Coexistence And Interference

Multi-radio coexistence is also critical to ensuring the best possible user experience for devices with Wi-Fi and Bluetooth. Since both technologies operate in the 2.4-GHz frequency band, concurrent transmissions can severely degrade performance and render both radios useless. Although Bluetooth uses an adaptive frequency-hopping (AFH) scheme to mitigate radio interference in the 2.4-GHz band, AFH is insufficient when there is little isolation between the Bluetooth and Wi-Fi radios—as is the case in a handheld device.

The coexistence problem is even worse when both radios are found on the same silicon die. To mitigate interference in close proximity, most chipmakers employ a standard three-wire coexistence interface between the Bluetooth and Wi-Fi chips. However, cutting-edge vendors have developed unique algorithms and hardware mechanisms that intelligently manage the 2.4-GHz band. This advanced approach is used to synchronize transmissions, avoid collisions, and find the clearest channel and time slot for Bluetooth and Wi-Fi operation. As a result, today’s combo chips can provide better performance than discrete solutions.

Component Size And Cost

As mobile designs get smaller and less expensive, the size and cost of every component is critical. Wireless combination chips not only are smaller than multiple standalone chips, they also require fewer external components to complete the system. For example, discrete Wi-Fi and Bluetooth systems typically require about 200 components, including power amplifiers, baluns, and low-noise amplifiers. Combo solutions can cut that number to 40 by sharing many of the redundant components between the Bluetooth and Wi-Fi systems and integrating others on-chip.

When you map these components to a board layout, the footprint of the discrete solutions is approximately 200 mm2 of board area, versus 75 mm2 for the combo chip. The smaller number of components also reduces the bill-of-material cost for manufacturers. One semiconductor supplier has integrated high-power CMOS power amplifiers into its combo chip, which eliminates the cost of an external power amplifier without sacrificing the system’s performance. Innovations like these will continue to make it more cost-effective for handset makers to add combo chips to multiple phone categories.

Antenna Placement

With multiple radio technologies come multiple antennas. In addition to one or more cellular antennas, today’s more advanced handsets must accommodate separate antennas for Bluetooth, Wi-Fi, FM, and GPS. This adds to the system cost and poses considerable challenges for board layout. Some combo chips can help to alleviate these challenges by sharing an antenna system between the Bluetooth and Wi-Fi radios.

Power Management

The more components on the board, the more power it consumes and the more heat it generates—all factors that impact battery life. Combo chips require fewer components, reducing overall power consumption. But even more important is the process technology that chipmakers use when designing combo chips. The leading vendors are using the 65-nm process node, which enables greater efficiency, tighter silicon integration, and lower power consumption. As a result, manufacturers can add Wi-Fi and Bluetooth to their devices without concerns over unacceptable battery life.

To further address the complex power requirements of mobile handsets and other portable devices, some combo chips integrate a power-management unit (PMU) to monitor usage patterns and optimize system operation to maximize battery life. For example, intelligent “sleep” and “wake” modes can power down components to minimize wasted power when not in use.

Some PMUs are offered with a complete set of software and device drivers to enable the integrated linear and switching regulator output voltages to be programmed, or for startup sequencing, providing a fast and efficient correlation between the power source and integrated components.

Summary

Driven by the functional consolidation in mobile devices, combo chips are the next big wave of semiconductor design. Such highly integrated solutions offer lower power, a smaller footprint, more cost-effective design options, and better performance than discrete wireless solutions, making them ideal for portable devices like mobile phones.

As these mobile devices become more media-centric, consumers will demand more connectivity features that enable them to access, enjoy, and share digital content among devices. To meet this demand, device manufacturers are looking to the leading chipmakers to provide combo solutions that reflect this new reality.