Texas Instruments Inc (TXN)

[Eric]

3G Chipsets: 3 Approaches to Apps-Processor and Modem Integration

>> There is More Than One Way to Design a 3G Handset

Alessandro Araldi
Worldwide OMAP™ Marketing Manager
Texas Instruments

http://tinyurl.com/96o45

Think carefully about the tradeoffs associated with each, since those tradeoffs can greatly affect your end goal.

One of the key decisions 3G-handset designer's face involves the degree of applications-processor and modem integration to best serve their marketing goals.

Currently, three distinct levels of system integration are readily available ...

... separate the applications processor and modem

... integrate the apps processor and modem into one IC.

... connect the modem to a separate multimedia accelerator.

The first approach, using a separate apps processor and modem, incorporates the two as discrete devices. Each device, available separately in the market, may include multiple processing cores. One processor, TI's OMAP™ device, depends on a RISC core, such as an ARM9 or ARM11 for high-interrupt command, control, and user interface functions, and a DSP for highly repetitive, math-intensive multimedia processing. Similarly, a modem may function most effectively with an ARM® processor running Layers 2 and 3 of the protocol stack while a DSP handles Layer 1.

The second approach, the processor and modem in one chip, typically incorporates multiple processing cores to perform the same work accomplished by two devices in a discrete configuration. In the OMAP device, different architectures address different market segments. For the smart-phone segment, an ARM processor, which might be complemented by dedicated hardware accelerators, manages the applications functions. A second ARM and a DSP handle the modem functions. For the cost-sensitive feature-rich segment, applications and modem functions share the same ARM core, while a DSP is dedicated to modem functions.

The third approach has a modem connected to a separate multimedia accelerator. This option is a variation of the first approach. However, it doesn't include an applications processor and therefore is not able to employ a high-level operating system. Instead, the modem manages essential command, control, and user interface functions, and a multimedia accelerator facilitates video, audio, and imaging.

Using a separate apps processor and modem provides flexibility, shortens time-to-market, and potentially increases performance. An existing modem in which the OEM has confidence and has made a significant investment can be reused and coupled with the latest apps processor, thereby leveraging past investments in the modem without compromising the processor's performance. This flexibility also means that, as is often desired in the marketplace, different suppliers can be chosen for each component. It also permits a processor running the same applications software environment to be coupled with different modems supporting different air interfaces such as GSM/GPRS, EDGE, WCDMA, UMTS, or CDMA. As a result, the OEM can efficiently develop a platform to serve multiple markets and operators with different modem technologies by changing only the modem while maintaining the same processor and software environment. Standalone products also give OEMs a choice of relatively low-cost modular options.

Many IC vendors tend to employ the latest semiconductor process technology for standalone microprocessors a year or more before they introduce integrated devices using the same geometry. One reason is that smaller geometries create power management challenges for modems that are easier to handle with standalone apps processors. It may take several months to address these problems in ways that permit integrated devices to deliver acceptable battery life. As long as process technology used for separate processors remains ahead of that used for integrated devices, performance on the separate processors will outstrip the performance achievable with higher levels of integration. Thus, the separate processor and modem approach permits quicker release of innovative technology into the marketplace, which can be important for OEMs and others seeking to differentiate themselves from their competition. A separate apps processor also can benefit from dedicated resources such as memory and bus, which would allow boosting performances especially in bandwidth-intensive applications like multimedia and gaming.

One of the key benefits of having the applications processor and modem integrated in one chip is resource sharing. The processor and modem share the same memory by leveraging the integration as well as a technology that effectively manages and prioritizes memory access. The processor and modem also share the same power management IC, whereas separate devices usually require dedicated power management chips. The integration of the two devices also tends to reduce the amount of logic required to connect the different functions at the system level.

Finally, employing an integrated device that includes complete hardware and software reference design, manufacturing-ready pcb schematics and layout, and integrated and validated telephony software can be (though is not necessarily) more cost-effective than developing and integrating hardware and software from scratch. In most cases, an integrated device requires less board area. That lets designers create wireless appliances with smaller form factors and free up board space for components that provide additional functionality.

An integrated device can simplify the overall phone hardware and software development due to its complete system solution. The chip set can be delivered with a complete hardware and software reference design. In that case, the reference design could be developed to pass the same tests that the actual phone must complete before being approved for commercial use. Because the integrated device usually is coupled with power management and RF in a chip set that's delivered with a pre-tested and pre-validated hardware and software reference design, overall system development time may drop.

From this point we start with the 3rd option. So this paragraph should be separated from the previous one. The benefits of having a modem connected to a separate multimedia accelerator include cost and flexibility. A multimedia accelerator generally is less expensive than an apps processor, since it's designed to perform only a subset of the functions of an apps processor. It's also less expensive at the system level, since it requires less memory.

As with separate apps processors and modems, this approach provides the flexibility to couple any modem with a given multimedia accelerator, thereby addressing multiple markets and operators with different modem technologies while maintaining the same multimedia environment. However, it clearly provides less flexibility in terms of software environment and applications it can support.

Alessandro Araldi is a senior marketing manager at Texas Instruments' Wireless Terminals Business Unit. This article was published in Portable Design in February 2005. <<

- Eric -