Wi-Fi Radio Takes a Digital Turn

Intel's new transceiver pushes RF circuitry further into the digital realm, but will it make it out of the lab?

Are analog circuits on their way out? Granted, nature is analog and so, too, are the circuits that drive wireless communication. But analog devices are generally harder to miniaturize and have slowly been ceding ground to digital components. An experimental new radio chip developed by Intel could signal that the trend is accelerating.

The new radio, a Wi-Fi transceiver [pdf] that Intel says is constructed mostly of digital components, debuted in September at the company’s annual developer forum in San Francisco. Intel calls the technology a “Moore’s Law radio,” for its potential to take advantage of digital circuitry’s famed miniaturization trend. Ultimately, the technology could lead to smaller, slimmer portable devices, by integrating a smartphone’s radios and processors on a single sliver of silicon. But when that will happen and what sort of impact it will have on products is still unclear.

There’s good reason why this chipmaker’s fantasy of an essentially single-chip smartphone has yet to be realized. Radio-frequency circuits are especially sensitive to design changes, and the properties of analog components like inductors don’t improve as the devices get smaller. As a result, analog chips tend to lag behind their all-digital counterparts by a couple of manufacturing-process generations, which means that their features are much less fine.

Transforming analog radios—or at least some of their components—into digital radios could potentially bridge that gap. And over the years, digital circuits have taken over a bit more of the analog realm. The poster child for this trend is the phase-locked loop, a core signal-processing circuit that is now constructed from digital components.

To make its Wi-Fi transceiver, Intel says it had to go back to the basic mathematics of radio communications. “It’s not just a replacement of analog components,” says Yorgos Palaskas, who leads Intel’s radio integration lab. “It has to be done differently.” In the transmitter, for example, information that might otherwise be processed as RF signals is kept in the digital domain until the signal is amplified and goes out on the airwaves. Information on the intended amplitude of the signal is encoded in the timing of when the digital signal switches between 0 and 1.

Intel’s new Wi-Fi radio isn’t entirely digital yet, Palaskas notes. Some components are still analog. The design also isn’t optimized for area and consumes a little more power than a comparable analog transceiver might.

Moving Boundary:  To create its new digital Wi-Fi transceiver, Intel had to redesign core radio components that are traditionally made from analog circuits. Intels new transceiver is an approximate match of the digital radio schematic [bottom]; it still includes some analog-based filtering in the radios receiver.
Diagram: George Retseck
Moving Boundary: To create its new digital Wi-Fi transceiver, Intel had to redesign core radio components that are traditionally made from analog circuits. Intel’s new transceiver is an approximate match of the digital radio schematic [bottom]; it still includes some analog-based filtering in the radio’s receiver.
Click on image for a larger view.

“But the important point about the digital architecture is that it will scale moving forward,” Palaskas says. The radios “will get better and better with every single generation.” At Intel’s developer forum, he noted that a jump from a 90- to a 32-nanometer manufacturing process reduced one transceiver component—a frequency synthesizer—to a quarter of its size while cutting the power consumption from 50 milliwatts to 21 mW.

Intel made an impression when it presented details on core components of the radio at the IEEE International Solid-State Circuits Conference earlier this year. “There’s no question from a technical standpoint that they’re very novel,” says IEEE Fellow Robert Staszewski, an associate professor at the Delft University of Technology, in the Netherlands. Staszewski was previously chief technology officer of Texas Instruments’ Digital RF Processor Group, which developed digital radio components that could be integrated with basic cellphone processors.

Intel’s radio could potentially play well alongside the more advanced digital processors for today’s smartphones. The company previously demonstrated a chip codenamed Rosepoint, with two Atom cores and a Wi-Fi radio with more analog components than the one presented in September. But such integration might not be in the digital radio’s immediate future. Intel CTO Justin Rattner says the new radio technology may first emerge piecemeal in future radio chips.

Bringing processors with full digital radios to the market may have more to do with economics than technology. Initial development costs could be higher, and RF standards are less forgiving when it comes to inevitable variations in manufacturing, says Waleed Khalil, an assistant professor of electrical and computer engineering at Ohio State University. Digital processors that underperform can be set aside and sold for less. But with RF, if you have “a very small degradation in performance, nobody will buy your products,” Khalil says. Consumers may have to pay a considerable premium for more tightly integrated chips.

At the same time, analog radios are still very much in the running, says Mark Hung, a research director at Gartner. Although analog design takes longer, he says, so far chipmakers have “always been able to come up with new tricks to get it to scale.”

Still, Staszewski says Intel’s entrance into digital radio could very well inspire a change in the industry. Both analog and digital designers tend to stay firmly committed to their respective camps, he says, and so the industry has just been inching its way toward digitization. “I think Intel is the proverbial 800-pound gorilla,” he says. Sometimes when a giant starts doing something, he says, “then everybody will follow suit.”