A low power tunable inductor based on active capacitor with negative resistance

A method to provide a low power tunable inductor is presented in which the inductance and its equivalent series resistance can be independently tuned. This equivalent series resistance can be also set to negative or zero value that is corresponding to inductor with ideal quality factor. In this method, a varactor is placed in parallel with a passive inductor and then, an active capacitor is placed in series with them. To this end, a low power Tunable Active Capacitor (TAC) is proposed which is capable of generating tunable capacitor and large negative resistance to compensate the loss of tunable inductor circuit. Also, the power consumption is low because of using a diode-connected transistor. A prototype of the proposed circuit is designed and simulated at 4 GHz. The electromagnetic simulation results show the inductance tuning range of 0.48-2.3nH with zero or even negative equivalent series resistance is obtained while the power dissipation is less than 3 mW. Moreover, noise analysis shows that higher inductance translates to lower noise while there is a weak correlation between noise and quality factor of the obtained inductances.