Input Harmonic Controlled Broadband Continuous Class-F Power Amplifiers for Sub-6 GHz 5G Applications
A comprehensive analysis is presented for investigating the effects of input nonlinearity on performance and broadband design of continuous mode class-F power amplifiers (PAs). New time-domain waveforms are derived considering input and output harmonic terminations for continuous mode class-F operation. The derived design equations show that the typical fundamental load design space of a continuous class-F PA must be re-engineered in presence of second harmonic input nonlinearity to a new design space in order to achieve optimum class-F PA performance versus varying second harmonic load impedance. For the practical validation, the impacts of input nonlinearity on the performance of continuous-mode class-F PAs are first confirmed with pulsed vector load pull (VLP) measurements on a low power GaN 2 mm device.
Second, a broadband high power GaN 24 mm part is designed following the proposed theory with in-package input second harmonic terminations targeting 1.75-2.3 GHz frequency band for sub-6 GHz 5G high-power applications. Efficiency higher than 65% with peak power more than 53.2 dBm was maintained over the target frequency band, with excellent flatness. Third, a Doherty PA is implemented based on the designed GaN 24 mm part to evaluate the broadband performance with modulated stimuli. Using a multi-carrier signal having an instantaneous bandwidth of 395 MHz, the average drain efficiency of the Doherty PA at 8 dB output back-off is higher than 44% and the linearized adjacent channel power ratio (ACPR) is better than -52 dBc.
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