Wireless Systems Design

Chip Propels Wi-Fi Beyond The PC Market

With Its Small Size, This Single-Chip Solution Opens The World Of Wi-Fi To Cell Phones, MP3 Players, And Other Handheld Devices.

Due to their popularity and continued miniaturization, Wi-Fi systems have become the technology of choice for Internet access. Now, Broadcom has raised the bar of lower power, higher performance, and smaller size. Recently, it announced a single-chip 802.11b wireless-LAN solution. The new AirForce One Chip BCM4317 transceiver system is about the size of a postage stamp (see figure). Yet it offers capabilities that are equivalent to any existing 802.11b chip set at greatly reduced power levels.

This solution combines all RF and digital 802.11b MAC/baseband elements on a single, CMOS-based silicon chip. Only a minimum of external components are needed to complete the BCM4317 transceiver system. This high level of integration makes the device one of the smallest wireless-LAN solutions available. When combined with the chip's low power consumption, this small size enables 802.11b capabilities to be added to a whole new set of compact mobile devices. Examples include digital cameras, MP3 players, cell phones, and handhelds. Previously, these devices were thought to reside in the exclusive domain of Bluetooth and IrDa technologies.

According to the company, the AirForce One board system is 87% smaller than other WLAN printed-circuit boards that boast equivalent capabilities. Measuring only 14.8 mm (0.58 in.) × 26.5 mm (1.04 in.), the AirForce One board is only slightly bigger than a U.S. dime. Yet it incorporates all necessary components except for the antenna filters, crystal, and 4 Kb of SPROM.

Inside the chip lies the RF front end. It includes the transmit/receive (T/R) switch, power amplifier, and Balun and matching components. The 2.4-GHz CMOS direct-conversion technology also is included. It bypasses the need for traditional IF designs. All of these RF subsystems are integrated with the digital system, which incorporates the 802.11b baseband, MAC, and encryption and buffer functionality. The result is a reduction in bill-of-material (BOM) costs that is estimated to be nearly 75% or roughly $5 per implementation.

This high level of integration reduces both the size and power consumption of the BCM4317. The architecture's power-management scheme also confronts the stringent power needs of small mobile devices. As stated by company spokesmen, AirForce One Chip designs consume 75% to 80% less power than other wireless LANs currently on the market.

This significant power reduction is derived from many factors. For example, the tight integration on a single chip helps to reduce host CPU utilization. Resources are therefore conserved for other embedded applications. The AirForce One Chip design also implements a SuperStandby mode. In this "deep-sleep" state, wireless activity is suspended for microseconds rather than being used continuously to look for incoming data. As a result, SuperStandby mode consumes less than 1 mW of power. Previous WLAN chip sets, which use traditional standby modes, consume more than 600 mW.

This solution also takes on the potential interference issues between 802.11b and Bluetooth. Broadcom has implemented a co-existence interface, which is designed to optimize performance between WLAN and Bluetooth radios in the same device. The MACs of the 802.11b and Bluetooth systems are constantly in communication. They exchange channel-allocation, packet-priority, and profile-priority information. This communication allows traffic coordination and prioritization according to the application type.

Three AirForce One reference designs are now being sampled: BCM94317SD, BCM94317CF, and BCM94317SB. Compared to traditional CardBus systems, these designs are 90% smaller and utilize 80% fewer components. The AirForce One BCM94317SD and BCM94317CF are production-ready modules. They should allow customers to integrate 802.11b connectivity into cellular phones, PDAs, digital cameras, and other small mobile devices. Using the BCM94317SB reference design, manufacturers also can add Bluetooth technology.

In addition to hardware, the AirForce One Chip solution includes the OneDriver software. This application suite provides a security portfolio that includes certified Wi-Fi Protected Access (WPA) and Cisco Compatible Extensions (CCX), as well as built-in hardware support for the Advanced Encryption Standard (AES). Also featured is the Xpress Technology software, which significantly improves the efficiency of a wireless network.

Broadcom Corp.
16215 Alton Parkway, P.O. Box 57013, Irvine, CA 92619-7013; (949) 450-8700; FAX: (949) 450-8710, www.broadcom.com.

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