E- and D-Band Common-Base Power Amplifiers in SiGe-BiCMOS with Performance Enhanced by Current Clamping and Device Stacking

With 5G established and 6G research ongoing, rising capacity drives the exploration of higher frequency bands. Power amplifiers (PA) drain most of a transceiver’s power. Still, maintaining efficiency at higher frequencies is challenging, with much of the power dissipated as heat. While common-emitter (CE) output stages are typical at lower frequencies, common-base (CB) stages offer superior gain, linearity, and thermal stability. Additionally, it is shown that the base-emitter junction can be naturally exploited to implement current-clamping, such that DC current tracks the peak signal current, allowing PAs to have the superior Class B efficiency profile in back-off while maintaining the higher gain and linearity of Class-A —a critical feature for systems employing modulation schemes with high Peak-to- Average Power Ratios (PAPR). To further boost output power, transistor stacking has been explored, with emphasis on optimizing the number of stackable stages and employing techniques to preserve voltage swing despite losses. Experimental results are presented for several PAs and a power mixer, designed in SiGe BiCMOS processes, operating in the E- and D-bands. The PAs achieve output power levels approaching 20 dBm, with double-digit peak PAE and demonstrating a 2 to 3 times back-off PAE improvement over silicon PAs operating in comparable frequency ranges.