Designing a mobile handset? Don't miss the bus on cost savings

With these types of advancements, more applications and features are being squeezed onto the printed circuit board (PCB), which at the same time is shrinking in size. The reason for a shrinking PCB is quite obvious; customers want more features and functionality in smaller, more efficient packages. Faced with this type of challenge, product designers and manufactures must find new ways to minimize board space while integrating all of these devices.

To show how far handset design technology has come, and where it will go in the future, Figure 1 highlights the number of integrated circuits required in the typical mobile phone from early 2000 to what is anticipated in 2011. No question that the number of ICs will continue to increase.

Coming to the rescue, Philips established a new bus protocol better suited to interconnecting more complex hardware circuitry on shrinking PCB real estate. The new bus interconnect technology called, Inter-Integrated Circuits Bus (I2C), has since been widely embraced by the industry. Unglamorous as it may be, it is without question one of the technologies that has made portable devices the marvels they are today; delivering consumers products in sleek packages, with more features, and plug-and-play capabilities at lower per unit cost.

Designer and Manufacturer Concerns
Before the advantages of I2C can be thoroughly understood, it's best to review the specific challenges I2C solves. The technology in today's mobile handset is analogous to the technology found in today's automobiles: There are many components comprising the total system, and increasingly, the challenge has become how to efficiently interconnect those components. Thus, designers are looking for a better connection mechanism that would allow them to fit more peripheral devices in the same real estate area. And since so little room is available, minimizing the overall connection wiring on the PCB is a necessary requirement.

There are three major issues a mobile handset designer or manufacturer must address regardless of any one design. These issues include: product cost, shrinking PCB space, and incorporating more features with plug-and-play capabilities.

Product Cost
A variety of complex issues affect product cost. The price of the board can change depending on whether a single-layer or a multi-layer PCB design is used, as well as on the board's length and width dimensions. To keep the costs to a minimum, a smaller sized manufactured PCB with the fewest layers possible will ultimately cost less. By implementing I2C bus technology, which uses fewer lines, less space is required on the board, which in turn, reduces the overall cost.

Shrinking PCB Space
Shrinking PCB space is an inevitable trend in mobile phones and consumer electronics. Consumers want products that are easy to use, easy to carry, and easy to store. TV commercials today advertise how "thin" or how compact and easy to use one company's handset is over the other, even though each competitor adds the latest peripherals without expanding the overall size and space.

What's most impressive about looking at a mobile phone's PCB is the amount of technology crammed into the device with very little room for growth or expansion. Designers and manufactures are trying to save production costs and cut down on latency issues such as timing and distance from component to component, or circuit to circuit. As seen in Figure 2, space availability is low to nonexistent. In the 1990's a handset designer would never been able to achieve the same design density in such a confined space. Also, the peripheral components included in this design, would be unthinkable in a handset just ten years ago.

Looking at the cumbersome cell phones of the 1990's and comparing them to the size of mobile handsets today, one can appreciate just how much PCB space has shrunk in terms of overall size.

Increased Features with Plug-and-Play Capabilities
The number of features in today's devices has dramatically increased over those of the past. It is now common to see LCDs, card services, audio jack features and more in a mobile handset or consumer device. By having a type of plug-and-play device capability to easily integrate with similar designs, manufacturers and designers can easily change between model versions as they see fit to meet customer demands.

Here is an example how the I2C bus supports plug-and-play. Let's say a phone manufacturer sells a base handset "A" with standard LCD and audio components included. Later, he introduces an advanced model "B," which offers the same LCD and audio components as model "A" along with a multimedia card services component to bring in external files. The previous LCD and audio components were already learned features on the I2C bus before. Therefore, by plugging in a card services component into model "B," no overall system design has to change, except adding the card services connection. Thus, the system design introduced on model "A" can be ported to model "B" as is, without any changes. This facilitates application portability across product lines.