A Programmable Impedance Tuner with a High Resolution Using a 0.18-um CMOS SOI Process for Improved Linearity

In this paper, a novel coupler/reflection-type programmable electronic impedance tuner combined with switches that were fabricated by a 0.18-um complementary metal–oxide–semiconductor (CMOS) silicon-on-insulator (SOI) process is proposed for replacement of the conventional mechanical tuner in power amplifier (PA) load-pull test. By employing the multi-stacked field-effect transistors (FETs) as a single-branch switch, the proposed tuner has the advantage of precise impedance variation with systematic and magnitude and phase adjustment. Additionally, it led to high standing wave ratio (SWR) coverage and a good impedance resolution with a high power handling capability. Furthermore, the double-branch based on multi-stacked FET was applied to switches for additional enhancement of the intermodulation distortion (IMD) performance through the mitigated drain-source voltage of the single-FET. Drawing upon the measurement results, we demonstrated that SWR changed from 2 to 6 sequentially with a 12–15° phase angle step over a mid/high-band range of a 1.5–2.1 GHz band for 3G/4G handset application. In addition, the PA load-pull measurement results obtained using the proposed tuners verified their practicality and competitive performance with mechanical tuners. Finally, the measured linearity using the double-branch switch demonstrated the good IMD3 performance of −78 dBc, and this result is noteworthy when compared with conventional electronic impedance tuners.