Novel Wideband Millimeter-Wave GaN Power Amplifier Design Using Transistors With Large Drain Capacitance and High Optimum Load Impedance

This brief presents a novel method to design wideband millimeter-wave (mm-wave) Power Amplifiers (PAs) under the scenario of high drain bias voltage and large drain capacitance. This technique uses a new and simple output matching circuit structure to compensate for the parasitic capacitance and control the $2^{\mathrm{ nd}}$ harmonic drain impedance, thus improving both PA bandwidth and efficiency performance. For verification, a Monolithic Microwave Integrated Circuit (MMIC) PA is designed using the proposed method in a 150 nm GaN-on-SiC process with a drain bias voltage of 28 V. The measurement results show that, although the Q-factor of the target drain impedance is as high as 4, the proposed PA can offer excellent large-signal performance with a saturated output power of 29.3-30.2 dBm and peak power-added efficiency (PAE) of 28.3 - 42.8% over a frequency range of 24.5-29 GHz, with a die size of $2.1\times1.3$ mm2. Meanwhile, when excited by a 200 MHz 64-QAM signal with a peak-to-average power ratio of 6.6 dB at 27.5 GHz, the amplifier can provide an average PAE of 23.6%, an error vector magnitude of 0.88/2.98%, and an adjacent channel leakage ratio of–50/–37 dBc (with/without applying digital pre-distortion), at an average output power of 22.8 dBm.