October 2001

It's Time for Clockless Chips

Megahertz, shmegahertz. A few iconoclasts are building computer chips that dispense with the traditional clock. But they face big barriers in bringing their idea into the mainstream.

By Claire Tristram

"We're replacing dictatorship with anarchy!" Karl Fant tells me emphatically. Ponytailed and animated, the founder and chief technical officer of Theseus Logic fills the whiteboard with sweeping illustrative examples, kneeling down to use every bit of available writing space. He is in his socks. "Eventually every chip will be designed this way," he declares. "It's inevitable!"

Even in Silicon Valley, where company founders are known to indulge their nonconformist tendencies, Fant's Sunnyvale, CA, office comes as a surprise. His low desk is covered by a formless mass of memos and transcripts and other paper stuff, all mounding slightly toward the middle. There are no chairs-only pillows strewn artlessly about on the floor. If you happen to be me, you begin to regret wearing a dress and wonder where exactly you're meant to sit. But no: Fant leads you to a conventional conference room next door, where, thankfully, there is a chair. That's where he begins to evangelize about the coming revolution intended to wrest computer chips from the constraints of the past.

How? By throwing out the clock, the fundamental way that chips, since the dawn of the Computer Age, have organized and executed their work. Even those of us who know nothing about microprocessors know something about their clocks-Intel for years has used the clock speed of its microprocessors as a marketing tool, where faster is better. The number that dominates most computer ads, along with price, is a label like "1.3 GHz" (or gigahertz). That figure refers to the speed of the clock that governs the internal operation of the machine's microprocessor. Within every one-gigahertz microprocessor, for instance, there lies an oscillating crystal ticking one billion times a second. Engineers are trained to design chips where their first consideration is getting work done before the next clock-tick comes around. A chip without a clock would be about as useful as a page of text without any space between the letters. For most chip designers, throwing out the clock is difficult to imagine.

But not for Fant or his fellow iconoclasts working on clockless chips at startups, universities and corporate labs. It's a small group of ardent believers. Their annual conference attracts only a few hundred participants. Leaders in the field know one another well, and have one another's cell-phone numbers memorized. But while their methods and markets differ, they are united in their belief that clocked chips have run their course, and stand convinced that the advantages of their maverick approach, known alternatively as "asynchronous design" or "self-timed circuits," are so great that the chip industry will ultimately have no choice but to embrace it.

"Designers are realizing that distributing a clock across ever more complicated systems is becoming more and more difficult, and that sooner or later it won't work," says Alain Martin, a professor of computer science at Caltech, who built the first clockless microprocessor in 1989. He points out that as chips get more complex, more and more of the power it takes to run them gets eaten up by the clock itself, which now needs to coordinate the work of millions of transistors.

Dispensing with this overhead confers large advantages on asynchronous chips. One is vastly improved electrical efficiency, which leads directly to prolonged battery life. The clockless technology also yields an edge in computing speed. In labs at Sun Microsystems, Intel and IBM, clockless chips have increased the pace at which high-end processors do their work. In 1997, Intel developed an asynchronous, Pentium-compatible test chip that ran three times as fast, on half the power, as its synchronous equivalent.

At Theseus, Fant has focused on still another benefit of asynchronous design. Because these chips give off no regularly timed signal, the way clocked circuits do, they can perform encryption in a way that is harder to identify and to crack. Improved encryption makes asynchronous circuits an obvious choice for smart cards-the chip-endowed plastic cards beginning to be used for such security-sensitive applications as storage of medical records, electronic funds exchange and personal identification.

Are Fant, Martin and other clockless champions right? Frankly, yes. And yet despite the technology's clear advantages, clockless chips remain more theory than practice. The Intel device, for instance, never made it out of the lab. The failure of clockless chips to gain ground, in fact, makes them a perfect case study of a development with overwhelming promise that nevertheless faces huge obstacles to market introduction-even in an industry known for continuous and rapid innovation.