Bye-bye, SiGe BiCMOS in cell phones, says TI

Silicon-germanium BiCMOS has been relegated to the status of a niche technology at Texas Instruments Inc., now that the Dallas-based company has demonstrated a single-chip CMOS concept for next-generation radio circuits used in cellular phones and other portable wireless applications. TI developers described details of the digital RF processor (DRP) architecture and 90nm CMOS process technology at the International Solid State Circuits Conference (ISSCC) last week in San Francisco.

TI aims to use its DRP architecture to ship samples of a new single-chip cell phone device for 2.5G GSM/GPRS handsets by the end of 2004. “CMOS processes can now be clocked at multiple-gigahertz rates. That was not true a few years ago,” explained Bill Krenik, TI’s advanced architecture manager for the wireless terminals business unit.

What’s more, TI has re-engineered the radio for production on 300mm wafers using CMOS, starting at the 90nm process node. Developers also have optimized the transistors for required noise performance levels and tweaked certain modules in the CMOS process. The DRP radio architecture reduces the number of analog functions — capacitors, resistors, and inductors — so that “we can build radios in CMOS with no additional mask adders,” Krenik said. “That allows us to integrate radios directly on the digital baseband parts and scale them aggressively to the 65nm and 45nm process nodes.” The move to all-CMOS single-chip cell phone devices reverses a previous trend toward silicon-germanium processes, which have been advocated by IBM, Atmel, Conexant, and others.

If TI were to build conventional on-chip radios in CMOS, it would take a half-dozen more reticle steps on top of the two dozen or so photomask layers normally used to make digital circuits, Krenik estimated. Up to 100 patents cover various aspects of TI’s DRP and related manufacturing technologies.

“Since we can put the radio in CMOS, we no longer have to support SiGe for these applications. As a component supplier, it takes one process technology off the list of those we need to develop for cellular [markets],” he added. TI currently plans to continue SiGe development for smaller-market applications, such as cellular base stations and high-performance analog functions. However, TI has turned to outside foundries for some of its SiGe devices, and it may increase outsourcing of those chips. “For wireless, we are definitely and decidedly moving away from silicon germanium,” Krenik proclaimed. — J. Robert Lineback, Senior Technical Editor


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