Study of SOI CMOS tunable capacitor architectures and application to antenna aperture tuning

In this paper, a small-signal analysis of two SOI CMOS digitally tunable capacitor architectures intended for RF antenna tuning is provided. A mathematical model is derived and used to compare both architectures in terms of quality factor (Q-factor). The architecture with better Q-factor has been selected for implementation in a 130 nm SOI CMOS technology. To evaluate its potential for antenna aperture tuning applications, the fabricated tunable capacitor chip has been used as a tuning device into a printed notch antenna. Measurement results show that the designed tunable capacitor allows the resonance frequency of the tunable multiband antenna to be tuned from 520 MHz to 920 MHz (55 % tuning range) with a radiation efficiency in the range of 18 % to 54 %.