A Linear and Wideband GaN MMIC Distributed Efficient Power Amplifier Design Using Unequal Power Splitting and Bandpass Unit Network

This article proposes a new GaN wideband and high-linearity distributed efficient power amplifier (DEPA) for millimeter-wave (mm-wave) applications. It starts with an in-depth analysis of the nonlinearity effects in the DEPA, which identifies two theoretical findings: 1) the gain expansion feature of the DEPA output network and 2) the dependence of the DEPA input network nonlinearity on the power splitting ratio (PSR). These outcomes reveal the feasibility of manipulating the DEPA input and output network nonlinearity to compensate for gain compression of the real transistor, thereby improving the overall DEPA linearity. Using this method, a wideband and high-linearity DEPA is designed in a 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 $ </tex-math></inline-formula>m GaN-on-SiC process. In the design, a bandpass T-structure-based distributed unit network is developed to replace the traditional capacitive-loaded TL one to realize broadband matching at back-off power and wideband traveling-wave operation of subamplifiers at saturation. This consequently allows the DEPA to support dual operation modes: the high back-off efficiency mode and the enhanced-bandwidth mode. Continuous-wave (CW) measurements reveal that in the former mode, the DEPA is capable of delivering saturation output power (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {SAT}}$ </tex-math></inline-formula>) of 36.4–37.6 dBm and gain of 15.8–18 dB, with excellent power added efficiency (PAE) of 21.5%–30.2%, 24.5%–31.1%, and 32.1%–38.7% at output power (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {OUT}}$ </tex-math></inline-formula>), that is, 7.5-, 6-, and 0-dB back-off from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {SAT}}$ </tex-math></inline-formula>, respectively, while maintaining good gain flatness with fluctuation minimized for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {OUT}} \lt 33$ </tex-math></inline-formula> dBm, over 24–29 GHz. In the latter mode, the proposed DEPA can provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text {SAT}}$ </tex-math></inline-formula> of 35.8–37.1 dBm, a saturation PAE of 31.6%–38.9%, and a higher gain of 18.5–20.5 dB over a broader frequency range of 24–30.5 GHz. In addition, when operated in the high back-off efficiency/enhanced-BW mode and excited by a 400-MHz 5G NR 64QAM signal with a peak-to-average ratio of 9.65 dB, the DEPA can deliver average PAE of 20.4–28.8/16.9%–19.8% in the range of 24.25–29/29–30.3 GHz and maintain good error vector magnitude of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lt -25$ </tex-math></inline-formula> dB, without using any digital predistortion (DPD).