RF Design Magazine


Improved InGaP/GaAs HBT technology facilitates high linearity PAs
Oct 1, 2006 12:00 PM  By Nan-Lei Larry Wang

While innovative circuit techniques aid in improving the performance of high power amplifiers, underlying RF power transistors play an equally important role in achieving PA performance goals. This article reports on the improvement in a recently developed InGaP/GaAs HBT for 24 V to 28 V linear PA operation. Key improvements include adjacent-channel leakage ratio under WCDMA modulation, ruggedness to sustain high VSWR, and reliability. Plus, it reports on lifetime tests conducted to guarantee the performance of the improved HBT technology.

A 28 V solution

InGaP/GaAs HBTs were designed for the 28 V power application. The semiconductor device structure and microfabrication procedure were introduced. The 28 V process borrows many steps from its low-voltage counterpart. Power transistor design to the 10 W level was discussed. Special attention to the balance of the phase and magnitude of the RF signal across all the HBT fingers is essential to maintain the performance. High linearity in class AB and near-class B operation was achieved with the dynamic bias circuit approach.

The combination of the high linearity RF performance in the back-off power level, the ruggedness in RF power overdrive and the output mismatch condition, and the long lifetime demonstrated that InGaP/GaAs HBT technology is mature to serve the 28 V linear power operation in infrastructure applications.

Acknowledgment

The authors acknowledge the fruitful discussions with Walter Strifler and the technical assistance of Huy Pham and Sindolfo Gacayan. The effort by C. Dunnrowicz in the early phase of the project is appreciated.

References

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ABOUT THE AUTHOR

Nan-Lei Larry Wang received his BSEE from National Taiwan University, and MSEE and PhD from UC Berkeley. He has more than 20 years industry experience on RF, microwave, millimeter-wave IC and cellular phone RF transceiver design, which includes work at Raytheon Research Division, Rockwell International Science Center and Denso's cellular phone design center. He co-founded EiC Corp., which pioneered the development of high-reliability InGaP/GaAs HBT for wireless infrastructure base station and handset power amplifiers. In 2004, the business was merged into WJ Communications, where he is the vice president of Advanced Power Devices.

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