Analog Devices Inc. plans to introduce today a radio chipset that it calls the Holy Grail of radio receiver architectures.
Called Othello, the chipset features an open market Global System for Mobile communications direct-conversion receiver, which ADI said is a breakthrough in RF technology. The product meets current market demands, but is targeted for use in next-generation dual-band and triple-band GSM phones, said the company.
“People are used to having a small phone,” said Christian Kermarrec, product line director for ADI’s Cellular Terminal Solutions Group. Kermarrec noted traditional radio architectures would lead to bulkier multimode wireless handsets. “People won’t accept that their phone is now twice as big.”
ADI addresses that problem with its direct-conversion technology, also known as SuperHomodyne or zero-IF. The technology downconverts signals from RF to baseband in a single step, improving on the traditional SuperHeterodyne approach by eliminating the need for intermediate frequency devices used in traditional radio chipsets.
“All radios require a certain amount of filtering, as well as a means to convert the desired signal from RF to baseband where it can be processed digitally,” according to an ADI white paper on direct conversion. “Conventional SuperHeterodyne radios require many filters as well as several oscillators and frequency-conversion stages.
“These filters, oscillators and conversion stages add to the size and cost of the radio,” said the document. “As technology has advanced, conventional superhet radio size and cost has come down. Nevertheless, it has continued to be a major factor in GSM phone design.”
By eliminating the IF devices, SuperHomodyne requires fewer components, which leads to reduced manufacturing costs and smaller form factors, said ADI. The architecture provides savings of more than 30 percent in the total radio bill of materials and physical form factors for conventional radios, said the company.
Using Othello, a dual-band radio can be implemented in a total board area of less than 9 square centimeters with less than 90 components, compared with about 130 components in traditional radios, said the company.
In addition, the technology leads to increased standby times by requiring less circuitry and allowing the phone to “turn on” more quickly when in a resting mode, thus consuming less power. Standby times could reach 500 hours, said the company.
Othello represents the first GSM direct-conversion solution available to the open market, said ADI. Until now, the technology was proprietary.
Stan Bruederle, analyst at the Gartner Group, said direct conversion has been used in paging systems for at least a decade, but he noted paging receivers are much less complicated than cellular phones.
“As handsets continue to become more complex with multiband designs becoming the norm, any architecture that simplifies the product and reduces the power requirements will become very popular,” said Bruederle. “Direct conversion certainly qualifies as an architecture that satisfies these requirements.”
However, said Bruederle, “The proof of any solution is its use in volume production systems.”
ADI said it had to overcome several persistent implementation hurdles to develop direct conversion, including solving the interface between the power amplifier and voltage-controlled oscillator, isolation issues and large amounts of shielding.
Othello consists of two chips: the AD6523, which integrates the transceiver functions, and the AD6524 synthesizer. The product also includes companion software that allows radio calibration and dynamic direct current offset removal.
The company addresses transmission in the architecture with its virtual-IF transmit loop, which improves on the widely adopted GSM transmit modulation loop by eliminating a second oscillator and synthesizer as well as the high-loss bulky duplexer and external filtering found in older-generation phones, said the company.
The chipset is available to lead customers, with general sampling and full production scheduled to begin during the fourth quarter.
Siemens is one of ADI’s first customers for the architecture.
The company “recognizes this as a breakthrough technology which helps to save cost, power and space in future GSM handheld devices,” said Florian Seiche, director of business strategy at Siemens. “Siemens believes that advanced radio architectures such as this will substantially enhance future handset designs.”
In related news, ADI formed a new business unit focused on RF products. The company said it decided to form the new unit following an ongoing review of the company’s long-term strategic business opportunities. Kermarrec will head the unit.
