26.5 A Watt-Level Quadrature Switched/Floated-Capacitor Power Amplifier with Back-Off Efficiency Enhancement in Complex Domain Using Reconfigurable Self-Coupling Canceling Transformer

Modern wireless communication systems in portable devices require transmitters (TXs) with watt-level output power (Pout), high data-rate, and high efficiency, especially at power back-off (PBO) for enhanced average efficiency. CMOS digital TXs demonstrate high integration and high efficiency at low cost, which are attractive attributes in practical applications. Compared to polar TXs, quadrature TXs [1-6] show the advantages of a simpler architecture (without CORDIC and phase modulator) and higher data-rates. IQ cell sharing is used to increase the peak efficiency of quadrature TXs [2]. Besides, to achieve enhanced efficiency at PBO, various techniques are developed for digital TXs and digital power amplifiers (DPAs), such as Class-G Doherty [4], load modulation [5], hybrid Doherty with impedance boosting [6], 8 way-combined switched-capacitor power amplifier (SCPA) with a switched transformer [7], and time-interleaving Class-G Doherty [8], etc. In this work, a watt-level switched/floated-capacitor power amplifier (SFCPA) using reconfigurable self-coupling canceling transformer and IQ cell sharing is proposed, which achieves efficiency enhancement at 3/6/9/12/15dB PBOs in the complex domain without any supply switching.