In wireless digital communications, the integrated transceiver often fails to produce enough power to realize the full potential of a specification (typically +20 dBm). For a fully integrated CMOS radio on a single die, for example, output power seldom exceeds 0 dBm. In a white paper titled "RF Front-End Integrated Circuits," RFaxis, Inc. notes that the limitations of today's high-density radios have created a need for external amplifiers in various wireless systems. The note provides an overview of various front-end modules (FEMs) and their packaging options. It then spotlights the firm's own RF front-end integrated circuit (RFeIC), which houses a matching and switching network for transmit/receive operation as well as a highperformance linear power amplifier and low-noise amplifier (LNA) in a single BiCMOS die.
The firm points out that gallium arsenide (GaAs) is very suitable as a substrate for highfrequency circuits, as bulk GaAs has high resistivity. Yet MESFETs formed on this material require a dual voltage supply and associated bias circuitry, which increases size while reducing power efficiency. The note also explores the strengths and weaknesses of GaAs HEMTs, PHEMTs, and HBTs as well as composite GaAs (which will include indium-gallium-phosphide HBT and PHEMT devices on the same die). In addition, the document provides an overview of FEM design options including quadflat- no-leads (QFN), low-temperature co-firedceramic (LTCC), and flip-chip packaging. The second half of this note details the company's own design process, which allows the fabrication of all of the components needed for a FEM on a single die.
RFaxis, Inc., 36 Discovery, Suite 140, Irvine, Ca 92618; (949) 336-1360, FAX: (949) 336-1361, Internet: www.rfaxis.com.