In this work, we propose a compact CMOS power amplifier using a differentially coupled series inductor for motion detection radar applications. The proposed switching-mode power amplifier is designed with a cascode and differential structure. To realize a compact size matching network, a differentially coupled series inductor is used in the input matching network. In the proposed power amplifier, two typical spiral series inductors for the input matching network are replaced with a single differentially coupled series inductor. As a result, the used chip area of the differentially coupled series inductor is smaller than half that of a typical inductor for the given inductances of each inductor. Additionally, to obtain a high gain characteristic, we adapt modified mode-locking techniques for the power stage of the power amplifier. To verify the feasibility of the power amplifier, we design a 9.5-GHz power amplifier with a 130-nm RFCMOS process. We obtain saturation power of 15 dBm while the power-added efficiency is approximately 28%.
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