A GaN MMIC Load-Modulated Balanced Amplifier With Modified Output Coupler for Efficiency Enhancement Over a Larger Power Back-Off Range
Ziming Zhao, Xiao‐Wei Zhu, Jing Xia, Ruijia Liu, Peng Chen, Lei Zhang, Chao Yu, Wei Hong
Abstract
This brief firstly presents a monolithically microwave integrated circuit (MMIC) load-modulated balanced amplifier (LMBA) developed in 0.15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu {\mathrm{ m}}$ </tex-math></inline-formula> GaN process. In this brief, the asymmetric output coupler is applied for further enhancing output power and output back-off (OBO) efficiency over a larger OBO range. This MMIC LMBA operating mode is dependent on a three-ways active load modulation process by modifying the coupling coefficient of output coupler which can provide more design parameters and freedom. To validate the proposed LMBA at millimeter wave (mm-wave), a 24.7-25.7 GHz MMIC LMBA is demonstrated, fabricated and tested. Measurements show that this MMIC LMBA can deliver a 35.2-dBm saturated output power with a peak drain efficiency of 37.7%. At 6-dB/8-dB/10-dB OBO, 23.8-30%, 24.2-27% and 20-24% power added efficiencies (PAE) can be obtained, respectively. The measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> is 15-dB with a ±0.4-dB gain variation. When driven by a 100MHz 64-QAM OFDM modulation signal with a PAPR of 9.2-dB, the measured ACPR is improved to −45.04 dBc with DPD. In this case, the PA achieves an average efficiency of 25.2% and a 26.2-dBm average output power.