Dispersion and Stability Properties of Microwave Tunable Negative Inductance in CMOS Technology

This paper reports on the analysis of a tunable negative inductor based on a Negative Impedance Inverter (NII) loaded with positive capacitance. The analysis is based on one-pole model of the amplifiers used in the negative impedance inverter. As such, the model introduces the dispersion of the generated negative input inductance and the parasitic input conductance. In addition, the developed model is loaded with an external RL network that mimics a common practical scenario, and a stability analysis is performed. In the last step, a tunable negative inductor was designed in 40-nm CMOS technology to verify the previous analysis. The designed circuit produces a nearly dispersionless inductance of -350 pH to - 85 pH up to 10 GHz with Q > 10 octave bandwidth. The proposed implementation is well suited for MMIC technology as it avoids the use of on-chip inductors unlike designs based on negative impedance converters.