SAN FRANCISCO — The interface between the antenna and silicon ICs in current wireless chips is complicated by the proliferation of standards. A panel at the International Solid Sate Circuits Conference examined potential solutions for integrating the interface onto an SoC.
"Filtering, switching and [the] interface to the antenna are commonly done using passive elements," said panel organizer Ali Hajimiri, professor at California institute of Technology (Pasadena, Calif.) "But the large number of passives required to interface to a multi-standard, single-chip radio increase the component count and size of the radio."
Added Aarno Parssinen of Nokia: "When the set of standards will be complemented with protocols like DVB-H, LTE or WiMAX, the number of frequency bands will be exhaustive. This has created one of the most challenging environments ever for electronics design."
Parssinen said the increased integration level for ASICs has spurred development, but most design challenges related to cost, complexity and interference are in the components between the antenna and silicon. Successful designs require a comprehensive approach including interference management and optimization of components at the product level.
"The versatile utilization of spectrum calls for a new set of technologies for enhancing front-end integration," he said.
Front-end components are being integrated into front- end modules (FEMs). According to Rich Ruby, director of technologies at Avago Technolgies, partitioning the front end has split into two paths: "by-band" and "by-technology" FEMs. By-band FEMS enable easy migration of phone platforms using different frequency bands. By-technology FEMS allow phone manufacturers greater access to optimized technologies.
"While CMOS makes inroads into the traditional markets owned by GaAs power amplifiers, it is not clear if or when CMOS can replace filters or, for that matter, resonators. In the meantime, pressure to improve performance, size and cost for both resonators and filters continue," said Ruby.
As low-cost CMOS continues to consolidate functionality from baseband to transceiver chips, GaAs power amplifiers and high-performance filters will continue to evolve in terms of power constraints, linearity and high rejection with low insertion loss, he added.
Meanwhile, Axiom Microdevices, with its distributed active transformer (DAT) technology has developed a 50 ohm matched power amplifier (PA) product in bulk CMOS without the use of a module technology, which is now shipping in high volume, claimed panelist Donald McClymont, vice president of marketing at Axiom. "CMOS provides the lowest cost path to product, assuming the technical hurdles of implementation can be crossed, of course," added McClymont. who thinks the possibility of further integration of the front end is hard but feasible.
"While integration of digital baseband and radio seemed impossible less than ten years ago, today large
systems-on-a-chips with the RF, mixed signal and digital blocks integrated on the same die are almost inevitable," said Broadcom's Hooman Darabi.
