Scotts Valley, Calif. -- A 12-person company has disclosed a novel approach to semiconductor clocking that could slash power budgets and open the door to chips that clock at terahertz rates.

Startup MultiGig Inc. will deliver a handful of ambitious analog and mixed-signal products later this year using its Rotary Traveling Wave Oscillator clocking scheme. But the company faces multiple hurdles en route to its broader aim of replacing existing clock technology approaches used on most digital chips.

Rather than use traditional tank or ring oscillators and clock trees or grids, MultiGig (Scotts Valley, Calif.) es- sentially sends a pulse around differential transmission lines that are twisted back on themselves like a Mobius loop. The looped transmission lines are im- plemented in the metal interconnect layers on the chip and do not require any critical lithography or processing steps, so the manufacturing cost increase is kept to a minimum, ob- served Haris Basit, chief operating officer of MultiGig.

Paired back-to-back inverters sprinkled around the loop keep the pulse strength constant, like hands spinning a wheel. The length of the path defines the period. For example, for a 6-GHz rotary wave ring in 180-nanometer CMOS, the physical area for a ring is 0.35 mm².

"It's almost like a perpetual-motion machine; you start it up, and it keeps on going," said Stephan Ohr, analog analyst for Gartner Dataquest (San Jose, Calif.). The Rotating Wave technology consumes a small fraction of the power used by traditional clocking schemes, thus making it seem as if it sustains itself, Ohr said.

The technology holds the promise of slashing the dynamic power needed to drive a microprocessor's clock by up to 80 percent, according to MultiGig. Basit noted that a gigahertz-class, 1.2-volt CPU made in 130-nm technology can dissipate as much as 18 watts just on clocking functions.

On its first analog-to-digital converter, MultiGig will implement one physical ring with four phases. Taps can be implemented at any point around the ring to gain access to any of the four phases.

"We have done as many as 512 phase taps off a single clock, and they are very accurate," said Basit. "So we know we can get down to subpicosecond phases and effectively clock circuits at terahertz rates for use in very high-speed digital and mixed-signal products, such as A/D and D/A converters." The technology could drive next-generation serial I/O and radar systems, and it has attracted interest from the U.S. government for potential application in supercomputers, according to the company.

MultiGig has fabricated test chips in CMOS, bipolar and silicon-on-insulator processes and simulated devices in gallium arsenide, using foundries such as Jazz Semiconductor (Newport Beach, Calif.). "The fundamentals of this technology have been well-established and measured," said Basit, who has conducted and managed research projects at IBM Research, Bell Labs, Rockwell and the Defense Advanced Research Projects Agency.

Rewriting the rules
"This clocking technology lets you rethink how you design many circuits, providing a whole new rule book," Basit added. Yet the novelty also represents one of the hurdles of the approach.

"It's dazzling technology," said Ohr of Gartner Dataquest, and it could have a long-term impact on the clock market, which Gartner pegs at $1 billion a year and rising, particularly when extras like intellectual property and related tools are added to the mix. The question, Ohr said, is, "How do you implement it?

"This forces designers to do something different, and there is always resistance to that. You will have to force engineers to design this into their chips. That will take time to catch on"--at least a couple of years before the technique appears in digital silicon, Ohr estimated.

For example, while the rotary wave oscillator is expected to use no more silicon area than traditional clocks and may use less, it requires new thinking about chip layout. "It's like setting up a racetrack on the outer edge of a chip," said Ohr.

In digital applications, about 15 percent of each of the top two metal layers would be utilized by the MultiGig clock, but less wire could be used for the power distribution, said Basit. "We expect that for most digital applications, the area impact is neutral," he said.

And while applying the rotary wave technology to large digital circuits will require a significant redesign of the circuit architecture and physical layout to leverage all the benefits, some advantages can still be gained without extensive redesign. If the technology is dropped into an existing design, engineers can use the rotary clock to synchronize existing clock trees to reduce skew and latency. For designs with numerous repeated blocks, the phase taps can be used for each block to reduce power in the clock distribution approach.

Tool questions
Another stumbling block is a lack of EDA tools that could take advantage of MultiGig's ability to subdivide the clock for greater accuracy or throughput into hundreds, if not thousands, of phases. "Existing timing tools don't want to see a clock with more than two or three phases. They don't do a good job optimizing for the hundreds or thousands of phases we can deliver," Basit said.

MultiGig said it is working with a fabless chip maker that has a 90-nm test chip using the rotary wave clock in the works at Taiwan Semiconductor Manufacturing Co. One EDA company told MultiGig it could have modified timing tools in place in less than a year, once it sees the technology gain traction with chip makers. But this sets up a chicken-and-egg problem: Will the chip maker or EDA vendor commit first to create the market for the other?

"That's one of the consequences of doing something really different. Other people have to catch up with what you are offering," said Ohr.

"We started off thinking digital would be the biggest application area for us, and we still believe that," said MultiGig's Basit. "But there are a lot of hurdles."

Chip makers are already trying to absorb the concept of asynchronous logic as a way to lower power consumption by eliminating clocks altogether. Several startups, including Fulcrum Microsystems (Calabasas, Calif.), Handshake Solutions (San Jose) and Theseus Logic (Orlando, Fla.), are pursuing the approach, which Gartner predicts may take five to 10 years to gain traction.

Handshake says its asynchronous ARM996HS processor, when running full out, consumes one-third the power of a synchronous ARM968-ES. The part has the added advantage of consuming no active power whatsoever when not executing instructions.

Handshake claims its intellectual property, licensed to companies such as Boeing and Philips, already powers 25 different types of chips and is being used in more than 100 million devices, including electronic passports in Germany.

Analog action
MultiGig aims to get its technology in the market this year in analog products it will design and sell, including an 8- to 10-bit A/D that it says will sample at 1 Gsample/ second or more and will consume less than 450 mW. The part will find markets in high-end test gear, radar systems and basestations, and will top anything on the market by leaders such as Analog Devices, Basit claimed (see table).

"We are advancing the technology seven to 10 years just with our first products, which are not fully optimized," he said.

But the market for such A/Ds could be limited, said Ohr. Next-generation wireless basestations are looking for 12- to 14-bit resolution on A/Ds that only need to sample at about 250 Msamples/s, he added. "At a resolution of 8 to 10 bits, I see this more as a radar processor and less as a communications receiver," said Ohr.

The startup also aims to ship VCO-like integrated silicon timing devices. Targeting mobile phones, it is working with one chip maker to deliver a single voltage-controlled oscillator with multiple dividers that would handle four GSM bands and UMTS signals in a 180-nm CMOS chip requiring just 0.35 mm² of silicon. Unlike traditional designs, the MultiGig parts will shrink significantly as design rules shift to 130-, 90- and even 65-nm process rules, Basit said.

MultiGig has prototyped VCO-like devices for TV tuners and first-responder phones. It is also working on a universal frequency synthesizer. Such devices could create lower-cost approaches that would require fewer steps and filters to down-convert RF signals.

"This might be too expensive for the handset but could work well for basestations," helping to keep power levels down while providing stable and accurate VCOs, Ohr said.

As many as 150,000 basestations ship every year, typically using three to five radios each, said Will Strauss, principal of market watcher Forward Concepts (Tempe, Ariz.).

"It could be a lucrative market for them, if not a very big one. ASPs are very high," commented Strauss.

Beyond its own analog-device work, MultiGig is exploring what Basit described as "opportunistic" licensing arrangements with digital- and analog-chip companies.

-- Additional reporting by Dave Bursky