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Improved IMD Characteristics in L/S-Band GaAs FET Power Amplifiers by Lowering Drain Bias Circuit Impedance
Isao TAKENAKA Hidemasa TAKAHASHI Kazunori ASANO Kohji ISHIKURA Junko MORIKAWA Hiroaki TSUTSUI Masaaki KUZUHARA
IEICE TRANSACTIONS on Electronics
Publication Date: 1999/05/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Low Distortion Technology for Microwave Devices and Circuits)
AlGaAs/GaAs HFET, power amplifier, distortion, IM3, NPR, bias circuit, push-pull,
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This paper describes a high-power and low-distortion AlGaAs/GaAs HFET amplifier developed for digital cellular base station system. We proved experimentally that distortion characteristics such as IMD (Intermodulation Distortion) or NPR (Noise Power Ratio) are drastically degraded when the absolute value of the drain bias circuit impedance at low frequency are high. Based on the experimental results, we have designed the drain bias circuit not to influence the distortion characteristics. The developed amplifier employed two pairs of pre-matched GaAs chips mounted on a single package and the total output-power was combined in push-pull configuration with a microstrip balun circuit. The push-pull amplifier demonstrated state-of-the-art performance of 140 W output-power with 11.5 dB linear gain at 2.2 GHz. In addition, it exhibited extremely low distortion performance of less than 30 dBc at two-tone total output-power of 46 dBm. These results indicate that the design of the drain bias circuit is of great importance to achieve improved IMD characteristics while maintaining high power performance.