A Fully Differential CMOS Active Inductor with High Quality Factor and High Tunability

In this paper, a CMOS active inductor for wideband application is proposed. Active inductors have some advantages such as high quality factor, small size, and high tuneability. The proposed circuit is realized by exploiting the intrinsic capacitance of the transistor and uses a cross-coupled pair of transistors providing negative feedback for enhanced quality factor. The circuit is biased with a controllable current source varying the feedback and tuning the inductor. The proposed active inductor is designed by TSMC RF-CMOS 0.18 μm technology and simulated using Advanced Design System (ADS). Simulation results show a wide inductive bandwidth (up to 9.5 GHz), a very high resonance frequency over 5 GHz, and independent tuning of the inductance (0.4-18.73 nH) and the quality factor (up to 2850) values. Its power consumption is about 1.26 mW with power supply of 1.8 V. In addition, the proposed active inductor exhibits a very low level of noise (less than 4.6 √nV/Hz) over the bandwidth of 1-9.6 GHz), enabling its application to the implementation of high-quality factor low-noise LC tank in high-frequency building blocks of RF front-end.