Electronic Design

Silicon Bipolar Amp Matches GaAs Performance

A recently developed high-performance bipolar RF power amplifier for mobile phone handsets retains silicon's cost, reliability, and flexibility advantages while offering gallium-arsenide (GaAs) performance for the 900-MHz to 1.9-GHz frequency range. Built from silicon, STMicroelectronics' new amplifier can hold on-chip bias and control circuitry for greater integration—functions that presently reside on a separate chip.

With a maximum operating frequency of 65 GHz and a breakdown of up to 5.0 V, the process has been refined to provide an optimum compromise between operating frequency and breakdown voltage, notes Guiseppe Ferla, R&D director of STMicroelectronics' Discrete and Standard Circuits Group in Catania, Italy. "Mobile phone manufacturers would no longer be forced to use GaAs technology, which is more expensive and much less suitable for integration in power amplifiers," he says.

This double-polysilicon, self-aligned process has worked up to 5 GHz. It can embed a variety of passives like resistors, metal-insulator-metal (MIM) capacitors and inductors, and active components. Plus, it exploits collector optimization and trench isolation to obtain high breakdown voltage and high-current-handling capability. Furthermore, trench isolation and an optimized die layout minimizes parasitic-capacitance effects. An innovative emitter-ground method enables maximum power gain.

STMicroelectronics built a demonstration 50-Ă™ input three-stage monolithic power amplifier with a 33.2-dBm output and 55% power-added efficiency (PAE) at 1.8 GHz and 3.4 VCC. Gain is about 33.2 dB (see the figure). The company plans to announce a commercial version next month.

For details, visit www.st.com.

TAGS: Mobile
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