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Chip Power Breakthrough Reported by Startup
Carl Bialik from WSJ writes "The Wall Street Journal reports that a tiny Silicon Valley firm, Multigig, is proposing a novel way to synchronize the operations of computer chips, addressing power-consumption problems facing the semiconductor industry. From the article: 'John Wood, a British engineer who founded Multigig in 2000, devised an approach that involves sending electrical signals around square loop structures, said Haris Basit, Multigig's chief operating officer. The regular rotation works like the tick of a conventional clock, while most of the electrical power is recycled, he said. The technology can achieve 75% power savings over conventional clocking approaches, the company says.'"
Conventional electronics uses circular loop structures to send electrical signals as the electrons would get caught on corners that were too sharp. These people must have overcome that limitation.
Why not? If this works it sounds like Moore's law would continue, and would give whatever company that deployed it first a performance advantage.
Because first they're going to get a bunch of their theoreticians to work the math on the problem to make sure it's viable. Then they're going to get a bunch of their VLSI modellers to run virtual simulations on the clock modification to refine exactly how great the potential efficiency gain would be. If that turns out OK then they'd produce some simple mock-ups of the new clock architecture to make sure that it functions correctly in hardware. Then they'd go about the expensive and time-consuming process of redesigning the current chip architectures to include the new style clock. Then they'd produce an initial fabrication of the chip to run through extensive hardware testing (and on the inevitable failure they'd hop two steps back and try again.) Once they were happy with the design they'd scale up to full production and roll it out.
Everybody in the microprocessor design world remembers this all too well.
The gift of death metal does not smile on the good looking.
It just amazes me that a small, never-before-heard-of-company offers a solution to a problem that Intel, IBM, and AMD have been trying to solve for over a decade, each of which have 10 times the budget, expertise, and personel. Did I mention a headstart of a minimum of 10 years of R&D tossed at this problem? I hate to be a pessimistic troll-like poster, but without even a working proof of concept, I can only call this vaporware until they show me a working product. This article says nothing except "we have technology every computer in the world will need in the next ten years... please invest in us and we'll get you a demo soon."
I've read the FA and despite having a couple of CMOS designs behind me I don't understand a bit of what they are saying. Either the reporter that wrote this has absolutely no idea what he is writing or this entire 'breaktrough' is just vapourware.
The article seems to say that the 'tick' of the clock is carrying energy throughout the chip and when the 'tick' hits the edge, the energy is lost. Electronics in your typical digital circuit does not work that way. Energy does not flow through the chip with the signals (ok, it does theoretically, but that amount is negliable with the dynamic losses in the gates mentioned below).
You get power dissipation in each gate or buffer that changes state because of some signal, irregardless of the direction in which the information is flowing. You can not recycle this power. This comes directly from the basic principle behind CMOS technology (used by almost all digital chips today) - you are charging and discharging a capacitor.
Typical example, that running signals in a circuit does not save power: take a ring oscillator (a number of negators wired in a loop). This circuit will oscillate (send changing signals through its loop) and consume an considerable amount of power.
P.S. In this context, the correct spelling of nerd is E-N-G-I-N-E-E-R ;^)
In most respects, chips today are ALREADY 3d in that there are multiple layers of planar (flat layers) metal wiring (anywhere from 4 to 8) connected by vias (vertical interconnect) over a single layer transistors. The routing of signals on each layer is on purpose designed to be a crazy-ass network (to avoid electromagnetic signal coupling noise between adjacent wires).
However, in current technology, there's still only 1 layer of transistors, and the main limitation of adding more is that there's no good way to get rid of the heat of transistors. Even today, there isn't a good way to get rid of the heat of the transistors in the 1 layer of current chips, let alone a big pancake stack (or lasagna) of transistors. People are already starting to stack memory chips that don't get too hot together, and I'm sure they'll eventually start doing different kind of stacks too as they get better at figuring out the heat problem...
The press has a knack for distorting stories and making it very hard to figure out real technical details.
http://multigig.com/pub.html has some whitepapers. I read the ISSCC 2006 slide set, which let me know the general technique.
Basically, they produce a clock ring to produce a "differential" clock pair that after one lap swaps neg and pos and so it's frequency is tuned by it's own capacitance and inductance. They call it a "moebius" loop since it's not really a differential pair, but the clock wave makes two round trips before getting back to the start.. Neighboring loops can be tuned together (although if that's by just routing the wave throughout the chip I'm not sure). They didn't seem to mention synchronizing the period to outside sources, and I'm not sure how they'll be able to do that.
The clocking is not the interesting part to me, but rather their logic strategy. The trick is that logic itself has no connection to power or ground. The clock nets provides the "power and ground" and all logic must be done as differential (a and abar as inputs, q and qbar as outputs). This is where they get the power savings from--the swings are reduced and there's no path to power or ground to drain away charge. Without really discussing it, charge seems to just shift around on internal nodes between the differential logic states. They then use pure NMOS fets for logic, which removes all PMOS. The logic will never read the power rail, though--it will always be a Vt drop. I just looked this over quickly, but it seems the full-swing clocks and lack of PMOS make this work out fine.
For quick adoption, they'll need to work out clever techniques to connect this logic to standard clocked logic. Otherwise, it looks only a little bit easier to use than asynchronous logic. The issues they face seem very similar to asynchronous logic issues--tool support, interface to standard clocked logic, debug, test, etc.
It's not vapor.