Vdc Vcas Vdc Driving Stage Doherty Stage Vcas M5 Vsense M1 R1 M2 R2 Vggc M6 ABN Vs1 Vctrl1 Carrier Vggc Vcas Vs2 Vcas RFin Vctrl2 M8 M3 M4 PP M7 Vctrl2 Load Vdc Peaking Vdc Vctrl1 Figure 15. Circuit diagram of 60 GHz CMOS Doherty [55]. at the PA output was used to combine the power from two identical unit PAs that used the proposed Doherty technique. Two transformer-based E-band Doherty PAs were designed and measured. The first implementation achieved 16.2 dBm output power with a P1dB of 15.2 dBm when using a 0.9-V supply. The second implementation demonstrated 21 dBm output power with a PAE of 13.6% with a 1.5-V supply. The PAE at 6-dB back-off remained high at 7%. In [57], a 45 GHz active phase-shift Doherty PA was proposed and implemented in 45-nm SOI CMOS. The quarter wave-length transmission line at the input of the auxiliary amplifier was replaced by an amplifier. This increased the gain and PAE by more than 1 dB and 5%, while at the same time reducing the die area to 0.45 mm2. At 6-dB back-off power, the PAE was 21%. In [58], a generalized network synthesis approach was proposed that allowed simultaneous frequency and back-off reconfigurability at mm-waves. The PA architecture maintained high-efficiency with spectrally efficient codes proposed across a wide frequency range. The method was based on the synthesis of a multi-port combiner network that exploited the interaction of mm-wave PAs switched symmetrically to synthesize the optimal impedances across the 2-D space of reconfiguration: frequency and back-off. As a proof of concept, a Doherty FOURTH QUARTER 2020 Carrier Amplifier (Class-AB) M/2 Cout Lp /2 Input Peaking Amplifier (Class-C) M/2 Cout RL Cout Lp /2 Figure 16. Schematic of transformer-based Doherty PA [56]. PA was presented using 0.13 μm SiGe BiCMOS process. It operated across the 30-55 GHz frequency band with a peak Psat of 23.7 dBm at 40 GHz, output collector efficiency of 34.5% and 22% at saturation and 6-dB back off point, respectively. It maintained a collector efficiency > 16% at 6-dB back off across the whole frequency range. In [59], the 28-/37-/39-GHz linear Doherty PA used silicon for broadband fifth generation applications was presented. A new transformer based on-chip power combiner IEEE CIRCUITS AND SYSTEMS MAGAZINE 59