# Broadband Millimeter-Wave 5G Power Amplifier Design in 22 nm CMOS FD-SOI and 40 nm GaN HEMT
## 4 Discussion  
In the previous sections, three different PAs from two different technologies were presented. Typically, GaN is used for higher-power applications, but the designs in this work are all targeted to perform in the sub-Watt range. Small-signal measurements matched well with PEX simulations for both GaN #1 and the CMOS PA. However, large-signal measurement results did not match well for the CMOS PA, whereas large-signal measurements for the GaN #1 for \(V_{DD}\) = 6 V matched the simulation results rather well. Although measurements have not been taken on GaN #2 as this design is in the process of being fabricated, measurements on GaN #1 showed good agreement with EM simulations for \(V_{DD}\) = 6 V and thus will be compared to the other PAs here with \(V_{DD}\) = 6 V. Although the 22 nm FD-SOI CMOS PA used several power-performance improvement techniques (i.e., cascode and  
Figure 16: Measured ACLR+/ACLR- vs. carrier BW of the broadband CMOS FD-SOI PA at (a) 24 GHz and 28 GHz and (b) 37 GHz and 39 GHz. Figure 15: ACLR measurements of the broadband CMOS FD-SOI PA at 24 GHz using a 256-QAM-modulated 5G NR signal with PAPR = 8 dB at a signal BW of (**a**) 50 MHz, (**b**) 100 MHz, (**c**) 400 MHz, and (**d**) 9 \(\times\) 100 MHz. differential operation), the comparison of the three PAs in Figure 17 and Table 1 show that the \(P_{OUT,SAT}\) is significantly higher for the broadband single-ended or differential GaN PAs vs. the CMOS PA. This could be explained by the superior breakdown performance of GaN over the CMOS technologies, enabling larger output voltage swings per device. GaN #2 and the 22 FDX PA both used a differential topology and have similar gain, and the PAE as well as \(P_{OUT}\) appears superior for the GaN #2 PA vs. those of the CMOS-SOI PA. However, the broadband differential CMOS FD-SOI PA is much smaller than the GaN PAs in die size, with slightly higher power gain (but much lower \(P_{OUT,SAT}\) vs. GaN PAs), and it also includes an output balun, highlighting the excellent integrability of this CMOS technology. Using aggressive 256 QAM-modulated 5G NR input waveforms, great design insights can be gained from the measured ACLR vs. frequency on the signal BW vs. linearity and \(P_{OUT,Linear}\) for these two device technologies. When the signal BW is increased from 50 MHz to 900 MHz, the ACLR is degraded by \(\sim\)2 dBc for GaN #1 for both \(V_{DD}\) = 4 V and 6 V at 24 GHz and virtually does not degrade at 28, 37, and 39 GHz. However, for the CMOS PA, the ACLR degrades with this broadened signal BW by \(\sim\)4 dBc at all the carrier frequencies tested. Thus, this 40 nm GaN/SiC technology appears to have better linearity against very wide GHz 256 QAM-modulated 5G NR signals across the FR2 band, and offers significantly higher \(P_{OUT,Linear}\) and \(P_{OUT,SAT}\) than the 22 FDX CMOS technology. However, as we do not have measured \(P_{OUT,Linear}\) data for the differential GaN #2 yet, we could not ascertain if the superior \(P_{OUT,Linear}\) of broadband GaN PAs is mainly due to the device technology difference (i.e., GaN or FD-SOI), the cascode vs. common-source topology difference, the single-ended vs. differential topology difference, or something else (such as the output balun and/or matching details). Therefore, more detailed studies with additional measurement data are required to illuminate and clarify this important point in the future. Figure 17: Measurements of the broadband single-ended GaN and the broadband CMOS FD-SOI PAs and EM PEX simulations of the broadband differential GaN for (**a**) \(P_{OUT,SAT}\), (**b**) maximum PAE, and (**c**) \(S_{21}\) vs. frequency. Our GaN PAs are compared to other state-of-the-art medium-power broadband mm-Wave 5G PAs in Table 2, as well as against some GaN PAs in the literature with higher power values, as most available mm-Wave GaN PAs in the literature are targeted at higher-power applications without optimizing for high PA linearity.