## 4 Implementation Results  
The trend toward monolithic integration in RF front-end designs is driven by the need for compact and cost-effective solutions in 5G handsets. By integrating the DPA with other RF components, such as filters, switches, and low-noise amplifiers, manufacturers can significantly reduce the size of the overall module. Monolithic microwave integrated circuit (MMIC) technology allows for the fabrication of multiple components on a single chip, reducing inner-connect losses and improving reliability. This integration not only minimizes the physical footprint, but also enhances performance by reducing parasitic inductances and capacitances that can degrade signal integrity. Figure 13 shows a recent photograph of the PA module [3]. The GaAs HBT PA chip, two CMOS controller chips, output transformer, and SMD components are mounted on a six-layer laminate substrate. The Doherty PA is fabricated in a GaAs HBT 2 \(\upmu\)m two-layer metal flip-chip process with a chip area of 1.1 mm by 1.3 mm. The PA chip with output-matching circuits occupies an area of 1.3 mm by 2.5 mm on the laminate. To verify the PA module, an evaluation board is fabricated using FR-4 printed circuit board (PCB). By carefully considering the integration and packaging aspects, designers can create highly efficient and compact DPA solutions that meet the stringent requirements of 5G systems. As shown in Figure 14, the PA module achieves a Psat of 34.8 dBm with 43% PAE at the N78 band. In the high frequency region of the N77 band, the PA module shows more than 33.4 dBm Psat with 38% PAE. The adjacent channel leakage ratio (ACLR) performance versus output power at different frequency bands is measured using a 5G NR-modulated FDD-DFTs-100 MHz-QPSK signal. Figure 15a shows that this [PERSON] PA module achieves about 31 dBm Pout with \(-36\) dBc ACLR at the N78 band from 3.3 to 3.75 GHz. As shown in Figure 15b, the maximum linear output power is about 30 dBm with \(-36\) dBc ACLR1 at 4.0 and 4.2 GHz at the N77 band, respectively. At the N78 band, the proposed [PERSON] PA module also supports 25 dBm output power, while the EVM is less than 2%. By optimizing \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \multicolumn{2}{c}{**Bond-Wire in GaAs**} & \multicolumn{1}{c}{**Flip-Chip in GaAs**} \\ \hline Advantages & 1. &
\begin{tabular}{c} Low cost and easy connection \\ No expensive gold layer, but normal copper bumps. \\ 2. \\ \end{tabular} \\
1. & Thermal resistance & All the inductors realized on laminate show better consistency. \\
2. & The GaAs substrate should be thinner better heat dissipation. But to be thinner, it will be more fragile. & 3.
\begin{tabular}{c} Low thermal resistance \\ Strong ground connection through numerous solid \\ copper pillars. \\ \end{tabular} \\
2. &
\begin{tabular}{c} Low parasitic inductance \\ Easy to achieve high performance. \\ \end{tabular} \\ \hline Disadvantages & 1. & High cost and high complexity \\ Golden bond wires connect with components on the laminate substrate through golden pads. & 1. & Limited thermal cycling reliability \\
2. & Bad consistency of bond wires & Flip-chip interconnects experience high thermal stress due to coefficient of thermal expansion (CTE) mismatch between the chip and substrate, potentially leading to solder joint fatigue failures. \\ \end{tabular} \\ \hline Disadvantages & 2. &
\begin{tabular}{c} Bad consistency of bond wires \\ The variation of height of bond wires may result in deviation of performance in massive production. \\ \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of the bond-wire and flip-chip technologies. authors' knowledge, this is the first broadband Doherty power amplifier for 5G NR handset applications with a low supply voltage of 3.4 V. The improvements in PAE, ACLR, and bandwidth demonstrate the effectiveness of the key innovations discussed in the previous sections. The PAE at 6 dB PBO increased by 5% to 10%, indicating a significant enhancement in back-off efficiency.