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Wi-Fi/Bluetooth combos flood market

Posted: 02 Apr 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Wi-Fi/Bluetooth combo? WLAN standard? RF components? front-end analog radios?

Wireless chipmakers have unleashed a barrage of similar-sounding products for cellular handsets that offer simultaneous support for Bluetooth and WLANs. Broadcom Corp., CSR plc, NXP Semiconductors and Texas Instruments Inc. (TI) have each chosen a distinct path to overcome the challenges associated with integrating multiple RF components operating on overlapping frequencies.

Because Bluetooth and Wi-Fi (IEEE 802.11 WLAN standard) both operate in the 2.4GHz frequency range, they "struggle to be in the same band," said Will Strauss, president of market analysis firm Forward Concepts Inc. While they use different modulation techniques!OFMD in the case of Wi-Fi and FHSS for Bluetooth!"one can certainly interfere with the other if you are not careful," Strauss said.

Meanwhile, devices from Broadcom and TI, and a reference design from CSR add a third RF element for FM reception.

According to Arya Behzad, director of RF engineering for WLANs at Broadcom, the steady migration of process technology down to the 65nm node has enabled the integration of back-end digital circuits to support both protocols, but it has also posed challenges to the integration of front-end analog radios.

"We've had to follow the trend of the digital folks, and going to 65nm gave us tremendous gains in terms of performance and power consumption," Behzad said. "But it makes it all the more difficult to integrate an analog radio."

Robust calibration techniques are required to get reasonable performance and reasonable device yield when integrating a radio on-chip, he said. In the case of Broadcom's BCM4325 Wi-Fi/Bluetooth/FM transceiver, Behzad estimated that compensating for resistor variation in the process, for example, requires roughly 10 calibrations.

In the BCM4325, the three radios share the same master antenna, but are each supported by a separate frequency stabilizer, according to Behzad. Broadcom designers took measures to ensure that the voltage-controlled oscillators within the frequency stabilizers "did not pull on each other"!that they operate at sufficiently different frequencies and are not placed too close together, he said.

The techniques Broadcom pursued to make sure the PLLs operate at different frequencies included proprietary approaches that Behzad would not discuss. Brian Bedrosian, Broadcom's director of marketing for embedded WLAN, said the company uses precise filtering techniques to minimize bleed-through of the signals to a phone's cellular bands.

Draft-n support
For TI, whose WiLink 6.0 single-chip solution is the only one of the new products to support draft 802.11n of the WLAN standard, one of the main challenges was to comply with .11n's requirement for 2.4GHz and 5GHz operating frequencies, said Amir Faintuch, director of the company's wireless personal-area network and mobile-WLAN businesses. TI's WiLink 4.0, for example, can support 5GHz operation, but requires an additional front-end part to do so, he said.

"By definition, .11n requires a 5GHz band in any event," Faintuch said. "From a design standpoint, we try to make combining 2.4GHz and 5GHz capability in one part as smooth as possible."

The Wi-Fi/Bluetooth design challenge: These five factors influence integration in a cellular handset.

TI's approach involved simplifying the front-end of the device. Designers used an off-the-shelf power amp and included more functionality in the baseband chip. "Combining multiple radios in very small proximity on the same die is more challenging from an interface standpoint," Faintuch said.

But Martin Reynolds, managing VP and fellow at Gartner Inc., thinks TI and others may be setting themselves up for future hardship by packing more functionality into the baseband. "This is really just the beginning," he said. As more functions move to the baseband chipset, vendors will suffer because they will be selling fewer chips into handsets, he said.

QoS challenge
According to Carson Schimanke, product-marketing manager at NXP, the challenge of incorporating multiple radios into one handset is to prevent interference and ensure QoS. Unlike the other recent products, NXP's Nexperia 5210 is not a single-chip solution and does not incorporate an FM receiver.

"If you move around, you still need to make sure the service is OK. It's a really challenging use case," Schimanke said. "You need to have some blocking of the transmit path of the different radios. Also, how do you put the different radios physically in the handset?"

All four vendors claim that their products are power-thrifty!an important distinction for handset parts!although figures are hard to come by in some cases. Most say the migration to 65nm has helped keep the parts' power usage down. CSR quotes typical cellular power at 5mW when the phone is idle and 288mW for VoIP calls. TI says WiLink 6.0 consumes less than 50 percent of the power of previous WiLink generations. Broadcom says the BCM4325 delivers 40 percent lower idle power consumption than competitive solutions. NXP says the 5210 offers "industry-leading low-power performance."

Gartner's Reynolds attributed the surge of similar product announcements to handset makers' pushing vendors for the technology to support both protocols. "Some of these companies may have a harder time getting it out there than others," Reynolds said.

As with any new technology, he added, the first chips might not be perfect, but he expects the quality to improve quickly. "As long as the phone works, the Bluetooth and WLAN can be a bit patchy and people will not complain."

With vendors now integrating multiple radios into a single chip, the next step could be the integration of the cellular radio along with Bluetooth, Wi-Fi and FM. That would be a fundamentally more technically challenging undertaking, requiring the development of MEMS filters and other mechanisms.

'Next logical step'
Cellular-radio integration is "the next logical step," acknowledged John Jackson, a senior analyst at mobile-market research firm M:Metrics Inc., but "right now, it's a step ahead of the volume-market opportunity," since cellular operators have just recently warmed to the notion of including WLAN support in handsets. "It's not obvious that it's something that OEMs would rush to embrace, given the business environment that exists between the OEMs and the operators," he said.

Some question whether Wi-Fi attach rates will ever be high enough to justify integration of Wi-Fi, Bluetooth and cellular radios within the same chip. Jackson estimated that by around 2011, 16-20 percent of handsets shipped will have integrated WLAN. As with any technology, only a subset of the user base will actually leverage the capability, he added.

"A lot of market researchers say that by 2010, WLAN will be everywhere," Jackson said. "I tend to be a little more bearish."

- Dylan McGrath
EE Times

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