I/Q-Sharing Switched-Capacitor Power Amplifier with Baseband Harmonic-Rejection and Wilkinson Combiner

Abstract

The CMOS switched-capacitor power amplifier (SCPA) proposed in 2011 [1]-[2] achieved much higher system efficiency than conventional transmitter architectures. In this paper, SCPA linearity is also analyzed and improved with new techniques. Specifically, a baseband harmonic-rejection (BBHR) technique is used to minimize the counter third-order intermodulation products (C-IM3). Also, using a Wilkinson combiner, the cross-coupling between two sub-SCPAs is isolated to enable a linear harmonic-rejection summation. With the proposed topology, the linearity is improved significantly compared to a conventional I/Q-sharing SCPA. More specifically, the C-IM3 is reduced by ~25 dB with a single-tone input and by ~22 dB with modulated signal.