## 5 Conclusions  
This comprehensive review of state-of-the-art Doherty power amplifiers for 5G handset applications has highlighted the recent advancements in linearity enhancement, back-off efficiency improvement, and broadband operation. Key innovations, including dynamic power division, IM3 cancellation, parallel-plate couplers, and compact output combiners, have enabled DPAs to achieve superior performance in terms of efficiency, linearity, and bandwidth compared to conventional designs. Furthermore, the study comprehensively investigated how optimized chip layout design and flip-chip system-level packaging implementation affect thermal dissipation and overall device performance. The trade-offs between chip area, output power, operational bandwidth, and thermal management were quantitatively investigated to guide the development of highly integrated 5G handset front-end modules.  
The findings in this review provide a clear understanding of the current landscape and future directions in DPA technology for 5G NR applications. It is worth mentioning that, in addition to high Vcc operation using buck-boost DC-DC converters, low Vcc operation has been explored in the recent cellular system for low cost. This will make PA design  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Ref.** & **[10] 2021 IMS** & **[4] 2022 IMS** & **[21] 2023 TCSII** & **[3] 2024 IMS** \\ \hline \hline Supply Voltage (V) & 3.8 & 4.5 & 5 V & 3.4 V \\ \hline Frequency (GHz) & 3.35–4.15 & 2.8–3.8 & 3.3–4.2 & 3.35–4.15 \\ \hline \multirow{2}{*}{PA Process} & GaAs HBT & GaAs HBT & GaAs HBT M3 & GaAs HBT M2 \\  & (Flip-chip) & (Flip-chip) & (Bond-wire) & (Flip-chip) \\ \hline PA Die Area (mm\({}^{2}\)) & 1.1\(\times\)1.1 & 1.5\(\times\)1 & 1.34\(\times\)1.44 & 1.1\(\times\)1.3 \\ \hline Module Area (mm\({}^{2}\)) & 3.5\(\times\)2.5 \({}^{\star}\), Laminate & 2.1\(\times\)1.8, Laminate & 1.69\(\times\)3.85, Laminate & 1.3 \(\times\) 2.5, Laminate \\ \hline CW Past (dBm) & - & - & 36 & 33.4–34.8 \\ \hline CW PAE (\%) @Sat. & - & 32.2–47.3 & 39–44 & 38–43 \\ \hline CW Gain & 33–36 \({}^{\star}\) & 31.9–38.3 & 25.8–27.2 & 26.2–28.1 \\ \hline NR Pout (dBm) & 27.8 & 26–27.8 & 30 & 30–31 \\ \hline NR PAE (\%) & 35–42 & 22–30.6 & 26.2–30.3 & 31–34 \\ \hline NR ACPR (dBc) & –35 & \(-\)33 & \(-\)32.1 & \(-\)36 \\ \hline Using DPD & Yes & NO & NO & NO \\ \hline \multirow{2}{*}{Structure} & Single-end Doherty & Differential Doherty & Quadrature + single-differential Doherty & Wilkinson + differential Doherty \\ \hline \hline \end{tabular}  
*: Graphically estimated.  
\end{table}
Table 2: Comparison of the proposed PA with recently reported PA.  
more challenging. By addressing the critical challenges of linearity, back-off efficiency, and bandwidth, the DPA architectures presented here have demonstrated their potential to meet the stringent requirements of 5G handset PAs. The combination of advanced linearization techniques, efficient load modulation, and wideband impedance transformation has paved the way for highly integrated and energy-efficient 5G front-end solutions. As the 5G ecosystem continues to evolve, further research opportunities exist in exploring novel circuit topologies, device technologies, and system-level integration to push the boundaries of DPA performance. The review presented in this paper serves as a valuable resource for researchers, engineers, and industry professionals working on the development of cutting-edge linear 5G handset power amplifiers.  
Conceptualization, S.H. and H.C.; data correlation, S.H. and H.C.; writing--original draft preparation, S.H.; writing--review and editing, S.H. and H.C.; formal analysis, all authors; supervision, S.H. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The author wish to acknowledge helpful discussions with [PERSON].  
Authors [PERSON] and [PERSON] were employed by the company Beijing Onmicro Electronics Co., Ltd. The authors declare there is no conflict of interest for the manuscript.