K-band low phase noise Class-C VCOs using DGS inductor in CMOS technology

This work presents two new structures of inductor to improve the performance of K-band class-C voltage controlled oscillators (VCOs) in 0.18-mu m CMOS technology. Conventional inductor provided by the foundry suffers from a poor-quality (Q-) factor large area and low self-resonance frequency. These problems are solved by introducing defected ground structure using the lower layers. The first DGS inductor is a meander-line finger capacitor under C-shape inductor while the second inductor is three loops with finger DGS. The fabricated inductor has wideband characteristics, and additionally, the Q-factor is increased almost by 84% compared to a single loop inductor without DGS. The measured differential inductance and quality factor of the proposed inductor are 180 pH and 30 at K-band. The proposed inductors are used to design a high-performance class-C VCO at K-band. Furthermore, class-C biasing decreases the current drawn from 2.9 mA to 0.8 mA, so the figure of merit (FoM) is improved by 4 dB compared to conventional VCO. The NMOS class-C VCO achieves a frequency tuning range (FTR) from 25 GHz to 26 GHz and has a FoM of -198dBc/Hz whereas the second class-C VCO has a frequency range from 18.9 GHz to 19.8 GHz and phase noise at 1 MHz offset changes from-111.3 to -114.2dBc/ Hz.

Automated summary

This work presents two new structures of inductor to improve the performance of K-band class-C VCOs. By introducing defected ground structure, the problems of poor-quality factor and low self-resonance frequency of conventional inductors are solved. The proposed inductors have wideband characteristics and increased Q-factor, allowing for the design of high-performance VCOs.