A novel CMOS active inductor with high quality factor, high linearity and mutually independent tuning of inductance and quality factor

A novel CMOS active inductor (CAI) circuit topology is proposed. It consists of two identical gyrators, a voltage-controlled negative resistance cell (VCNRC) and a voltage-controlled current source (VCCS). And each gyrator is composed of a feedforward transistor, a feedback transistor, a cascaded transistor, a common-source (CS) transistor, and a feedback resistor. Moreover, these two gyrators are symmetric and form a differential structure. By above building blocks configuration and cooperation, the CAI can achieve following different performances. First, high quality factor (Q) can be achieved by a combination of the VCNRC, the cascaded transistors and the feedback resistors due to the decrease in the equivalent resistance losses; Secondly, high linearity can be realized by the additional CS transistors due to the compensation for the nonlinear drain current of the feedback transistors. Thirdly, mutually independent tuning of inductance (LCAI) and Q can be achieved by tuning three external bias voltage terminals respectively configured in the cascaded transistors, the VCNRC and the VCCS. The verification results show that at the frequency of 2.0 GHz, the peak Q can be tuned from 555 to 2780 with a large tuning range of 400.9 %, while the LCAI can be maintained within a small variation of only 0.9 %; on the other hand, LCAI at 2.0 GHz can also be tuned from 158 nH to 212 nH while the Q value has a variation of only 4.2 %; moreover, the CAI also is demonstrated to have inductance linearity as high as +0.17 dBm, and occupies a compact effective area of 43 μm × 52 μm. In addition, the output noise voltage at 2 GHz is 3.1 nV/√Hz, and both LCAI and Q values also exhibit good robustness against process corner and temperature variations. These comprehensive results highlight the CAI excellent performances in terms of size, Q value, linearity, mutually tunability of LCAI and Q, noise performance as well as the robustness against process and temperature variations.