DARPA Creates 0.85 THz Solid State Receiver 84
hypnosec writes "DARPA, under its THz Electronics program, has designed a solid state receiver capable of THz (terahertz) frequencies thus inching towards the possibilities of transistor-based electronics that will operate at THz frequencies. The newly designed solid state receiver demonstrates a gain at 0.85 THz. This particular milestone is a stepping stone for the next target of 1.03 THz. Because of this achievement a host of DoD electronics capabilities can now be realized. One such application where this can be of use is for a sensor that will operate through clouds under a DARPA program dubbed VISAR."
Nakedcams! (Score:3)
Re:Nakedcams! (Score:5, Funny)
I also have a THz wave receiver. It's called "eyes".
I also have this device capable of producing THz waves. It's a lamp.
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Yup. THz. What he said.
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There's rather a lot of difference between 0.85 THz and 500 THz. A similar factor increase in frequency from visible light would give you X-rays, and I doubt you'd say they were the same as visible light.
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Personally, I use my skin to detect most THz radiation, some call it "temperature sensitivity"
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Somehow I doubt people would be spending hundreds of millions of dollars on THz detectors and related technologies if it were no different from conventional visible/IR imaging.
Sure, EM is a continuous spectrum from ELF to gamma rays. That doesn't mean that a two mile long antenna suitable for the former is going to detect gamma rays.
EM in the 1-10THz range has a lot of interesting applications, and currently our ability to manipulate it is very limited, compared to what we can do with radio or with IR/visi
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Where did I say that this article had anything to do with detectors? I said that people were spending lots of money on THz detectors, which is true. The argument was that working with THz radiation wasn't anything unusual, and my point was that the reason people were spending all kinds of money on the technology were doing so because it was.
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Opening a band-aid wrapper gives off visible light - try it in a dark room sometime.
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Well within the 1-999 boundary before it hits the petahertz.
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Yes! When can I buy those X-ray glasses that were advertised all over the place in the SciFi pulps?
I never ordered one because I knew enough about science that it must be a scam, but now we can finally do it!
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Instead of buying X-ray glasses back in those days, I made my own. I got some plastic with a ribbed surface on one side, and placed two sheets with flat sides back to back. I cut them to fit some empty glasses frames. I had a few of my friends actually fooled that the double-imaging effect seen through them were parts of people's bones inside.
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Wait, what? There was a real optical effect going on? I always thought they were just wacky designs with holes in them so you can see the other people at the halloween party...
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That could also be used for transmission purposes.
Re:Is this just for communications? (Score:4, Insightful)
... or are they going to try to make a CPU/GPU core at this speed?
In the long run, maybe. In the short run you aren't going to like it. A very stereotypical microwave LNA MMIC operating around a factor of 100 lower then this device frequency (in other words, cheap and off the shelf) consisting of a couple transistors is biased much like a LED... couple volts, couple dozen mA. Lets call it 4 volts at .040 amps thats 160 milliwatts per device. For rounding purposes lets say a tenth of a watt per transistor. So if you have a roughly quarter million transistor original 386 a 10 GHz discrete 386 made out of microwave transistors would draw about 30 or so KW. Which is quite a lot of power. Of course you don't need low noise small signal performance or great fan in / fan out ratios... Regardless high speed individual devices certainly like their DC power.
The problem with making processors fast is keeping them fed with something to do. CPU tech always seems to lead memory/IO/algorithm design, I can't remember an era when the "memory guys" were waiting on the "processor guys" to catch up. With current tech a 1 THz CPU would merely spend 99.9% of its time in idle waiting for memory... But nothing in the world could run a NOP or an endless loop faster than that device.
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I'm not expecting some CPU at the capacity level of an x86 or even ARM chip. Something smaller would make sense. Very basic instruction set, few registers, no floating point, just something to provide logic control that can make decisions at rates above what today's host computers can barely get a clock pulse at. Maybe at best an 8-bit architecture, if even that.
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With current tech a 1 THz CPU would merely spend 99.9% of its time in idle waiting for memory... But nothing in the world could run a NOP or an endless loop faster than that device.
This is incorrect, common DDR3 memory is already 2 orders of magnitude slower than a 3 Ghz CPU and they work just fine.
With a THz CPU you also have THz memory (registers, level 1 cache, etc.), if your algorithm fits in the cache you will have close to 100% of the performance.
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How compares the CPU die size with the distance that the signal travels at this speed ? Right.
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Its a design issue. You won't like it because its a PITA. Google for "Peristaltic Array" and apply it to cpu components/microcode instead of the somewhat more popular higher level implementation. Theres about a zillion other high performance computing ideas, mostly unchanged since the 60s and 70s (although continually reimplemented up to current time)
I designed and simulated (in MS basic) a system like this many years ago for fun that operated at KHz speeds (reimplementing in the then unheard of GHz rang
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Which is why I didn't jump to the assumption it could just be used for digital purposes immediately. But, nicely linear analog is hard to do. There may be non-linear leftovers in the research.
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All digital electronics is ultimately analogue. If you had transistors that could run at that speed, you could probably sample at (at least) a quarter of that speed. Make a very nice ADC/DAC for a software (de)modulator and fixed function DSPs.. Lots of digital applications on the digital side, if the power draw is reasonable.
typo (Score:1)
It's "gain at 0.85 THz", not "of".
Re:typo (Score:5, Funny)
This is Slashdot, not Wikipedia.
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...and neither is a trustworthy authority on anything.
Re:typo (Score:5, Funny)
From the comments, I thought this was youtube...
Re:typo (Score:5, Informative)
Incorrect. Gain is unitless (Vout/Vin), and decreases pretty much proportionally to the inverse of the frequency on amplifiers, so chip makes use something called the Gain Bandwidth Product (GBP) instead of the 'pure' gain, because it is a much more useful number for specifying actual transistor/amplifier performance in real live working conditions. And the unit of the GBP, is, you guessed it! Hz. Thus, a transistor with a GBP of 0.85THz will have a gain of 1 at 0.85THz, a gain of 2 at 0.425THz etc. When I see a gain with units in Hz I subconsciously think 'GBP' and don't even miss a beat...
See http://en.wikipedia.org/wiki/Gain%E2%80%93bandwidth_product [wikipedia.org] if my explanation doesn't make sense.
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You're incorrect sir. The Slashdot summary misquotes the linked DARPA press release which clearly states "gain at 0.85THz".
Gain-bandwidth product is mostly used for opamps because a given opamp could be put into an amplifier circuit with negative feedback which is either low gain and high bandwidth, or high gain and low bandwidth, and each circuit would have the same gain bandwidth product. For microwave/mm-wave amplifiers where 10dB of gain might be a luxury and most circuits don't make use of negative f
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You don't need negative feedback for there to be GBP. GBP is pretty much just another way of measuring slew rate given a fixed amplitude.
But still, the DARPA press release says "first solid state receiver to demonstrate gain at 0.85 terahertz", so each the entire circuit may just have a gain of 1.0001 for all we know... They might have just been aiming for 0.9THz but got a gain of 0.8, so they lowered the frequency until the transistor slew rate was able to keep up with the signal. And a 10-stage LNA means
Gain AT 0.85THz, *NOT* gain OF 0.85THz (Score:3)
Sorry, EE major and I get annoyed reading this kind of thing...
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What they actually should have said was a Gain Bandwidth Product of 0.85THz, but I'm guessing somewhere along the line a journo said something like "Hey my EE friend, what does GBP mean? I've never heard of it, is there anything simpler?" To which the EE friend replies, "It's basically just the gain."
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Nope, DARPA press release clearly states "gain at 0.85THz". The purpose of this program is to push ahead the maximum frequency to enable terahertz radar, so they're shooting for frequency more than GBP.
Anyway, GBP's of over 1THz have already been achieved in the fiber optic communication arena but at frequencies up to ~50GHz, not 850GHz.
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At that frequency what would be the range of such a radar, except in more exotic conditions like transmitters at very high elevation or in deserts? I would think that atmospheric absorption would be a big problem.
Maybe for air-to-air radar it might be practical - once the transmitter is at altitude the absorption of moisture would be less of an issue.
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Range is a problem with THz partly because of the atmospheric loss but also in large part because the achievable transmit powers are so low. The benefit of THz is that it can penetrate things like dust, good for radar imaging in the desert, and it can also penetrate clothing, good for imaging you in the airport ;)
What DARPA is building now is not going to be a field-ready unit, it will be a demonstration piece that pushes the state of the art forward to inform future work in the area.
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The prefix "micro-" in "microwave" is not meant to suggest a wavelength in the micrometer range. It indicates that microwaves are "small" compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.
--From Wikipedia
All for war (Score:1, Insightful)
Here is what they want this for:
This revolutionary advance would give U.S. warfighters an advantage in an especially challenging portion of the RF spectrum
As per usual, it's all for war, it's all that government is interested in.
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Even the hint that a certain technology may have military applications is the surest way of getting large amounts of money to continue the research. Plus there is another world war on the horizon that will make WW2 look like a pillow fight. It's unavoidable to pretend otherwise. All those shouting "can't we all just along" will be the first killed. Should be the ultimate reality show.
!THz (Score:1, Offtopic)
Slow progress. (Score:5, Informative)
Another terrible article summary.
In 2010, a solid-state device at 0.67THz was achieved. [irconnect.com] In 2012, that effort is up to 0.85 THz. Progress is slow, but continuing.
Diode-type CMOS imagers for terahertz radiation [laserfocusworld.com] have been built. Those convert terahertz radiation into DC, which can then be amplified by standard techniques. But diodes don't have gain. That's why the original article emphasizes that this new device has gain.
There are terahertz lasers, waveguides [sandia.gov], antennas, and other components that work up there. The situation is much like radar during WWII; there were a few components that could do specific things at radar frequencies (then 60MHz to 1.2GHz), but general electronics wasn't there yet. Most of the electronics in radars of that period ran at far lower speeds. They still worked.
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We've had THz tube sources for a loooong time. Vacuum tubes let you play with electrons and fields in ways not possible with solid state. Tube-based sources have been pumping out the high frequency waves since a long time.
http://en.wikipedia.org/wiki/Backward_wave_oscillator [wikipedia.org]
Congratulations on not thinking that "solid state" means "no moving parts". Vacuum tubes have no moving parts either.
Gain is nothing withou linearity (Score:1)
It may have demonstrated 0.1dB of gain at 850GHz (seriously, let's not label it THz unless it actually makes THz), but unless it is linear, it is pretty useless for digital communications.
Here's some more technical info/guesses (Score:3)
The summary and linked press releases are light on details so here is what I gleaned from the photograph of the chip based on some experience in the area of microwave/mm-wave device and circuit work. There will probably be much more technical information in upcoming papers in the research literature.
Based on the photo of the chip on the linked DARPA page [darpa.mil] this is not a receiver, but a low-noise amplifier (LNA) which would be used as the front-end for an imaging sensor or communications/radar receiver. It would be straightforward to turn this into an imaging detector at this point by adding a detector after the LNA though I don't think this has one. For a synthetic aperture radar more circuits will be required, especially a mixer to downconvert the frequency.
The slashdot summary misquotes the article saying that the circuit has "gain of 0.85 THz" but should say "gain at 0.85 THz". The LNA appears to have 10 amplifications stages which is very large for a LNA, which suggests that the gain per stage is still quite low at 0.85THz. This is to be expected as the best per-transistor gain cutoff frequencies are not too far 1THz that I'm aware of. The circuit also appears to be built in coplanar waveguide (a metallized signal strip in the middle surrounded by two ground strips) which is easy to fabricate and good for a research environment but it has a higher loss than microstrip (a signal line above a ground plane).
Anyway that's my 2 cents.
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The purpose of the DARPA program is to build a SAR, this LNA will likely be the frontend. There already exist diode mixers which can coherently downconvert 850GHz but the noise figure is bad. With this LNA at the frontend they should be able to mix it down with existing diode mixers or with fancier mixers without too much trouble.
I'm wondering of course how they'll be getting their transmit power - power at 850GHz does not come cheaply.
Oooo THz (Score:1)
Just like me, I have mega-bucks. 0.000002 million bucks in my pocket right now! If I put it in the bank, with interest it will have gain.
TeraHz receiver (Score:2)
So this thing can receive signals at (just less than) a TeraHz... But is somebody transmitting on that frequency?
Obviously the higher the frequency the more bandwidth is available but what about the characteristics of the atmosphere ? Is this for long distance communication? wouldn't clouds etc screw it up?
Government (Score:2)
When a government agency funds something that works, the headline is always, "NASA builds this..." or "DARPA builds that..."
But when a government agency funds something that doesn't work, the headline instead is, "Lockheed mess up this..." or "Boeing messed up that..."
Did DARPA "create" this as the headline says, or did they just fund somebody else to do the research, design and implementation?
http://www.laserfocusworld.com/articles/2012/07/northrop-grumman-demos-850-ghz-integrated-receiver-circuit-aiming-a
VISAR perhaps influenced by VISOR (Score:2)
Geordi La Forge's VISOR allowed him to see between 1 hz and 100,000 THz. Isn't it kinda interesting that they used a name so similar?
wow... (Score:2)
When I was doing war toys, not all that long ago, (ok, I guess it was. Where did the time go?) 40 Ghz was considered really, really high.
A curious advantage (Score:2)
"VISAR seeks to develop and demonstrate a targeting sensor which operates through clouds as effectively as today’s infrared (IR) sensors operate in clear weather. This revolutionary advance would give U.S. warfighters an advantage in an especially challenging portion of the RF spectrum.”
The wars of the future will not be fought on the battlefield or at sea. They will be fought in space, or possibly on top of terahertz waves.
Get back to me when (Score:2)
it goes to 11.
Yes, I joke there. I do find it fascinating how stuff keeps getting pushed to the limits, and then we say "bah, we can do better!"