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Moto Fone packs a punch of simple, elegant features

Posted: 27 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:iPhone? Motorola F3 Fone teardown? dual-band GSM phone?

For all the hoopla surrounding high-end mobile devices such as Apple's iPhone, the low end of the market can often tell an equally important story, at least in the engineering realm. Motorola's F3 Fone is one such entry-level example. Portelligent performed a teardown on the dual-band GSM phone shortly after its release to determine the level of innovation occurring in this segment.

Quietly launched in rural India initially, the F3 Fone is aimed mostly at first-time cell users in markets offering low-cost prepaid or monthly service. It's a bit unclear how far the Fone has migrated outside the original launch markets, but it can now be found in parts of Europe and Central/South America. A CDMA version has also been announced, but the original GSM variant is the focus here.

Sleek design
Before covering the technical aspects of the Fone, the first impressions from a consumer perspective are worth noting. We examine a lot of product!including low-cost devices!and quite often a declining price tag equates to a feel of declining product quality. Not so for the Fone, at least in my opinion. An innovative display, which we'll cover shortly, presents a unique look. A thin 9mm form-factor case provides a sense of style and elegance. Product stiffness and density transfer a feel of robust design.

I'll leave the software interface alone, other than to say simplicity has sacrificed a bit of what can effectively be done to promote easy access to settings and product usability. Still, the F3 delivers basic communications while still featuring downloadable ringtones and multilingual voice-help, which compensates in part for the lack of a rich menu-driven interface and printed instructions. Overall, the F3 walks the razor's edge separating inexpensive and just plain cheap, and Motorola deserves kudos for designing an up-market feel into an entry-level device.

Powered by DRP
So, on to the insides. The most notable story!for us, anyway!was the F3's use of semiconductor supplier Texas Instruments' LoCosto "single-chip phone." A quick look at the boards shows that this is a bit of a misnomer as other components (including integrated circuits) are still needed to implement a full system, but the chip breaks important new ground. The TCS2300 LoCosto device is a BGA packaged piece of silicon integrating two critical elements of the GSM platform!the digital baseband processor and the RF transceiver. No two-chip-per-package trickery is used here; rather, the whole point is monolithic integration of what are historically quite different chip technologies.

HTC X7500

The F3 Fone is aimed mostly at first-time cell users in markets.
(Click to view teardown.)

Looking at the die photograph, the TCS2300 can be seen to have two distinct regions. The leftmost part of the die contains the CMOS RF transceiver (perhaps 20 to 30 percent of the die by area) while the remaining area to the right contains the DSP, controller core and on-chip SRAM used to implement the baseband function. The RF section has been described by TI as being implemented with the company's Digital RF Processor (DRP) technology. DRP renders many of the traditional analog functions of filters, mixers and amplifiers into what are claimed to be more area-efficient implementations using switched-capacitor filters, oversampling converters, sampled-data processing and digital phase locked-loops. Not surprisingly, DSP is the final key element to going digital as close to the antenna as possible. The die view clearly shows spiral inductors and other traditional analog circuits, but the point remains that the radio has shrunk to a relatively small fraction of the die area.

DRP has been deployed by TI in its Bluetooth, Wi-Fi and GPS solutions, so the addition of cellular radios here rounds out a full-scale transition to a more monolithic communications world. The challenge in such an approach is to achieve economies in a mixed-signal integrated device. While the DSP core, SRAM and other purely digital elements all ride forward on the back of feature-size scaling, analog circuits on the same chip may not benefit as directly. Depending on how "digital" the DRP radio really is, the future scenario could be that the scaled digital pieces shrink to a small percentage of the die while analog content grows in proportion. In such a view, the leading-edge process technology applied at the wafer level delivers full scaling benefits only for an ever-smaller portion of each chip. Stated another way, the forward-looking challenge is mixed-signal monolithics that beat the cost structure of separately optimized digital, analog and RF circuits.

Of course, none of this is lost on TI, which has already announced digitally enhanced variations on the original LoCosto single-chip phone. The eCosto follow-up to the LoCosto chip adds processing horsepower and features in a similarly monolithic solution to prop up digital content and maintain an economic advantage by holding the line on analog proportions of the die area.

The TI architectures, including those seen in the Moto Fone, do split out the purest of analog, RF and storage functions in separate devices, however. The TWL3029 analog subsystem integrates power management and audio circuits in a second BGA-packaged chip. Similarly, a separate 2Mbyte NOR flash from STMicroelectronics (M58WL016) is used for code and user-data storage, and Skyworks' SKY77518 RF FEM provides RF power amplification and transmit/receive switching. The eCosto designs also have their own companion analog chip, RF PA and memory, suggesting that there continues to be a line drawn where monolithic solutions begin to break down.

Some see the mixed-signal SoC even more aggressively. While not a part of the Fone design, Infineon Technologies' new ULC2 platform extends the ULC1 platform (a functional parallel to LoCosto) to the endpoint of radio, baseband and analog subsystems on a single slice of silicon.

Smart display
Returning to the Fone, a second point of innovation is the electrophoretic display (EPD) supplied by E Ink and branded ClearVision by Motorola. Using tinted spheres whose black or white faces can be re-oriented to face the viewer based on an applied charge, the EPD is a high-contrast, bistable display. Once configured, the display microspheres require no further energy to hold their state, so on-screen images remain even after the battery is removed. This was a strange experience during the analysis!the device seemed to still be "alive" long after fatal blows of the knife had been delivered during the teardown process. While currently lacking the resolution, color and response speed of traditional LCD panels, EPD provides a functional interface for the basics of the Fone design.

The inset layered cutaway shows the EPD construction, using circuit-board-printed features as the driven electrode for the E Ink, with a top cover-film containing the blanket conductor (probably transparent indium-tin-oxide, or ITO). With the E Ink sandwiched between board and cover-film, an edge bead of glue around the top film seals the construction. We have no idea about the production yields Motorola may have achieved, but in principle the design is elegant in its simplicity. Two identical SSD1621 drivers from Solomon Systech provide the display's electronic interface, both wirebonded to and encapsulated in situ on the keypad/display PCB.

The business challenge for Motorola and others playing in the low-end segment is to assure that products like the Fone remain suitable, competitive offerings that are not so good that they impinge on the market for higher-end, higher-margin elements of the product portfolio. In the competitive handset space, this must be an incredibly tough balancing act to pull off.

- David Carey
President, Portelligent




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