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Broadcom, Philips shrink Wi-Fi for embedded apps

Posted: 10 Sep 2003 ?? ?Print Version ?Bookmark and Share

Keywords:broadcom? philips semiconductors? atheros communications?

Eyeing Wi-Fi applications beyond the laptop, Broadcom Corp. and Philips Semiconductors will introduce chip solutions that support wireless connectivity in PDAs and portable consumer electronics. Success for either will depend largely on how well their solutions balance the criteria of power consumption, cost, footprint, and ease of integration.

Both offerings will also be compared with a fourth-generation two-chip 802.11a/b/g implementation, which Atheros Communications Inc. plans to announce next week. That chipset will feature an idle-mode power consumption of 4mW and novel signal-processing techniques that extend receiver sensitivity down to the cellular range of -105dBm.

WLAN chipsets typically have sensitivities in the -92dBm range, according to Craig Barratt, Atheros' CEO. At data rates of 11Mbps, for example, Broadcom specifies its sensitivity as -82dBm, while Philips has a figure of -84dBm. Broadcom also specifies a figure of -93dBm at 1Mbps.

"All the wireless-LAN stuff today is aimed at PCs, but this limits the market," said Mike Medina, director of technology and product planning at Broadcom. "People are now putting WLANs into things that one would never have thought would need wireless, but it's a fairly lengthy integration process from a hardware and software side. Plus, to embed WLANs, you need to reduce the form factor and power, as well as the overall bill of materials."

Broadcom's new BCM4317 single-chip 802.11b radio solution, called the OneChip, is built in the same 0.18?m CMOS process as the company's prior-generation WLAN chips. It integrates the company's BCM4301 802.11b baseband and MAC, BCM2051 front-end and an internally developed CMOS power amplifier (PA), plus diversity switches, bandpass switches, transmit/receive switches, and other components.

Medina said the OneChip requires just two external low-pass filters, and slashes the component count of a complete Wi-Fi miniPCI radio implementation from 200 to 30, while cutting standby power from 600mW to 6mW. "It costs just $10 for a full 802.11b module," he said. A complete 802.11b solution can be implemented on an SDIO card measuring 14.8-by-26.5mm, he added. OneChip is sampling now to select customers, with general availability in 2004.

For Philips Semiconductors, the single-chip concept is overrated. "We're well aware of the claims for single chip, but you need to look at the entire bill of materials and complexity of a well-behaved wireless system," said Paul Marino, VP and GM of the Business Line Connectivity Division of Philips.

Philips' two-piece solution comprises an RF front end built in the company's mature 0.5?m QuBIC 3 BiCMOS process and the SA2443 baseband/MAC built in 0.18?m CMOS. The RF portion takes a system-in-package route by putting the company's SA2405 transceiver with its SA2411 PA, along with the antenna switch and all required filters.

Philips' chipset enables a complete system to be built with just 26 components, takes up 300mm? (about 100mm? less than OneChip) and consumes 3mW in standby (half that of the OneChip), Marino said. However, at $12 each in 10,000 unit quantities, it costs $2 more than the OneChip, and won't be available until Q1 of 2004.

The power-handling capability of integrated CMOS PAs is generally suspect, but Medina, claiming an output of 13dBm, said the OneChip implementation compares favorably with competitors' versions in laptops. At that level, the chip burns 500mW, vs. 950mW in the previous implementation. "Laptop manufacturers say you have to be at 15dBm peak to sell a worldwide product. In reality, they lose 2 to 3 dB in the antenna subsystem, so they're really at 12dBm or 13dBm," Medina said. A handheld device has less than 0.5dB of antenna loss, because of its compactness and shorter routing distances, so the actual output at the antenna is similar to that of the laptop. "There's no difference in range," Medina said.

With the SA2411 PA, Philips' solution outputs 19.5dBm and consumes 821mW. However, because of the SiP design, the PA can be omitted and the designer can instead opt to use the SA2405 transceiver's on-board, lower-power PA. "This outputs 8dBm, but then the chipset only consumes 500mW," said Julie Tipton, WLAN product-line manager at Philips.

While a WLAN chipset typically takes a relatively small proportion of a laptop's battery power, the proportion rises rapidly in power-constrained handheld and portable consumer electronics devices, so both Broadcom and Philips said they paid particular attention to this parameter, and employed similar techniques.

"We focused on turning everything off whenever it wasn't being used," said Broadcom's Medina. The design employs techniques like gated clocking, and even determines the number of bits required to detect carriers. "While asleep we draw only 0.6mA, but we wake up every 100ms for 1.5ms to get the beacon [from the access point]. This burns 180mA, so our standby power amounts to 6mW," he said. Broadcom's previous implementation required 600mW in standby mode.

The core runs off 1.8V while the I/O and PA run off 3.3V. The OneChip's integration allows a component count reduction of 87 percent, Broadcom said. "This not only reduces the overall footprint, but also means less defects, faster test, less variability from build to build and higher reliability," said Medina.

Broadcom's demo SDIO board also includes the company's BCM2035 Bluetooth chip and utilizes still-unannounced proprietary techniques that allow the Bluetooth and WLAN devices to coexist. "We have an interface between the parts that we use to pass back and forth the receive/transmit timing, receive channel allocation and both packet- and profile-priority information," said Medina. "We make intelligent choices on a packet-by-packet basis to make sure there's no degradation apparent to the user."

Philips also has a coexistence solution in the works, but details are not yet available, Marino said.

Three reference platforms are available for the OneChip: the BCM4317CF (CompactFlash module), the BCM4317SD (SDIO module), and the BCM4317SDBT (SDIO with Bluetooth module).

- Patrick Mannion

EE Times

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