Telefonini, la RF nel chip

Interessante questa corrispondenza di Electronics Times dalla conferenza ISSCC di San Francisco. I costruttori di componentistica per telefoni cellulari cercano il modo di ridurre all'osso i costi di fabbricazione dei telefonini, in modo da poter attaccare i mercati a bassissimo prezzo delle nazioni in via di sviluppo. La soluzione consiste nell'integrare il più possibile la radiofrequenza nei processori (ovviamente digitali) che elaborano la banda base. Uno degli ostacoli principali è il crosstalk, le reciproche interferenze tra le due a bordo dei minuscoli chip. Va da sé che a tali livelli di integrazione i dispositivi finali diventeranno ancora più flessibili e aperti a molteplici standard e modulazioni.

Engineers grapple with digital radio at ISSCC

Rick Merritt
(02/05/2008 4:50 PM EST)
URL: http://www.eetimes.com/showArticle.jhtml?articleID=206104558

SAN FRANCISCO, Calif. — Lowering cellphone costs by integrating radio components was a big theme for engineers at the International Solid-State Circuits Conference here Tuesday (Feb. 5). Several of the big cellphone chip makers came to ISSCC describing their current integrated digital RF devices, while others showed different techniques to eliminate external passive components.
Broadcom, Infineon and Texas Instruments described their latest devices for pulling more of the RF work into 2.5G digital devices, typically integrated with baseband processors. Separately Broadcom and the former cellular RF group of Analog Devoices Inc. (ADI), now owned by MediaTek (Hsinchu, Taiwan), described ways of eliminating passives from 3G phone designs.
These "very costly SoC developments" are motivated in part by the need to access huge new markets, said Bob Staszewski, a distinguished member of technical staff at TI.
"There is 100 percent saturation in mature markets such as Finland, Taiwan and Hong Kong, so continued growth depends on accessing emerging markets were you need something on the order of a $20 phone," Staszewski. "That requires integration to save costs," he added.
The TI engineer described a 90nm, 24mm-squared baseband with an integrated quad-band radio that TI is now shipping. The device still requires a 2W power amp, battery charger and SAW filters. Its integrated baseband includes a C54x DSP and ARM 7 running at 104 MHz.
"In the next few years the best we can do is bring into digital some RF and analog functions and integrate them with a baseband," said Staszewski.
Infineon went a step further. Its now-shipping chip includes a 250nm power management device integrated on a substrate with the 130nm baseband and digital radio on a system-in-package design. The baseband included a 260 MHz ARM and 178 MHz Teaklite DSP.
Engineers on both chips struggled with signal coupling and crosstalk issues. "Digital crosstalk effects are becoming more significant as the technology scales down, and digital noise will become increasingly significant," said Guiseppe Li Puma, a cellular RF system engineer at Infineon.
"You get a lot of signal coupling that is hard to predict and fix," said Staszewski.
"The more pressing design issue these days is removing external passives," said Tony Montalvo, a design center director for ADI who co-chaired the session on cellular transceivers.
"The big issue in WCDMA now is quad-band designs can require as many as seven SAW filters," he said. "These filters can dominate the board size and bill of materials costs of the phone," he added.
MediaTek described a tri-bandWCDMA/HSDPA transceiver that eliminated six SAW filers and three low-noise amplifiers. The device also reduces the cost of calibrating the radio to meet 3G standards.
For its part, Broadcom described a 65nm WCDMA transmitter using a feedback filter to suppress receiver noise while consuming just 65 mW. The design eliminated the need for a SAW filter.