Balanced-to-Doherty Mode-Reconfigurable Power Amplifier With High Efficiency and Linearity Against Load Mismatch

Abstract

A balanced-to-Doherty (B2D) mode-reconfigurable power amplifier (PA) is presented in this article, which is endowed with a unique capability of maintaining high linearity and high efficiency against load mismatch. The Doherty operation of this PA is based on a new Doherty PA (DPA) architecture configured from an ideal balanced amplifier, named quasi-balanced DPA (QB-DPA). This article, for the first time, analytically proves that the QB-DPA is functionally equivalent to a standard DPA. Most importantly, this new discovery enables PA reconfiguration between the Doherty and balanced modes. With the tunability implemented using a silicon-on-insulator (SOI)-based single-poledouble-throw (SPDT) switch, a reconfigurable B2D PA prototype using GaN technology is demonstrated at 3.5 GHz, exhibiting the state-of-the-art linear DPA performance in the nominal 50-Ω load condition. Specifically, the Doherty mode achieves a continuous-wave measurement efficiency of 70% and 54.5% at the maximum output power of 41.9 dBm and 6-dB power backoff, respectively. In the modulated long-term evolution (LTE) evaluation, the DPA exhibits -37-dB adjacent channel power leakage (ACPR) and 2.36% error vector magnitude (EVM) at the maximum rated power of 34.5 dBm while achieving a 42.4% efficiency. It is experimentally demonstrated that the Doherty (QB-DPA) mode is well resistant to load mismatch with high efficiency across a majority portion of the 2:1 voltage standing wave ratio (VSWR) circle, while the combination of Doherty and balanced modes can ensure a constantly linear performance of the B2D PA (e.g., 2.2%-5% of EVM) under the entire mismatch condition.