Analysis Nikkei Electronics Asia -- March 2008
Dissecting the "All-in-One" Mobile Phone

The latest mobile phones are brimming with features: 1seg reception, international roaming, high-speed datacom, GPS, and more. A glimpse inside a selection of handsets reveals distinct differences in design approach.

Autumn/winter 2007 mobile phone models offer more functions than ever before. Not only has one-segment programming reception become a common feature, but today's handsets also boast built-in High Speed Downlink Packet Access (HSDPA), international roaming such as Global System for Mobile Communication (GSM), and FeliCa electronic money. Many designs also have Bluetooth transceiver functions and Global Positioning Satellite (GPS) reception: in short, they're equipped with just about everything but the kitchen sink. Mobile phone manufacturers are aiming to increase market share by demonstrating to consumers how rich a selection of functions they offer. 

We took a look at how the insides of these multi-function handsets are designed. With the cooperation of a Japanese electronics manufacturer, we analyzed three representative multi-function mobile phones: the FOMA P905i VIERA mobile phone from Panasonic Mobile Communications Co Ltd of Japan, the au W53H Wooo mobile phone from Hitachi Ltd of Japan, and the Softbank 920SH AQUOS mobile phone from Sharp Corp of Japan.

1seg Viewing for 4hrs
The first thing we noticed after popping the cases open was that, in all three cases - despite the mass of new functions - the insides were laid out tidily. The neatly positioned components on the main circuit board of each model were especially intriguing.

The digital portion, including the application processor and baseband integrated circuit (IC), was cleanly separated from the analog portion with the radio frequency (RF) transceiver IC, power IC, etc, by the metal reinforcing frame. There was no evidence of hastily squeezed-in circuit blocks or haphazard jumpers across the main circuit board to implement the new functions. The overall feeling was that the design of third-generation (3G) mobile phones is close to complete. 

All three manufacturers apparently worked hard to slash handset power consumption, and as a result all three models deliver at least four hours of continuous viewing time for one-segment broadcast reception... and that's the drive time for standard Li-ion rechargeable batteries with 770mAh to 850mAh capacity. The first one-segment models only managed a little less than two hours using large-capacity Li-ion rechargeable batteries with 900mAh capacity or more.

Internal Antenna for 1seg
The three firms have taken different approaches to implementing one-segment reception, though. The P905i and 920SH have rod antennas mounted internally (Fig 1). The antenna can be extended to improve reception if required.

In the W53H, on the other hand, the antenna is completely internal: a miniature plastic antenna mounted on the main circuit board. There are still not very many models like the W53H without external antennas for one-segment reception, but they are likely to become the most common type. One source familiar with the industry predicts that in 2008 almost all manufacturers will switch over.

The one-segment reception tuner modules are all 7mm to 8mm square, at the cutting edge of ultra-miniaturization. The tuner module in the P905i is manufactured by Panasonic Electronic Devices Co Ltd of Japan, and the one in the 920SH by Sharp: both were either developed in-house or have come from a group company. The W53H uses a tuner module from Murata Manufacturing Co Ltd. Of the three, the Sharp module is the smallest, and appears to be a single-chip IC implementation of the receiver RF circuits and orthogonal frequency division multiplex (OFDM) demodulator.

Designers have approached case thickness differently, too. With the W53H and 920SH, thinness has been pursued as a goal unto itself, with minimum thicknesses of 14.2mm and 14.7mm, respectively, in their thinnest parts. The P905i, on the other hand, measures 18.5mm. To make up for the chunkier body, though, it offers functions including GPS receiver, Bluetooth, and a 5-Mpixel camera.

The P905i, from Panasonic Mobile Communications, is the first mobile phone to boast the VIERA name, after the flat-screen TV from Matsushita Electric Industrial Co Ltd of Japan, and is a prime example of the "do-everything" handset. The case has a unique open/close mechanism especially designed to facilitate one-segment program viewing, and is packed with functions including HSDPA high-speed datacom, 

GSM international roaming, a 480 x 854 pixel liquid crystal display (LCD) panel, and a complementary metal-oxide semiconductor (CMOS) camera with about 5.1 million effective pixels.

Open/Close Mechanism
One of the key features of the P905i is the "double-opening" mechanism, which opens not only in the vertical direction, like most mobile phones, but also horizontally. In addition to the standard hinge for vertical opening, there is also a single-axis hinge connecting the display and the keyboard vertically. Compared to the integrated dual-axis hinges more common in one-segment mobile phones, this design suffers from strength issues. 

A look at the mechanism from the back reveals that the single-axis hinge is secured to the top and bottom of the case with thick metal fittings (Fig 2a). The fittings are larger than the integrated dual-axis hinge. An engineer at a parts manufacturer pointed out, "It would be tough to thin out the display region with this structure. They must have been more worried about strength than thickness." To impart a feeling of rigidity when open, a magnet in the display side of the case catches a metal hook normally stored inside the keyboard side, providing 2-point support for the top and bottom case parts (Fig 2b).

Neat Component Layout
When the metal cover is removed from the P905i main board it can be seen that there are no seals for thermal radiation, electromagnetic interference (EMI) suppression or other purposes, and no jumpers or other quick wiring solutions. One engineer from a mobile phone manufacturer commented, "The design looks flawless, in spite of all the new functionality. They must have invested a lot of time in upstream design, such as repeated simulations for heat, noise and other characteristics."

The main board mounts the one-segment tuner module, application processor, RF circuits and baseband processor, among other things (Fig 3). In fact, it holds just about everything except the display. Semiconductors were integrated as much as possible to free up more main board real estate. The baseband processing IC is single-packaged into a package-on-package (PoP) with the application processor (based on Matsushita Electric Industrial's UniPhier digital household appliance platform) and memory from Samsung Electronics Co Ltd of Korea. RF transceiver circuits for wideband code division multiple access (W-CDMA) and GPS, power supply circuits and other components have also been integrated. Sub-boards are only used for slots for Subscriber Identity Module (SIM), microSD and other cards.

The W53H, from Hitachi, is the first to use the Wooo brand name used for the company's flat-screen TVs; its key selling point is the organic light emitting diode (OLED) display panel. The image quality of motion video in one-segment reception is obviously superior to that of LCD screens. The resolution, however, is only 240 x 400 pixels, roughly a quarter that of the 480 x 858 pixel LCD panels on the P905i, 920SH, and other handsets.

Samsung Logo on OLED
We removed the back panel from the display and had a look at the rear of the OLED panel (Fig 4). We wanted to see if there were any special design considerations for mounting it.

An engineer from a components manufacturer pointed out that other than the fact that there was no flexible printed circuit (FPC) for the backlight, the wiring around the logo (Samsung SDI Co Ltd of Korea, which manufactured the OLED panel) was pretty much the same as for an LCD panel. The only difference was a large number of capacitors and other components on the FPC connecting the printed circuit board to the OLED, probably to suppress EMI. The same components engineer added, "There are a lot more components than for an LCD panel. Maybe an OLED is more susceptible to EMI."

The OLED panel, including the case front side, weighs about 35g. The panel front appears to be high-strength glass, with a metal plate reinforcing it from the rear. The components engineer explained, "It's heavier than the standard type using an LCD panel. It looks like they gave some thought to improving strength around the panel."

Main Board Crammed
The main circuit board in the W53H, holding all the key ICs, is crammed with components on both sides (Fig 5). The sub-board is used for the microSD card slot, the LED flash for use in dim lighting, and a few other things. 

The dimensions of the main board are about 57 x 46mm, which is about the same size as the Li-ion rechargeable battery, at 38 x 38.5mm. The battery is about 6mm thick, which accounts for about 40% of the total thickness (thinnest point) of about 14.2mm. In other words, the battery and main board are next to each other under the keyboard, and the sub-board placed on top of the main circuit board. 

Many of the chips on the main board have silver seals on them, probably for EMI suppression. Another components engineer suspects that the chips must generate a fair amount of noise.

Pulling off one of the seals, we discovered the MSM6550 application processor from Qualcomm Inc of the US. This chip was developed in 2004 to compete with the CDMA2000 1x EV-DO, and is certainly not new. It seems reasonable to assume that the design of the circuitry is based on ICs that engineers were already familiar with, leaving them time to concentrate on the OLED panel, one-segment reception antenna and other features.

Along with the OLED panel, the other key feature of the W53H design is that the antenna for receiving one-segment broadcasting has been internalized, eliminating the rod antenna.

Antenna Structure
A look at the internal one-segment reception antenna reveals a unique structure that is actually made up of three antennas: a tunable antenna, a metal plate antenna and a board pattern antenna. Together the three of them pick up one-segment broadcasting. 

The engineer from the components manufacturer commented, "I don't know why they chose to use three antennas, but it is possible that there were problems with the reception sensitivity of the antenna components they chose."

"There are very few new components. It really looks like they just concentrated on making it all thinner," said an engineer from a components manufacturer who helped us dissect the brand new 920SH mobile phone with the AQUOS brand name from Sharp's LCD TV. This thinness is the outstanding characteristic of the 920SH, compared to prior models. The case is about 18mm at its thickest point, and only about 14.7mm at its thinnest. This is about 5mm thinner than the model's predecessor, the 912SH, at about 23mm. 

The 920SH is the 4th-generation AQUOS mobile phone for Softbank Corp of Japan. Changes from the 912SH model include international GSM roaming, and improvements to the LCD panel display performance, screen size, etc, but there are not many new functions. It looks as though component selection and other design issues were based on the predecessor handset, with designers concentrating on achieving a thinner result. The AQUOS mobile phone uses a cycloid hinge mechanism (Fig 6), with the display alone rotating 90 degrees and the keypad usable even while viewing one-segment programs. But the complex hinge tends to make the case thicker. The cycloid hinge in the 920SH is about 3mm thick, accounting for the majority of component thickness.

Thinner through Layout
Three techniques to achieve a thinner design were evident when we popped the cover: component layout on the main board, keyboard structure, and battery shape.

The top of the main board in the 920SH holds the parts for the majority of the mobile phone functions (excluding the display), like the RF circuits, baseband circuit and application processor (Fig 7). The RF and baseband circuits are implemented in a chipset manufactured by Ericsson of Sweden. An engineer at a components manufacturer was surprised to find an Ericsson chipset in a Japanese handset, commenting that it almost seemed to be made for export. As you might expect from a 4th-generation model, the board design was polished and the components were laid out neatly. The one-segment tuner module was the exception, though, being mounted on a sub-board. The components engineer speculated, "They probably ran out of mounting area on the main board when they added the GSM transceiver IC."

A closer look at the main board showed that all connectors, including those for the display, sub-board and camera module, are on top. All the components that might have some effect on case thickness have been mounted on the top of the main board in an effort to keep total thickness to the minimum. 

The connector for the fine coaxial cable connecting the display unit is only about 1mm high. A different components engineer said, "They probably used a low-height component so it would fit on the sub-board." The microSD card slot above the connector has a metal cover, probably for EMI.

by Hiroki Yomogita, Shinya Saeki

Websites:
Avago: www.avagotech.com
Ericsson: www.ericsson.com
Hitachi: www.hitachi.com
Matsushita: panasonic.co.jp/global
Murata: www.murata.com
PMC: panasonic.co.jp/pmc/company/en
Qualcomm: www.qualcomm.com
Samsung Electronics: www.samsung.com
Samsung SDI: www.samsungsdi.com
Seiko Epson: www.epson.co.jp/e
Sharp: www.sharp-world.com
Skyworks: www.skyworksinc.com
Softbank: www.softbank.co.jp/en
Spansion: www.spansion.com
STMicroelectronics: www.st.com

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