A Study of 24 GHz 3D-Striped Inductor VCO with Gradually Changed Metal Width of Inductor

The phase noise characteristics of the 24-GHz 3D-striped inductor VCO with gradually changed metal width of inductor has been investigated. In the high frequency region such as beyond 20-GHz, the striped inductor VCO ensure to obtain lower phase noise compare than normal inductor VCO, and the optimum metal fixed width is existing. In this work, we focused on the striped inductor which metal width changed gradually from inner to outer to consider current crowding effect. In concretely, one is the inner metal finger is the widest and the outer metal finger is the narrowest, and the other is vice versa, the inner metal finger is the narrowest and the outer metal width is the widest. The measurement results of VCOs with the constant fixed finger width inductor, the outer-widest width, and the inner-widest width all exhibit approximately -103 dBc/Hz minimum phase noise at 1-MHz offset from 24 GHz oscillation frequency, but the current consumption at achieving the lowest phase noise are 10.9 mA, 11.6 mA, 9.2 mA, respectively. This result shows that the VCO which adopted the striped inductor with metal width change gradually from inner-wide to outer-narrow shows the lowest current consumption. The process technology in this work is TSMC-180 nm CMOS.