Gateway to the future?

Direct conversion solutions expected to enable enhanced handset features

Once considered a theoretical pipe dream by the engineering community, direct conversion technology is now a reality, with chipsets being introduced this year that offer newfound promise throughout telecom - particularly in the wireless industry.

Through the use of zero intermediate frequency (ZIF) direct conversion, companies such as Qualcomm and Parker-Vision are expected to unveil chipsets during the next several months designed to rid handset makers of cumbersome intermediate frequency (IF) components without deteriorating signals.

If realized, this technology has far-reaching implications on future wireless handsets. Without IF components, the RF aspect of wireless phones requires less space, power and money.

"It's always been the Holy Grail for manufacturers," said Jim Tran, director of product management for Qualcomm CDMA Technologies, which recently announced its radioOne direct conversion chipset for CDMA phones.

Being able to devote more resources to enhanced features is sorely needed as handset providers and carriers strive to develop the next generation of wireless phones.

"They want to make the phones feature-rich... but they need more room in the handsets to stuff more things in there," Tran said. "This is going to be well-received because it is eliminating the IF parts... which definitely gives us more room on the board to play with."

Indeed, whether the subject is computers, CD-ROMs or wireless phones, headlines remind us almost daily of the miracles that can be achieved with digitized signals, as innovations refining them are developed with stunning regularity.

Yet the most valued signals - the human voice, for example - are inherently analog and must be digitized before being used in concert with modern technology. Despite this, the processes that transform analog signals into digital packets have remained relatively stagnant when compared with the breathtaking advances made with digital signals.

While improvements have been made in the size and speed of RF components, the basic superheterodyne architecture has remained largely unchanged. In this system, analog signals are processed through a series of IF components - most notably oscillators, amplifiers, demodulators and expensive surface acoustic wave (SAW) filters - and converted to a baseband mode, at which point the signal can be digitized (see figure).

Through direct conversion, this process is streamlined. The analog signal is immediately converted to baseband mode, forgoing the need for IF components, which occupy valuable space and use power in a handset.

"[Direct conversion] is the future of handsets... It will enable cheaper phones, smaller phones and battery life will be better," said Allen Nogee, senior analyst for Cahners In-Stat Group. "Today, you have a bunch of oscillators and SAW filters, and every bit of that consumes some power."

Indeed, Qualcomm officials believe radioOne will improve talk times in CDMA handsets by 20%. Combined with cdma2000 1X, the company believes the technology will enable standby times to increase about 400% compared with today's CDMA handsets.

All of which points to a bright future for direct conversion. "I really believe, in a few years, people are going to say, `Wow, everything has gone to direct conversion,'" said Jeffrey Parker, CEO of ParkerVision, which has patented its direct2data (D2D) direct conversion chip.

While referenced by many in the industry as an innovation, direct conversion has existed for some time, particularly in pagers and cordless phones. Various flavors of direct conversion are used in a handful of GSM handsets, but the expected cost savings have not been realized, Nogee said.

"Direct conversion has been around for a while," Nogee said. "Usually, the problems with it have cost more to solve than the savings gained by removing components."

However, many systems labeled as direct conversion today are not ZIF architectures. Although these allow IF components to be removed from the board, additional work still must be done in the baseband processor, which often is a proprietary solution that manufacturers want to avoid. Such enhanced baseband processors also diminish the cost and power savings that are the prime goals of direct conversion technology.

Still other direct conversion systems are ZIF architectures, but the baseband signal is not as clean as the signals generated from a superheterodyne system.

"The thing about direct conversion is there are some technical challenges at the system level that... create problems in terms of creating a clean signal," said Stan Bruederle, senior analyst for Dataquest. "Companies are applying various techniques to deal with these issues, and a lot of them don't like to talk about exactly what they're doing. My view is, with all these companies working on these solutions and addressing these issues, they'll eventually be put to bed, and we're going to see direct conversion receivers more common - it's just a question of time."

Qualcomm and ParkerVision believe the time is now. "[Others have] got the RF side of things; we've got a total solution," Tran said. In fact, Qualcomm is so confident in radioOne that the technology will be used exclusively in its chipsets beginning in 2002.

Still, past problems with direct conversion often lead to industry skepticism when the technology is discussed, Parker said. "There have been lots of direct conversion attempts in the past that... didn't quite integrate," Parker said. "So people's reaction to direct conversion has always been, `Sounds great,' but there's always been an excuse why you can't get all the way to the goal line.... We want to make sure nothing pops up that prevents you from getting to your goal line."

We've all heard the vision of what lies at the goal line: Eventually, everyone will carry hand-held wireless devices that will act as a phone, minicomputer and electronic wallet. These devices will allow users to perform tasks with ultimate flexibility and security, with no regard to the network being accessed or the mode used.

Considering the fact that the mobile phone industry will face a multitude of competing second and third generation technologies going forward, such all-in-one packages may seem far-fetched.

But officials for ParkerVision and Qualcomm say direct conversion technology is the foundation for building multimode phones - and that such handsets will require only one RF chipset, not the multiple paths that exist in today's multimode devices.

"In the future, there will be multiple 3G flavors, and we need to be able to work with each of them," Tran said. "We also need to be backward-compatible with 2G systems. Direct conversion is definitely needed to do all that and keep [handsets that retain] the same form factors."

While Qualcomm is focused on using direct conversion in CDMA phones, ParkerVision's goals for D2D also include uses in wireless LAN and Bluetooth applications. While many possibilities for the technology exist, Nogee believes the greatest benefit of direct conversion for wireless carriers is that it can help enable software-defined radios being used in handsets.

"Direct conversion enables you to put more of the radio in the digital domain and allows future enhancements such as making features changeable via software," Nogee said.

Reaching that stage is critical, because handsets with software-defined radios will allow carriers to differentiate themselves by customizing and upgrading feature sets without having to convince manufacturers to include the features in new handsets, Nogee said.

"Right now, it's too costly a process to add new features - and that's if you're a big carrier like Verizon and Cingular," Nogee said. "And if you're a small carrier, forget it."