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Three horse race

Will wireless front ends demand cmos amplifiers for cost efficiency over GaAs, or will SiGe take first place? By Philip Ling

According to Gartner Dataquest, we’re over the ‘peak of disillusionment’ for Bluetooth, which means most of the hype has hit the streets and it’s now time to get ready for real products. Hardly a day goes by without another company claiming to offer an ‘out of the box’ solution for creating a Bluetooth connection. The fact is, there will always be room for you, the engineer, to create the optimum solution for your application. While the solutions for the baseband are numerous, the alternatives for the front end fixtures are fewer, with farther between. This alone poses a dilemma and recognising that, where there’s a dilemma, there’s a business opportunity, there is now a spattering of power amplifiers being produced that have been designed specifically to meet the demands of a wireless link. The problem is, there is disagreement as to whether the amp should be cmos or bipolar based.

Cmos solution
The range of a Bluetooth transceiver is open to interpretation (the band allows for up to 100mW of transmit power), it is, of course, related to the amount of power pumped into the antenna.
It is here that the choice of power amplifier will prove critical. Yes, the software is important, but more so for differentiating the end product. For instance, in the case of Bluetooth, the protocol stack is well defined and available. Any product designed to operate as part of a wireless network will need to be certified, so choosing the right components, especially those that aren’t controlled by industry standards, could make the difference between getting the rubber stamp or going back to the drawing board.
Given that many of the devices operating in this way will be either portable or battery powered, efficiency is a high priority. For this reason, cmos would be the logical choice, but the war rages on over whether cmos can form the basis for an effective power amplifier.
One company which believes cmos is the way forward is Spirea (www.spirea.com), a Swedish fabless company which specialises in developing highly integrated, low power cmos radio devices for wireless networks. Spirea recently introduced a cmos power amplifier for 2.4 to 2.5GHz. BlueAmp, implemented in 0.18um, features a four level power control scheme to satisfy Bluetooth class 1 specification. Typical output power is 22dBm and it also sports on chip power down and intermediate matching. When used with its other cmos Bluetooth parts, Spirea believes it can hit the proposed glass price ceiling of including Bluetooth for less than $5.

GaAs guzzler
Others vehemently believe that cmos can’t meet the power efficiency of silicon germanium, and believe the latter technology will prevail over cmos power amplifiers, even though SiGe is inherently more expensive than cmos, it is still less expensive than existing power amplifiers developed for wireless transceivers based on Gallium Arsenide (GaAs).
This was backed up by two recent announcements; one from SiGe specialist, SiGe Semiconductor (www.sige.com), and another from Atmel.
SiGe Semiconductor became one of the first companies to spin out of the National Research Council of Canada. Described as a pioneer of the SiGe process, its product range revolves around rf building blocks and most recently it introduced the PA2423 family of class 1 power amplifiers. One member of the family has been integrated into Cambridge Silicon Radio’s BlueCore01. The same part has also been designed into Brain Boxes’ class 1 Bluetooth products. Specifically, it is in the BL-565 CompactFlash Bluetooth card and the BL-500 pcmcia card, said to be among the first consumer products to be fully compliant with the 1.1 specification.
Cypress Semiconductor announced in December that it has entered into an agreement with SiGe Semiconductor to collaborate on a SiGe process. Under the agreement, the companies will merge SiGe Semiconductor’s rf process and device modelling expertise with Cypress’ BiCmos and manufacturing capabilities. The companies expect to deliver production-ready SiGe processes during the first quarter of 2002.
“Developing a SiGe process internally strengthens our position in the communications markets, as the technology is uniquely capable of meeting the growing expectations of this market,” said Chris Seams, Cypress’s vice president, technology development and wafer manufacturing. “SiGe Semiconductor is an ideal partner, because their substantial experience in silicon germanium processes enables us to quickly and effectively bring the technology on line and provide superior performance products to our customers.”
Cypress confirmed that SiGe processes are gaining importance with wireless and broadband equipment, as the expectations for size, performance and power consumption exceed what can cost effectively be achieved in cmos. It enforces the belief that this technology dramatically reduces power consumption, to extend the battery life in handheld devices. Other benefits Cypress expects include improved phase noise to increase performance, data rates, transmission range, and stability over a broad temperature range; and more circuitry to be integrated on a single die, reducing the number of external components and associated board space.
"Cypress’ advanced manufacturing platforms and expertise in yield management provide the perfect complement to our standard SiGe processes," said Jim Derbyshire, president and ceo, SiGe Semiconductor. “We see a huge opportunity to build on this relationship, and hope to continue working with Cypress to extend the benefits of SiGe to new technologies and other markets.”

The third place?
Also recently, Atmel announced its own SiGe power amplifier for 2.4GHz, stating that it is ‘therefore much more cost effective than conventional GaAs power amplifier solutions’.
According to Atmel, the power amplifier is designed for 2.4GHz ism, Bluetooth (class 1), data, HomeRF, Dect, proprietary radios and Wlan applications. In Bluetooth systems, the device helps to boost the operation range beyond 100m.
It achieves an output power of +23dBm/ 3V at a gain of 25dB. A ramp up signal from a Bluetooth transceiver can even reduce the T7023’s gain to -17dB. As required by the Bluetooth specification, the ramp up signal also prevents an over swing of the output power by a defined, slow switch on. Due to the ramp control feature and a very low quiescent current, a switch transistor for the supply voltage is not required. This simplifies the design, saves external components, and so reduces production costs.
The device provides a power added efficiency value of up to 45% at 2.4GHz. Therefore, the current consumption is very low (165mA). Switching to standby mode helps to even further reduce the current consumption to less than 10uA. Also, due to the pae value, system costs are said to be lower than with conventional GaAs solutions, as fewer external components are required.
“Extremely high power efficiency and thus low current consumption and lower costs than GaAs solutions - these are the outstanding benefits that make our new product a milestone for advanced Bluetooth applications,” stated Udo Tillmann, marketing manager for the Bluetooth RF solution at Atmel Wireless & Microcontrollers Division. Samples of the T7023 in small MLP16 (4 x 4mm) packages are available now, and Atmel provides a design kit including reference design, design guide and RF board. Volume pricing is expected to be below $1 in quantities of 10,000.

Author
Vanessa Knivett

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