Study of variability performance of CMOS active inductors

The development of CMOS technology has led to the integration of communication circuits on a single chip. Inductors constitute an essential part of a RF front ends. Employment of spiral inductors has put several limitations on such RF circuits. Spiral inductors are fixed, bulky, cover large area and can’t be scaled with the process technologies. Also, due to the resistive losses and substrate losses, the quality factor is limited. An alternate way to emulate inductor behavior is using active inductors. Active inductors are area-efficient, support tunable inductance, quality factor, self-resonant frequency and can be scaled with process technologies. However, the active inductors are too sensitive to process, supply voltage and temperature variations. In this paper, four active inductor architectures i.e. basic, resistive feedback, Weng-Kuo and regulated cascode active inductor are designed. The quality factor performance of the four active inductor circuits is evaluated. Further, to demonstrate the performance of active inductors, bandpass filter configurations are implemented. The impact of process, voltage and temperature variations on the quality factor of active inductors and resonant frequency of bandpass filters is studied. Simulations are carried out at 180-nm technology node.