IEEC - Motorola StarTAC Cellular Phone

Motorola StarTAC Cellular Phone

The first cellular phones were semi-mobile car phones or transportable phones that came in a chic 'handbag' and weighed several pounds. Truly portable cellular phones became available in the mid 1980s, starting at a weight of about 850 grams.

Since then, cellular phones continuously have become smaller. Motorola has often lead the way with respect to smallest size and ultraportability, and its latest offering -- the StarTAC -- is the smallest phone ever. At 88 grams in a 5 cubic inch package, this phone is the size of a pager. In fact, Motorola calls it the 'ready to wear', 'wearable' phone that can be clipped to the belt like a pager, or worn around the neck like a jewelry accessory.

Design

The design of the phone is an extension of Motorola's typical flip phone; in this case the flip cover extends over the entire length of the phone. The phone also comes with a one-piece headset to allow hands-free operation.

A unique feature of the StarTAC is its ability to have two batteries attached at the same time. The flip cover supports either a slim (60 minutes talk time) or standard (90 minutes) lithium ion battery, while the base part of the phone can simultaneously support a second 'piggy-back' battery (90 minutes). Total possible talk time is thus 180 minutes.

It is interesting to note that Motorola chose to commit considerable effort to miniaturize an analog cellular phone. As described in earlier Prismark Partners bulletins (Personal Communications Services & Cellular Telephony - Understanding this Growth Market; Ericsson Digital Cellular Phone), outside the US the cellular infrastructure is rapidly adopting digital protocols. Digital systems can offer better transmission quality, enhanced service features, and more efficient use of the radio frequency spectrum. On the other hand, the US has a very well developed analog infrastructure, and is less densely populated than Asia or many European countries. Motorola believes that analog systems will continue to be popular in the US, while at the same time offering digital systems for international markets and the developing PCS market.

Description

The following is an abbreviated description of the construction of the Motorola StarTAC cellular phone. For a detailed discussion of these issues please contact the IEEC or Prismark Partners.

The StarTAC phone contains three printed circuit boards which are packaged in a tight 3D assembly and placed into the base portion of the phone. The weight of the StarTAC is almost evenly distributed between the housing, the three printed circuit boards, and the battery. The RF board alone accounts for 23.5 percent of the entire weight.

The main board provides the keypad on the top side and supports the logic circuitry on the bottom side. It is a four layer, thin glass epoxy construction measuring 1.875" x 1.750" with fine lines and many filled blind vias. The top side supports the keypad, the bottom has various SMT components.

The LED board is connected to the main board via a flexible circuit. It is a thin four-layer construction with very fine lines and four wirebonded LED driver chips. The entire LED module was manufactured in Singapore.

Bare Die on LED Board

The RF board contains all the RF circuitry, and is the largest board in the StarTAC, at 3.600" x 1.875". It is a thin, five-layer construction with fine geometries and blind vias. The thickness of the different layers, and the glass yarn content varies. The bottom side of the board contains three metal cans which provide EMI/RF shielding to numerous components mounted beneath them. In addition, CVD (chemical vapor deposition) coating of the inner surface of the back plastic housing provides EMI/RF shielding.

Conclusion

The Motorola StarTAC is the world's smallest cellular phone. It is setting the standard for future mainstream cellular phones. Can cellular phones get even smaller than the Motorola StarTAC?

The StarTAC is a clean design that was well executed during assembly. Without doubt, its size will be matched (or approached) by the competition, perhaps as early as the end of this year. Future phones will be even smaller. Where will this size reduction come from?

Silicon integration has tremendously increased the functionality per device, and the StarTAC's logic circuitry is implemented in just a few integrated circuits. Silicon integration will certainly continue, and the high volumes of cellular phones make integration of the highest order quite economical.

RF components have experienced extensive miniaturization over the past decade, but RF integration has lagged silicon integration. In the StarTAC, the assembled RF board accounts for almost a quarter of the total weight. Several vendors have introduced various few chip RF solutions, however, that will help to further shrink the RF side of wireless communications products.

The ratio of active to passive components is typically about 1:13 in the cellular phones we have torn down recently, and reached 1:34 in the Motorola Tango pager. Various approaches to integrate capacitors and resistors into the substrate exist, but have not yet been implemented. Interestingly, the Tango pager used mostly 0402 type passives, as well as some that were distinctly smaller. Further reductions in the size of resistors and capacitors can only be incremental, however, and will raise the costs of handling and assembly.

Finally, there is the question of the human-to-machine interface. The StarTAC already comes with a headset for hands-free operation. Without the LED and keypad, the StarTAC could probably have been implemented as a single board design. In fact, Inet has introduced a CDPD modem (which uses the cellular phone infrastructure) in a PCMCIA type III format, i.e. 54mm x 85.6mm x 10.5mm. In somewhat simplified terms, one can argue that the Inet Spider is missing only the interface to the human (and an internal battery) to be a cellular phone. Many companies are working on speech recognition, which may do away with the need for a keypad. Alternatively, an enlarged LCD may provide a virtual keypad, just as is already common on PDAs.

In essence, the electronics industry is moving ahead swiftly, and the convergence of computer, communications and consumer electronics technologies is exciting. What is needed are ideas and solutions for challenges like the ones cited above. If you believe you may have a solution -- be it at a systems, components, or materials level -- talk to a partner at Prismark Partners. We can help you identify the opportunities and options.

Copyright 1996 Integrated Electronics Engineering Center and Prismark Partners LLC.

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Warranty Disclaimer -- All information used in the preparation of this report was obtained from sources believed to be reliable at the time the information was collected. Prismark Partners LLC, its employees, its agents, and assignees have exercised their best efforts in preparing this report. Prismark Partners LLC extends no warranties with respect to this information and shall bear no liability whatsoever to the report recipient or to any other party as a result of the use of this report or the information contained herein.