Electronic Design

Silicon-Gernamiumn: Carbon HBTs Are Ready For Mainstream RF BiCMOS Processes

In cooperation with Frankfurt, Germany's High Performance Microelectronics, Motorola's DigitalDNA Laboratories in Tempe, Ariz., has successfully merged the silicon-germanium: carbon (SiGe:C) process module into mainstream RF biCMOS technology. As a result, conventional bipolars have been replaced with SiGe:C-based heterojunction bipolar transistors (HBTs). This was accomplished with an fT of 48 GHz and an fMAX of 86 GHz at a VCE of 2 V. The current drawn also is notably lower than that of the traditional SiGe transistors. Typical operating current is 500 µA.

This development will enable the melding of high-performance RF functions with dense, 0.35-µm CMOS circuits on the same RF chip. The process also lets Motorola integrate high-quality passives, including inductors. No more than 28 masking steps are needed to build an RF front end.

A dual-band cellular low-noise amplifier (LNA) is presently on the drawing board. With an input bandwidth of up to 2 GHz, the high-performance single-stage LAN will achieve a noise figure of less than 1.0 dB at a 16-dB gain. A three-stage version is under development as well. Other circuits aimed at multiband, multimode RF ICs are being developed using the SiGe:C-based biCMOS process. One circuit taking advantage of the new method, an RF front end for cellular transceivers, combines an LNA and a mixer on the same die.

Samples of the RF circuits are expected in the third quarter of this year. Production is planned for early 2001.

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