Efficiency enhancement of a tunable RF power amplifier by second harmonic manipulation using thin-film BST varactor

This paper presents an idea of efficiency enhancement of a tunable class-AB radio frequency power amplifier (RF PA) utilizing a tunable resonant circuit along with tunable matching at the output using barium-strontium-titanate (BST) varactors. It is demonstrated that application of appropriate bias voltages across tunable output 2^nd harmonic termination as well as matching network, comprising of BST varactors, results in continuously tunable performance of RF PA. Power added efficiency (PAE) along with other performance parameters such as gain and output power, are shown to be adapted as the RF PA is tuned for multiband operation from 1.8 to 2.0 GHz. For class-AB operation, an improvement of up to 8% in PAE and up to 0.5 dBm in output power were observed in saturated output power range provided the output harmonics are properly terminated.