Tunable inductance using transmission lines

This paper presents a concept of a tunable inductance using coupled transmission lines. The proposed method suggests applying signal at one line of a shorted coupled transmission line and injecting current at the other line of the coupled pair. This way the inductance value can vary proportionally with the ratio of the currents in the coupled lines. A detailed analytical discussion is presented. A circuit level implementation of this concept is also presented. In order to confirm this effect in measurement, we have realized a test circuit in 28 nm CMOS technology. Measurements show that equivalent inductance seen at the input of the transmission lines can be controlled by input voltage. Equivalent inductance can be tuned continuously and an inductance tuning factor higher than 10 is achieved.