This paper presents an X-band GaN HEMT power amplifier with a third harmonic-tuned\ncircuit for a higher power density per area and a higher power-added efficiency (PAE) using a\n0.25 �¼m GaN HEMT process of WIN semiconductors, Inc. The optimum load impedances at\nthe fundamental and third harmonic frequencies are extracted from load-pull simulations at the\ntransistorâ��s extrinsic plane, including the drain-source capacitance and the series drain inductance.\nThe third harmonic-tuned circuit is effectively integrated with the output matching circuit at the\nfundamental frequency, without complicating the whole output matching circuit. The input matching\ncircuit uses a lossy matching scheme, which allows a good return loss and a simple LC low-pass\ncircuit configuration. The fabricated power amplifier monolithic microwave integrated circuit (MMIC)\noccupies an area of 13.26 mm2, and shows a linear gain of 20 dB or more, a saturated output power of\n43.2~44.7 dBm, and a PAE of 35~37% at 8.5 to 10.5 GHz.
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