24 GHz Low-Phase-Noise VCO Using 3D-Striped Inductor Utilized Thin-Metal Layers

The utilization of thin-metal inductor in a 24-GHz low-phase-noise voltage-controlled oscillator (VCO) is demonstrated. The low-phase-noise LC-VCO can be realized by using a thick-metal inductor since the phase noise of the VCO strongly depends on the Q-factor of the inductor. However, the advantage of the Q-factor of the thick-metal inductor no longer exists in the high-frequency region above 20 GHz since the parasitic resistance increases due to skin and proximity effect. Thin-metal inductor can be utilized in a high-frequency inductor with some technique. In this study, a 3D-22 striped inductor that consists of 22 fingers by using two thin-metal layers, and a 3D-44 striped inductor that consists of 44 fingers by using four thin-metal layers are used as inductors of VCOs. The measurement results of the minimum phase noise of VCOs that adopted the 3D-22 striped inductor, the 3D-44 striped inductor, and the conventional thick metal inductor all exhibit -101 dBc/Hz at 1-MHz offset from 24 GHz oscillation frequency, and the current consumptions are 12 mA, 9 mA, and 7.5 mA, respectively under 1.8 V supply voltage. This result shows that the phase noise of the 3D striped inductor VCO matches that of the conventional inductor VCO with only 20% higher current consumption. The process technology in this work is TSMC-180 nm CMOS.