High-Efficiency Power Amplifier Using an Active Second-Harmonic Injection Technique Under Optimized Third-Harmonic Termination. - Seo, Mincheol; Lee, Hwiseob; Gu, Jehyeon; Kim, Hyungchul; Ham, Junghyun; Choi, Wooyeol; Yun, Yanghun; O, Kenneth K.; Yang, Youngoo (IEEE Trans. Circuits Syst. II Express Briefs, 2014)