## 2 Principle of the CMUDPD Technique
### Comparison between Group A and Group B  
First, the differences between the simulation setup are shown in Table 2. For Group A, the bias voltage is constant and the supply voltage is varied. The operation modes are different, but they all belong to Class AB. For Group B, both bias voltage and supply voltage are varied, with more significant differences between the operating modes. By adjusting the bias voltage and supply voltage, the PA will operate in Class AB or Class  
Figure 9: Simulation results of PSDs with and without CMUPD. (**a**) Modes a1, a2, and a3 with and without CMUPD1. (**b**) Modes a1, a2, and a3 with and without CMUPD2. (**c**) Modes a1, a2, and a3 with and without CMUPD3. (**d**) Modes b1, b2, and b3 with and without CMUPD1. (**e**) Modes b1, b2, and b3 with and without CMUPD2. (**f**) Modes b1, b2, and b3 with and without CMUPD3.  
A. Then, the nonlinear characteristics of Class AB and A are shown in Figures 8 and 10. Figure 8a,b depicts the AM/AM curves and AM/PM curves of Class AB, respectively. Moreover, Figure 10a,b is the AM/AM curves and AM/PM curves of Class A, respectively. As can be seen from Figure 8b, the AM/PM curve shapes among modes a1, a2, and a3 are similar. Nevertheless, in Figure 10b, the AM/PM curves of Class A cross each other under a larger input power \(P_{\text{in}}\).  
It can be concluded from Figure 9b,e that the normalized PSDs with the CMUDPDs (a2 and b2 as feedback modes) can be suppressed by 13 dB on average. It can also be seen from Figure 11a-d that AM/AM and AM/PM with CMUDPDs become significantly convergent compared to those without CMUDPDs. Moreover, the results using an arbitrary mode as feedback to linearize other modes are summarized in Table 3. Other modes with CMUDPD, e.g., a1, a3, b1, and b3, can also achieve ACPR suppressions above 11 dB. For both Group A and Group B, the values of the error vector magnitudes (EVMs) with CMUDPD are reduced by one order of magnitude compared to those without CMUDPDs.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group A** & \begin{tabular}{c} **EVM** \\ **Simu./Expt.** \\ \end{tabular} & \begin{tabular}{c} **ACPR (dB)** \\ **Simu./Expt.** \\ \end{tabular} & \begin{tabular}{c} **Group B** \\ **Simu./Expt.** \\ \end{tabular} & \
\begin{tabular}{c} **EVM** \\ **Simu./Expt.** \\ \end{tabular} &
\begin{tabular}{c} **ACPR (dB)** \\ **Simu./Expt.** \\ \end{tabular} \\ \hline mode a1 W/O DPD & 5.20\%/5.90\% & \(-35.86/-38.52\) & mode b1 W/O DPD & 6.79\%/8.23\% & \(-32.90/-32.32\) \\ mode a2 W/O DPD & 5.21\%/6.04\% & \(-35.99/-38.53\) & mode b2 W/O DPD & 5.93\%/8.34\% & \(-34.15/-32.02\) \\ mode a3 W/O DPD & 5.31\%/7.18\% & \(-36.07/-38.23\) & mode b3 W/O DPD & 5.57\%/8.21\% & \(-34.97/-32.01\) \\ mode a1 W CMUDPD1 & 0.54\%/0.78\% & \(-49.13/-49.21\) & mode b1 W CMUDPD1 & 0.76\%/0.93\% & \(-47.28/-48.85\) \\ mode a2 W CMUDPD1 & 0.64\%/0.90\% & \(-49.12/-49.38\) & mode b2 W CMUDPD1 & 1.54\%/1.00\% & \(-45.59/-48.91\) \\ mode a3 W CMUDPD1 & 1.21\%/1.04\% & \(-46.58/-48.75\) & mode b3 W CMUDPD1 & 2.14\%/1.28\% & \(-43.67/-43.95\) \\ mode a1 W CMUDPD2 & 0.51\%/0.59\% & \(-49.13/-49.27\) & mode b1 W CMUDPD2 & 1.47\%/0.98\% & \(-45.91/-48.95\) \\ mode a2 W CMUDPD2 & 0.50\%/0.66\% & \(-49.44/-48.86\) & mode b2 W CMUDPD2 & 0.60\%/0.87\% & \(-48.08/-49.02\) \\ mode a3 W CMUDPD2 & 0.74\%/0.96\% & \(-48.21/-49.27\) & mode b3 W CMUDPD2 & 0.87\%/1.26\% & \(-47.05/-49.06\) \\ mode a1 W CMUDPD3 & 1.18\%/1.23\% & \(-46.42/-47.26\) & mode b1 W CMUDPD3 & 1.94\%/3.01\% & \(-43.39/-43.07\) \\ mode a2 W CMUDPD3 & 0.64\%/0.74\% & \(-49.84/-45.52\) & mode b2 W CMUDPD3 & 0.86\%/0.89\% & \(-47.56/-49.14\) \\ mode a3 W CMUDPD3 & 0.82\%/0.87\% & \(-49.74/-49.26\) & mode b3 W CMUDPD3 & 0.52\%/0.66\% & \(-48.54/-49.18\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: The simulation (simu.) and experimental (expt.) results of CMUDPD in Group A and Group B with each of the three modes as feedback modes.  
Figure 10: Nonlinear characteristics of Class A. (**a**) Gain curves versus input power for Class A. (**b**) AM/PM characteristic of Class A.