1-D Reconfigurable Pseudo-Doherty Load Modulated Balanced Amplifier With Intrinsic VSWR Resilience Across Wide Bandwidth

Abstract

This article presents the first-ever wideband pseudo-Doherty load-modulated balanced amplifier (PD-LMBA) with load-mismatch tolerance through 1-D reconfiguration. It is theoretically unveiled that when the control amplifier (CA, as a carrier) in PD-LMBA is driven to its saturation, it is endowed with a duality between the current source (CS) and voltage source (VS), which makes the BA (as peaking) have complementary load-modulation trajectories for the two sub-amplifiers (BA1 and BA2) under load mismatch. As a result, the BA in PD-LMBA inherits the intrinsic load insensitivity from the generic quadrature-balanced amplifier. Meanwhile, the saturation power of CA can be maintained by only reconfiguring the dc bias voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DD,CA}}$ </tex-math></inline-formula> ) that solely depends on the real part of load impedance, real <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm (Z_{\mathrm {L}})$ </tex-math></inline-formula> . As such, the degree of freedom for PA reconfiguration and load sensing (ideally) is minimized to 1-D, and the entire PD-LMBA can maintain a nearly constant efficiency profile against arbitrary load mismatch. The theoretical analysis is well verified using emulated circuit model, and it is further experimentally validated by a prototype designed with GaN transistors and wideband quadrature hybrids. As a proof of concept, the fabricated PD-LMBA circuit achieves state-of-the-art performance in measurement at matched load with 1.7–2.9 GHz of bandwidth, 65%–77% of drain efficiency at peak power of 39–43 dBm, and 55%–71% of efficiency at 10-dB output back-off (OBO). More importantly, the prototype also experimentally exhibits excellent mismatch resilience through 1-D reconfiguration, which is demonstrated at three representative in-band frequencies of 1.7, 2.1 and 2.5 GHz at 2:1 VSWR. Specifically, a maximum drain efficiency from 51.9% to 72.8% at peak power is achieved over the entire 2:1 VSWR circle, and an efficiency up to 65.4% is measured at 10-dB back-off. Modulated evaluation using an LTE signal is also performed, in which the 1-D reconfigurable PD-LMBA exhibits an excellent average efficiency at load mismatch that aggressively outperforms the state-of-the-art.

Topics & Concepts