A 30-GHz Switched-Capacitor Power Amplifier for 5G SoCs

Switched-capacitor power amplifier has gained popularity within the radio frequency integrated circuit community, since it is CMOS compatible offering high integration density and good performance particularly in terms of linearity. In this paper we present a study on the use of switched-capacitor power amplifier at millimeter-wave frequency range. We identify the major design challenges in this paper, and demonstrate the feasibility of switched-capacitor power amplifier with a 30-GHz design case. Our analysis describes the effects of power amplifier device parasitics and their contribution to dynamic power consumption, revealing that these are a major factor in degradation of switched capacitor power amplifier efficiency at millimeter waves. Two circuits, one for 3 GHz and the other for 30 GHz, were designed and simulated with 28-nm bulk CMOS technology. At 3 GHz, the designed switched capacitor power amplifier structure with 6-bit resolution features maximum output power of 19.4 dBm and efficiency of 59% whereas the output power of 18.6 dBm with 21% efficiency is achieved at 30 GHz. The switched-capacitor power amplifier preserves its good linearity at higher frequencies as well, and our design demonstrates an adjacent channel leackage ratio of -34.4 dB at 30 GHz for a 100-MHz OFDM-modulated signal.