A lumped‐element balun design with multi‐interference suppression for push–pull power amplifier

Abstract

SummaryIn this article, a lumped‐element balun with multi‐interference suppression is implemented and presented. Originated from the conventional lattice LC balun, the balun combining two Π‐networks is expended to four new topologies. By constructing frequency traps and out‐of‐phase combining pathways, the new topologies can realize two‐ or three‐interference suppression while maintaining well‐matched input/output impedances. The concept is studied theoretically in both even and odd mode circuits, and analytical design equations are also derived. Based on the design theory, four interference suppression balun topologies are proposed for push–pull power amplifiers. To verify the design concept, two of the four topologies working at 1 GHz are prototyped and measured. The measured results agree well with the analysis and simulation results. The two baluns both achieve good performance with low insertion loss better than −3.9 dB, low return loss less than −13.6 dB, good interference suppression more than 24.7 dB, and small phase unbalance less than 0.8°. Furthermore, the proposed balun is used in a gallium nitride push–pull power amplifier to validate the 2nd and 3rd harmonic suppression. The amplifier works at 1 GHz with a typical gain of 16.7 dB. At least −45 dBc interference suppression, 52.6% power‐added efficiency, and 34.6 dBm P1dB output power are obtained.