Design of a Digitally Controlled Tunable Matching Network Based on GaN FETs

Abstract

Radio frequency (RF) power amplifiers are integral to many academic, medical, and industrial applications. In many of these applications, dynamic impedance matching is a critical requirement. While conventional tunable matching networks (TMNs) with motor-controlled variable inductors/capacitors provide excellent matching range, their response times are inadequate for applications with rapid load changes. This paper presents a design of digitally controlled TMNs suitable for quick impedance matching at high frequencies (10s of MHz) and high power levels (100s of Watts). Our proposed matching system employs a secondary high-speed TMN based on wide bandgap GaN field effect transistors configured as digitally controlled variable capacitors in a double Pi network. The prototype system, tested at 13.56 MHz and 500 W, achieves impedance matching for loads with reflection coefficients up to 0.5 at any angle with less than 1% reflected power. Unlike techniques requiring device switching at RF frequency, our approach offers a simpler implementation while maintaining high power handling capability.