff. (The effective channel length of the FETs.) There's a thing called "line length variation" which means that channel lengths in different parts of the chip will be different, sometimes subtly, sometimes not so subtly. Threshold voltage (Vt) is a strong function of channel length, making subthreshold leakage also a strong function of channel length. Performance characteristics will vary widely across the chip, likely much more than conventional transistor operation.

This will make it tough to scale down, (in feature size) scale up, (in chip size) and make manufacturable.

Heh, reminds me of something... (1)

NotQuiteReal (608241) | more than 4 years ago | (#32560408)

"Off and off-er" or "off and almost-as-off"?

Reminds me of - It depends on what the definition of the word 'is' is

Which of course leads to the arch typical;

"When I use a word," Humpty Dumpty said in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less."

Re:Heh, reminds me of something... (1)

spazdor (902907) | more than 4 years ago | (#32588434)

Off and off-er? I 'ardly know 'er!

Re:"Off and off-er" or "off and almost-as-off"? (1)

Bakkster (1529253) | more than 4 years ago | (#32564242)

In deep submicron part of the reason for the subthreshold leakage problems is control of Leff. (The effective channel length of the FETs.) There's a thing called "line length variation" which means that channel lengths in different parts of the chip will be different, sometimes subtly, sometimes not so subtly. Threshold voltage (Vt) is a strong function of channel length, making subthreshold leakage also a strong function of channel length. Performance characteristics will vary widely across the chip, likely much more than conventional transistor operation.

This will make it tough to scale down, (in feature size) scale up, (in chip size) and make manufacturable.

Right, hence why nobody has done it in any quantity yet. I assume this research will find some balancing point where process variation's effect is negligible. For example, if the range for a strong '0' is 0-0.04V and a strong '1' is >0.26V, then you just need to ensure that process variation puts that subthreshold level somewhere between 0.04V and 0.26V, probably significantly so. If process levels can keep that subthreshold level between 0.1V and 0.2V, that might be good enough.

It will be interesting to see the ideal number of line buffers change from being based on transition time to load resistance.

Oh, for crying out loud (3, Informative)

overshoot (39700) | more than 4 years ago | (#32560002)

Transistors in weak inversion have higher higher transconductance/current ratios than transistors in strong inversion do. Using MOS devices in that mode is standard operating practice for a whole host of applications.

Notable among those applications are ... wristwatch chips. Eric Vittoz has made a career of this mode of operation. You can't set foot in the subject without running across patents, books, articles -- Hell, probably recipes by him going back 40 years.

Germanium transistors are new tech again? (0)

Anonymous Coward | more than 4 years ago | (#32560034)

Germanium transistors predate silicon and have just as low a voltage drop and have a high leakage current.

Next generation of efficiency gains? (1)

ksandom (718283) | more than 4 years ago | (#32560064)

The thing that popped into my mind while reading this was the possibility of this being used to operate the entire system at this level (rather than just making use of leakage). If it could perform fast enough, this could potentially massively reduce power consumption, and thus the need for cooling as well.

How to extract body heat and save the world (3, Funny)

Anonymous Coward | more than 4 years ago | (#32560076)

A male genitalia heat extraction device. Power devices and increase the dismally low western world sperm count in one.
Not patented yet because I don't know how to make one. Someone do it!

Re:How to extract body heat and save the world (0)

Anonymous Coward | more than 4 years ago | (#32560856)

Not patented yet because I don't know how to make one

When has that ever stopped anyone?

Re:How to extract body heat and save the world (0)

Anonymous Coward | more than 4 years ago | (#32561544)

I wonder what percentage of /. still remembers the "laptop burning your penis" meme.

Examining the edges. (1)

amanicdroid (1822516) | more than 4 years ago | (#32560090)

Sounds awesome. Good luck scientists!

NEAR threshold tends to be lower energy (5, Informative)

Theovon (109752) | more than 4 years ago | (#32560092)

Another commenter is correct in pointing out that what they're doing is using leakage current. When we measure power dissipation, we count two things, (a) dynamic power, which is used when a transistor switches and is a function of frequency, voltage, and temperature, and (b) static (leakage) power, which is always going on and is a function of voltage and temperature. At 180nm, the ratio of dynamic to static was about 1000:1. It started to become noticed at around 90nm and a problem at 65nm. Now at 45nm and 32nm, leakage is about half the total power usage. The best way to lower power is to reduce voltage, but this kills performance scaling. Scaling down transistors reduces dynamic power but increases relative static power, which is why processors like the Core i7 use not just clock gating but POWER gating, dynamically, at a functional unit level.

Regarding subthreshold, as you lower voltage, power goes down. The problem is that transistors also get slower. Above threshold, the power goes down faster than speed, so if you're using a transistor with threshold voltage of 150mV with a supply voltage of 300mV, you get like a 100th the power dissipation, but a tenth the speed, which means that you use one tenth the energy to perform some process. As you lower the supply voltage below threshold, the transistors get slower faster than the power goes down, so total energy actually goes up as you lower voltage below a certain point. There is a supply voltage point either side of the threshold voltage where energy is minimum for the range. You use near threshold or sub threshold depending on if you care about speed. Also, things behave quite differently at low voltages, so you have to change all your design techniques.

One of the problems with near and sub threshold is that you don't actually know what your threshold voltages are anymore. It's called process variation. The transistors are so tiny that you get on the order of tens of dopant atoms per transistor. The doping process is highly random, so you get wide variance on threshold voltage (and effective channel length too), meaning that two transistors next to each other have different switching characteristics. This is actually a major problem at 32nm, resulting in unfortunately large supply voltage margins to avoid timing-related errors, which translates into excessive power usage. It's an even bigger problem when the supply is near the threshold (above or below), because the speed of a transistor and its power output are actually functions of the difference between supply voltage and threshold voltage. If the supply is 300mV, then the transistor with Vth=130 is going to be way faster (and way leakier) than the transistor on the same die with Vth=170. Of course, both were designed to have Vth=150, but you can't control that well enough.

My area of research involves coping with the 5X decrease in reliability at NTC, and I'll talk more about it when my papers are accepted. :)

Re:NEAR threshold tends to be lower energy (5, Funny)

Ethanol-fueled (1125189) | more than 4 years ago | (#32560354)

Now these are the kind of Slashdot posts that make my dick hard.

I ponder ... (1)

freaker_TuC (7632) | more than 4 years ago | (#32562796)

which kind of sites you consider to be .. "porn".

No, thinkgeek is NOT a pornsite!

Re:I ponder ... (1)

thousandinone (918319) | more than 4 years ago | (#32568354)

I beg to differ... [thinkgeek.com]

Re:I ponder ... (1)

freaker_TuC (7632) | more than 4 years ago | (#32576996)

Great idea for an useless USB device!

Although, it says USB Devices .. not Orifices ..

Re:NEAR threshold tends to be lower energy (0)

Anonymous Coward | more than 4 years ago | (#32561538)

Will you marry me?

Re:NEAR threshold tends to be lower energy (0)

Anonymous Coward | more than 4 years ago | (#32561750)

Funny, I co-authored a paper about exactly the same thing and it's also being reviewed.

I wonder if you work for the other organisation whose name also starts with an i as I knew a guy who was doing the exact same thing there.

Wish you the best mate and hope we can read each other soon!

Nothing new (4, Interesting)

eudean (966608) | more than 4 years ago | (#32560152)

As far as I know (i.e., according to some professors I've spoken to), transistors in devices with extremely long battery lives, such as hearing aids and watches, are typically operated in sub-threshold in order to conserve power. Of course, these devices are also typically not speed-critical. A lot of biomedical applications probably fall under the umbrella of requiring low power (for battery life and/or thermal reasons) and not requiring high speed, making the application a natural fit for sub-threshold operation.

Been around for ages (2, Informative)

AndOne (815855) | more than 4 years ago | (#32560218)

Using transistors in sub threshold modes has been around for ages. Carver Mead proposed their use for modeling neurons in silicon ages ago and there have been others who use these techniques for other low power techniques. See Delbruck(Zurich ETH) or Boahen(Stanford/Penn) or Andreou(Johns Hopkins). Two of my undergrad profs did thesis work at Georgia Tech using these techniques as well to do neuromorphic engineering tasks.

Re:Been around for ages (0)

Anonymous Coward | more than 4 years ago | (#32560412)

Indeed, Carver also taught classes on the subject for years, in which the students would design subthreshold chips that would then be fabbed and tested.

This is nothing new (4, Informative)

blue_moon_ro (973863) | more than 4 years ago | (#32560220)

This is nothing new, this behavior of the CMOS transistors in the subthreshold region of operation has been known for years. I actually wrote a paper 5 years ago on a circuit using transistors in the subthreshold mode of operation. As always, there are trade-offs, and the main one is that the frequency of operation is a lot lower than if the transistor would have worked in the normal region. The main advantages of running the transistors in this operating region are low power and the fact that the current vs. voltage law changes from the quadratic law in the regular operating region, to exponential here, i.e. I ~= e^[n(VGS-VT)/kT] (see Sedra&Smith's or any other reference electronics book). So don't dream of your next low power processor using this technology. This is more suited for analog applications (one of the first ones that I remember is current multipliers and low-power current-mode analog circuits) and this is how these guys at IMEC seem to be actually using it.

Re:This is nothing new (1)

lazyDog86 (1191443) | more than 4 years ago | (#32560358)

Yep, that's exactly right and I still find it amusing the everything-old-is-new-again of the fact that the exponential behavior described here mirrors the characteristics of the old high-power bipolar technologies. So we need to dust off our old bipolar engineering texts to start working in the brave new world of low-power design.

Seriously though, this is a niche analog technology for a small, but important market. I imagine it will always be the realm of small volume, high margin products.

Re:This is nothing new (1)

Bengie (1121981) | more than 4 years ago | (#32560552)

kind of like how we went from serial to parallel back to serial interfaces with computers? :P

cut off transistors (0)

Anonymous Coward | more than 4 years ago | (#32560330)

RF and Audio circuitry has always used transistors in the cut off state. Detectors, class B, C amps, etc are examples. Most of what I know about is analog which is mostly history. There probably are applications that could utilize this technology however, as I remember the cut off region was very non-linear and work great for detectors. Maybe you could make a quad core cut-off processor that works great as an am radio detector!

I don't know anything about electrical engineering (2, Interesting)

The Clockwork Troll (655321) | more than 4 years ago | (#32560558)

Forget the P = NP question - does PNP = NPN?

Re:I don't know anything about electrical engineer (0)

Anonymous Coward | more than 4 years ago | (#32561190)

No.

Re:I don't know anything about electrical engineer (1)

Talisein (65839) | more than 4 years ago | (#32561438)

You would be closer to say PNP = -NPN. Especially if you carefully define the - operator.

Re:I don't know anything about electrical engineer (0)

Anonymous Coward | more than 4 years ago | (#32570614)

Just remember, P = NP for sufficiently exotic definitions of '='

Old is new again, again (1)

Ancient_Hacker (751168) | more than 4 years ago | (#32560646)

Funny, but I was just reading an old radio magazine, circa 1938, where they were using 5 to 6 volts to the heater of a rectifier tube that usually needed 25. That's 1/4 the voltage, about 1/16th the power, and the rectifier worked BETTER at detecting radio signals than at full voltage. Some complex thing about the diode work functions one might suspect.

Engineers have explored most corners of the performance envelope, nothing all that new under the sun.

Bipolar trabsitors are only "off" at zero volt (1)

gweihir (88907) | more than 4 years ago | (#32560682)

The current into the base of a bipolar transistor has a logarithmic relationship to the BE voltage. That means it is only really off when the base voltage is exactly zero. This makes the article title BS.

Re:Bipolar trabsitors are only "off" at zero volt (1, Insightful)

Anonymous Coward | more than 4 years ago | (#32561204)

The current into the base of a bipolar transistor has a logarithmic relationship to the BE voltage. That means it is only really off when the base voltage is exactly zero.

These are MOS devices, which have a squared voltage/current relationship between the gate and source when operated below the threshold voltage.

I wrote my thesis on this stuff in 1994, and I used a textbook called "analog VLSI" written by Carver Mead at Caltech. There are commercialized cochlea implants available that use this technology. This has got to be the most non-news story I have come across for a long time.

Re:Bipolar trabsitors are only "off" at zero volt (0)

Anonymous Coward | more than 4 years ago | (#32562244)

Except neither the title nor the article are actually about bipolar transistors, but MOSFETs...

Re:Bipolar trabsitors are only "off" at zero volt (1)

ChrisMaple (607946) | more than 4 years ago | (#32564072)

Bipolar transistors have the additional advantage that there is no difficulty in controlling a threshold voltage; the equivalent (and less significant) problem is controlling current gain. Bipolars have the disadvantages that any active circuit must always draw current, and bipolar logic is more complex than CMOS. One correction to your comment: the current in a bipolar transistor is exponentally related to Vbe, so performance degrades very rapidly with decreasing voltage. Multiply speed by about 0.02 for each 0.1 volt drop in Vbe when fully turned on.

Low power decisions (2, Interesting)

PingPongBoy (303994) | more than 4 years ago | (#32561130)

The goal of low power transistors is reasonable, but a new transistor design may be needed. The brain can do a lot of operations with little power but in terms of clock speed, the brain isn't that fast. A similar design may be good for low power electronic decisions - massive number of circuits at low frequency.

Re:Low power decisions (1)

Talisein (65839) | more than 4 years ago | (#32561486)

A more important property of the brain is that it is not as precise as a computer. The brain, and many other biological computations, perform their calculations in an analog manner that usually gets them "close enough" to the right answer. Digital designers think they need every bit of precision in a 64-bit floating point computation and they engineer the circuit to require it--this involves a lot of "over engineering." Of course, the really cool thing is that biology has "digital" circuits as well, when it needs it!

I'm not really an expert, I've just attended a lecture by Prof. Sarpeshkar at MIT. He's built some cool DSP devices modeled after the human ear [mit.edu] . He has a new (text)book, "Ultra Low Power Bioelectronics: Fundamentals, Biomedical Applications, and Bio-inspired Systems."

It's really fascinating stuff, and I think is where low-power computation is really going to go: into a hybrid analog-digital domain. Subthreshold is cute in SPICE, but process variation is a huge barrier to using it on any kind of microprocessor or SoC sized chip.

Hard Process Metric to Control (1)

macs4all (973270) | more than 4 years ago | (#32561248)

This technique will probably require much tighter control over some figures of merit (specs) that are traditionally not that tightly controlled. For example, junction capacitance and resistance, as well as the thickness of the junctions themselves, will have to be elevated to a level of process-control precision that will likely make this a laboratory curiosity for a while.

Old (0)

Anonymous Coward | more than 4 years ago | (#32561304)

Just to Chime in with Everyone saying this is old, I work with a professor who does subthreshold digital circuit design almost exclusively as his area of research. I'm an undergrad, but I read a paper by one of his grad students recently, the guy designed an FPGA that operates entirely in subthreshold. Just google it, you'll find stuff.

Re:Old (1)

Talisein (65839) | more than 4 years ago | (#32561562)

Research in the area is definitely ongoing, but the article summary presents such a basic overview that it makes it sound like subthreshold as a basic premise is some kind of new idea.

Now a subthreshold FPGA, that's nice if the interconnect is kept at the same low voltage. But then it would take a *really* long time to communicate. Although I guess you can throw in some sense amplifiers. But if the interconnect is high voltage, then it remains the major source of power loss. Is your Prof John Lach? I can't get to the seeming paper on my IEEE student account.

Already done, why is this news! (0)

Anonymous Coward | more than 4 years ago | (#32563070)

Sarpeshkar has been doing this for a while now. He teaches a good class on it:

http://www.rle.mit.edu/avbs/schedule.html

Oldish News (0)

Anonymous Coward | more than 4 years ago | (#32564644)

This isn't really anything new. Sub-threshold circuits have been being researched (and built!) for several years. I had some experience with them in some graduate courses I took when I was finishing up my undergraduate EE/CPE degrees last year. They actually are not that much more complicated than traditional CMOS, and the circuits basically end up looking the same (at least inverters, NAND's, etc.).

Since you are dealing with much less charge per unit time, it just takes a lot longer for the devices to operate. Since power consumption (switching power) is related to voltage in CMOS circuits as V^4 (that's not a typo, and I'm not talking about P=IV), sub threshold circuits allow for extremely low power consumption for the albeit slow speeds that they operate at.

When you think about sub VT circuits and the technologies that we work with now (like 32nm), the uses for this technology are profound. I know that at my alma mater there was lots of research into using sub VT technology for chips embedded into your body and for sensor networks. These chips require so little power that there was lots of talk and research about using energy that your body produces like heat to power these devices instead of relying on batteries which need to be replaced. Pretty cool stuff, in my opinion.

Anonymous Coward (0)

Anonymous Coward | more than 4 years ago | (#32566618)

This is not new, Carver Mead first proposed this many years ago it is been used to develop micro power VLSI circuits. The main problem is the transfer function of the active region is not linear but exponential. This creates some interesting problems for traditional transistor design. Look up neuromorphic engineering for further reading.

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