| Summary: | This paper presents a 50 MHz to 5 GHz broadband gain amplifier using a 0.5 μm gallium-arsenide pseudomorphic high-electron-mobility-transistor (GaAs pHEMT). For broadband design, a high gain cascode structure with a feedback network was used. To ensure the robustness of the design, the amplifier had to consider the effects of the Electrostatic Discharge (ESD)-protected diode and the package, which can degrade the broadband performance. Therefore, the equivalent circuit models of the package and the ESD-protected diode were analyzed and simulated in this paper. The designed broadband gain amplifier from 50 MHz to 5 GHz frequency band has a die size of 700 μm × 1000 μm and consumes 156 mW of dc power, and it was simulated with a gain of 18.7 dB to 20.6 dB, a P<sub>1</sub>dB of 15.3 to 16.9 dBm, and a OIP<sub>3</sub> of 26.5 to 31 dBm. Furthermore, the excellent gain flatness exhibited within 18.7 dB ± 1.92 dB at the interest of the frequency band.
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