DESIGN OF TRANSFORMER BASED LOAD COMBINER FOR FULLY INTEGRATED POWER AMPLIFIER AT MM-WAVE FREQUENCIES

Abstract

The Doherty Power Amplifier (DPA) is gaining favour in base-station and broadcast applications, rapidly replacing standard Class B amplifiers due to its simplicity and efficiency. Despite their success, real DPA implementations have had restricted RF bandwidth, especially at higher power levels. This limitation is due to the common operating classes used for active devices, as well as the bandwidth constraints associated with standard impedance inversion approaches. In this work, we will talk about advances in microwave engineering and RF circuits, with a focus on the creation of a 47 GHz transformer-based power combiner for a single-chip wireless transceiver. A comparison to contemporary Doherty power amplifier designs is offered, with a focus on a unique symmetrical series combining transformer designed to improve back-off efficiency while maintaining linearity. In addition, an uneven Doherty combiner designed for 47 GHz in 130nm SiGe BiCmos technology is presented and optimised for WLAN applications. A novel design strategy for a Doherty power amplifier without a lumped π-network is given, allowing active load modulation inside a compact structure, resulting in greater linearity and efficiency during back-off. The transformer-based power combiner achieved up to 72% power-added efficiency (PAE) at 6 dB back-off and 78% PAE at saturation, while the center-tapped transformer achieved up to 72.7% PAE at 6 dB back-off and 77.6% PAE at saturation. Furthermore, a center-tapped transformer balun developed for 47 GHz in 130nm SiGe BiCmos technology achieves low magnitude and phase imbalances over a broad bandwidth. Optimising coil width and offset is critical for establishing balance and minimising insertion loss. Experiments reveal a 0.189 dB imbalance and less than 1º phase deviation over the frequency range of 43 to 53 GHz.