MANHASSET, N.Y. Two recent collaborations that focus on GSM and General Packet Radio Service (GPRS) handsets have brought into sharp relief the need to combine a programmable, scalable wireless device architecture with an optimized user interface.
The moves, which pair Texas Instruments with Microsoft and Analog Devices with Siemens, both seek to speed time-to-market and lower the cost of development for wireless equipment by maintaining compatibility from generation to generation to allow code and application reuse. The ADI-Siemens partnership goes a step further by marking progress toward validating direct-conversion receiver technology, with its associated space and cost savings.
Texas Instruments Inc. in Dallas unveiled an integrated GSM and GPRS solution for handsets and advanced portable devices that is optimized for Microsoft Corp.'s smart-phone platform. Code-named Stinger, the solution pairs TI's C54x-based baseband processor which has its own ARM RISC processor on board with a separate ARM9 applications processor to run Stinger applications.
Randy Ostler, marketing man-ager for TI's wireless computing unit, said the announcement is the result of work between TI and Microsoft that has been ongoing since the inception of the Stinger team. "Looking at the market, the key driver that will make wireless data useful and a significant driver in the industry is attracting a large number of third-party software developers to create interesting applications for the mobile and handheld form factor," Ostler said. "We TI and Microsoft had discussions and recognized that we had very similar visions of where we wanted to go."
The end result, Ostler said, "is that TI provides the chip set, while Microsoft has been able to provide a lot of advice on where they saw the human interface going."
For their part, Analog Devices Inc. in Norwood, Mass., and Siemens AG in Munich announced that Siemens has selected ADI's SoftFone DSP-based GSM baseband processor and the Othello direct-conversion RF chip set for Siemens' next generation of GSM phones and terminals. The phones are expected to emphasize extended battery life and to include GPRS wireless Internet access.
While underscoring the need for programmability and high performance as networks migrate to 2.5G and 3G, the announcement takes on increased significance in light of the advances Siemens has made in the handset business. According to Dataquest figures, Siemens was the fastest-growing GSM handset supplier in 1999 and is now jockeying with Ericsson for third place right behind Nokia and Motorola in terms of units shipped. Siemens executives said the company plans to maintain its aggressive approach by at least doubling its unit output each year, while increasing its appeal to a broader set of users.
This crucial stage of development for Siemens has made the choice to opt for ADI's direct-conversion Othello GSM chip set a significant engineering move, considering that the many vagaries of such designs still put them in the realm of black magic for many novices. According to Doug Grant, RF business director for ADI, the major obstacle remains self-detection (such as when the local oscillator leaks to the input of the low-noise amplifier), leading to dc offsets. Other issues include increased linearity demands on the LNA to prevent distortion, as well as the continuing debate over how best to partition filtering between the analog domain and the accompanying DSP.
But the payoff for a successful design is cost and space savings. "By removing the I/F stage, we save up to 30% in the cost and up to 40% in board space, mostly due to the reduction in filtering requirements and the accompanying SAW filters," Grant said.
Nonetheless, direct-conversion architectures have very few design wins, since the problems have made them automatically taboo to many designers.
"People are very skeptical about it, especially as GSM is a very exacting standard," Grant acknowledged, "so they Siemens were very intrigued about how we made it work. They looked at Othello, put it through its paces and liked what they saw. Considering the technical reputation of Siemens, they're the exact customer you want for your chip sets, because if there are any faults, they'll find them."
During the evaluation process for the Othello chip set, Siemens also decided to go with ADI's dc power management chips and its RF power-control chip.
Grant noted that the advantages of a direct-conversion design to Siemens will increase when multimode phones come into the picture, thanks in particular to the elimination of the SAW filters. Should this approach ever become an option, ADI has already conquered the wideband CDMA issues with a direct-conversion receiver for Mitsubishi earlier this year.
The Othello chip set debuted in late 1999 and is the first open-market direct-conversion RF chip set. The DSP-based SoftFone baseband processor is completely RAM-based, cutting development time and allowing its use in multiple applications.
The SoftFone comprises an ADI DSP, an ARM microcontroller, on-chip SRAM, a state machine for system timing and a bus arbitration system. Mixed-signal features include I/Q D/A and A/D converters as well as voiceband codec and system control converter options.
Combining Othello, SoftFone and the power-management logic, ADI said, yields a solution capable of 1,000 hours of standby time, while the reference design can be assembled on a circuit board half the size of a standard business card.
Of the deal with Siemens, Grant said, "For GSM, it's either us or TI. Second- and third-tier OEMs have generally liked us, as they like a standard product that they can tailor with their software. TI, however, has taken a more custom approach, which top-tier guys seem to like." Siemens' choice of Othello, Grant said, represents ADI's first foray into top-tier designs and says a lot about Siemens' vision. "What Siemens liked about our SoftFone is that they can use the same chip set across multiple phones and customize the phones," he said, "since everything's done in software and nothing's ROM-coded. They see their value as very much in the marketing side of the telephone, as long as the electronics still meet their standards."
TI is not standing still as ADI forays into the top tier. TI's Stinger-optimized chip set comprises four chips and will be fully compatible with its future DSP-based Open Multimedia Applications Platform (OMAP) products. According to the company, compatibility with future OMAP architectures will provide OEMs and applications developers with increasing levels of performance and battery efficiency, without their having to redesign existing software applications for new hardware architectures.
TI's integrated baseband and applications processor will be complemented by its integrated analog, power management and RF products. But the core will be the TWC2091, integrating the RISC processor and digital baseband. The chip set is sampling now, with volume production set for the second half of 2001.