A recent teardown report discussed a "pen phone" design from China's Haier Electronics (search www.eetimes.com for article ID: 18308615). The design was a surprisingly innovative example of handset form factor experimentation from a relative newcomer--enough of a surprise, perhaps, to spur the likes of Nokia to mount a fast response.

To wit, the Nokia 7280 appeared on the market as part of a series of "fashion phones" from the Finnish manufacturer. Whether the design launch was a coincidence or the result of competitive heat is impossible to tell, but the 7280 incorporates a number of firsts for the manufacturer.

Given the phone's lack of an alphanumeric keypad and its slide-open-to-answer stick design, some might mistake the slender Nokia 7280 for a spy widget. Measuring 115 x 32 x 19 mm in the closed position, the phone can be given a gentle tug to extend open to 125 mm in length for answering a call. Incorporating a VGA camera, the triband GSM phone also loads up on such features as Edge data capability, Bluetooth, FM radio, speakerphone, IR, voice recorder, polyphonic ring tones and an organizer with vibrator alerts.

The 65k color TFT display is protected by a half-silvered cover that doubles as a mirror when the backlights are off, suggesting a female-oriented target customer base. The phone's two-tone lacquer finish, art deco styling cues and cloth Nokia brand tag (like the tags on designer jeans) further amplify the notion of "fashion first."

In another snappy design twist, an LED is filtered through a lens to illuminate a ring surrounding the upper end cap of the phone. When the phone is in standby, the annular light pulsates with a sci-fi glow.

With so little surface area to work with, the user input was a challenge for Nokia designers. Rather than cram tiny keys into the design, Nokia used a rotating control pad--termed the NaviSpinner--surrounded by four conventional buttons.

Perhaps taking a cue from Apple's iPod, the wheel allows selection and entry of alphanumeric characters, although speed dials are difficult to pull off in the absence of prestored numbers. The rotary wheel differs from the capacitive-touch technology in the iPod, however, employing a mechanical set of brushes in a rotating switch: Spin the wheel, and the system counts contact openings and closures to detect input and direction. A center dome switch in the center of the scroll wheel arrangement allows entry or confirmation of input selections.

Small size means a small display. Nokia used a custom rectangular color LCD believed to be from Seiko Epson (now Sanyo Epson Displays). The 104 x 208-pixel panel is designed to be read in "landscape," with the phone turned sideways.

Miniaturization also affected the complexity of the electronics packaging and assembly. While the GSM chip set of the 7280 reflects tremendous progress in integration, the reedy physical envelope of the phone design still puts circuit board real estate at a premium. To save space, Nokia has employed both package stacking and chip stacking to go vertical and thereby minimize component footprint. The 7280's central baseband processor, the 4377083, is packaged in a plastic ball grid array that has an array of pads on its upper surface to accept a second package containing multiple stacked memory chips from Samsung, all servicing the memory needs of the baseband below.

The Samsung stacked memory consists of 64 Mbytes of OneNAND flash (KFD12162M), 16 Mbytes of mobile SDRAM (K4M28163LF) and 16 Mbytes of NOR flash (K8S28158TA), testament to the mix of volatile and nonvolatile storage needed in a modern cell phone.

The 4376371 analog ASIC, which rolls up A/D and D/A conversion plus audio and power management, is a Nokia custom design made by STMicroelectronics, as is the 4380079 GSM transceiver chip. Philips supplies an FM stereo radio in flip-chip form (the TEA5761). An STMicroelectronics/CSR chip is used for Bluetooth. ST also provides the VGA CMOS sensor module.

The imager itself is a pluggable module --you can see the receiving socket in the board photos--which enables Nokia to source an externally standardized camera solution, potentially from multiple vendors.

With all of these high-density array packages to mount in so little space, the circuit board technology is the next domino to fall in the complexity chain. The 7280 uses an advanced sequential eight-layer pc board from Ibiden, providing an arbitrarily stackable microvia structure. Very small vias can start and stop on any layer or be stacked to span multiple layers to provide routing densities far greater than drilled hole technology or even traditional additive circuit board techniques. Termed FVSS by Ibiden, the board technology and associated density come at an added cost.

Billed as a fashion phone more than a serious tool, the 7280 arguably hits the mark. With added function and capability over the Haier pen phone, the 7280 relies on a fresh approach to user input, new techniques for mechanical implementation and advanced packaging. The phone may prove unwieldy for power users wanting full keypad access; but for those with contacts on a SIM card, it is an elegant design for a night on the town.

Component Focus
Despite the ever-declining parts list needed to implement the cellular phone, handset designs continue to support an important market for passive components. With the need to control frequencies carefully throughout the RF signal chain, bandpass filters are critical here in the form of four surface acoustic wave filters from Murata Mfg. Co. Ltd. of Japan, which also supplies the 7280's transmit-receive switch module.

Frequency control is also important in generating the precise timing base used by the RF oscillators that set communications channel selection, and a temperature-controlled crystal oscillator from NDK Co. Ltd. (Japan) keeps the reference clock stable over variations in ambient temperature so calls do not end up drifting off-channel. Call quality is only as good as it sounds, of course, and here Nokia selected a #LTR711 earpiece from Sonion of Denmark to make the final critical link to the cell phone user's ear.

For a more complete parts list, go to click here.

David Carey is president of Portelligent (Austin, Texas), which produces teardown reports and related industry research on wireless, mobile and personal electronics (www.teardown.com).

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