## 3 Results
At LO\({}_{\text{in}}\) of 0 dBm, the mixer achieves a measured/simulated CG of 15.6/15.7 dBm, close to those (16.6/16.2 dBm) at LO\({}_{\text{in}}\) of 4 dBm. This indicates that LO\({}_{\text{in}}\) of 0 dBm is a reasonable choice for the switch operation of the LO switch transistors. Figure 8: Measured and simulated (**a**) LO–RF and LO–IF isolation versus LO frequency, and (**b**) CG versus LO input power characteristics of the mixer. Figure 7: Measured and simulated (**a**) S\({}_{11}\), and (**b**) S\({}_{33}\) of the mixer. The on-wafer NF measurement was performed using an Agilent N8975A noise figure analyzer (0.01-26.5 GHz). An Agilent 1-50 GHz noise source with a 7-20 dB excess noise ratio (ENR) is used at the RF input. The LO input signal is provided by an Agilent E8257D signal generator (up to 67 GHz). Figure 9a shows the measured and simulated CG and NF versus RF frequency characteristics of the mixer. IF frequency is fixed at 0.1 GHz. The mixer achieves a measured CG of 15.6 dB at 28 GHz and CG of 14.4 \(\pm\) 1.5 dB for 12.4-32 GHz, corresponding to an f3 dB of 19.6 GHz. The result is close to the simulated CG (15.7 dB at 28 GHz and 14.3 \(\pm\) 1.5 dB for 14.3-32.5 GHz, corresponding to an f3 dB of 18.2 GHz). The broadband CG of the mixer is attributed to the wideband RF- and LO-port Zn matching (5\({}_{11}\) and S\({}_{22}\)) and near perfect wideband-coupling of the \(\lambda\)/4-TL-C-based coupler. Moreover, the mixer achieves a measured NF of 7.6 dB at 28 GHz and 7-9.7 dB for 12.4-32 GHz, close to the simulated NF (6.7 dB at 28 GHz and 6.2-9.3 dB for 12.4-33 GHz). Figure 9b shows the measured and simulated CG and NF versus IF frequency characteristics of the mixer. The mixer achieves a measured CG of 15.6-12.6 dB for 0.1-1.9 GHz. The 3 dB IF bandwidth (f3 dB,IF) is 1.9 GHz, wider than the required 1.5 GHz for 5G NR band N257 (28 \(\pm\) 1.5 GHz) application. The result is close to the simulated one (15.7-12.7 dB for 0.1-2.2 GHz, i.e., f3 dB,IF of 2.2 GHz). The mixer achieves a measured NF of 7.6-8.1 dB for 0.1-1.9 GHz, close to the simulated one (7.7-8.3 dB for 0.1-2.2 GHz). Furthermore, the mixer achieves a decent P1 dB and IIP3 of \(-\)10.6 dBm and \(-\)1 dBm, respectively. For a larger V\({}_{\rm DD}\) of 1 V, a better IIP3 of 1 dBm is achieved (not shown here). Table 1 is a summary of the 28 GHz down-conversion mixer and recently reported state-of-the-art mm-wave CMOS down-conversion mixers [1; 2; 3; 4; 5; 6; 7]. As can be seen, the mixer in this work is designed and implemented via a relatively cost-effective 90 nm CMOS process and achieves better overall performance than the mixer implemented with the costlier 40 nm CMOS technology in [6]. If a more advanced CMOS process is used for the mixer in this work, the overall performance can be further enhanced. This means that the proposed down-conversion mixer architecture has high potential for mm-wave communication systems. Overall, compared with that in [1; 2; 3; 4; 5; 6; 7], our mixer occupies a medium chip area, requires a medium LO\({}_{\rm in}\), consumes low power, and achieves prominent CG, f3 dB, NF, LO-RF isolation, and IIP, and one of the best FOM\({}_{\rm 1}\)s and FOM\({}_{\rm 2}\)s. The remarkable results indicate that the proposed down-conversion mixer architecture is suitable for 28 GHz 5G NR and even a higher frequency system. Figure 9: Measured and simulated (**a**) CG and NF versus RF frequency, and (**b**) CG and NF versus IF frequency characteristics of the mixer. Finally, it would be informative to provide readers with a futuristic vision about what the future holds for us as we move forward [16; 17; 18; 19]. Considering the saturation of the state-of-the-art microelectronic technologies in providing a faster operation speed, nowadays, hybrid optoelectronic platforms are considered a new solution to expand the operation bandwidth, while we can still enjoy the CMOS technology for implementing such hybrid systems.