This work presents a new structure of center tap (CT) inductor to improve the performance of Ku-band Voltage-Controlled Oscillators (VCOs). Conventional CT 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 a coupling structure. In the proposed CT inductor, in spite of its size is miniaturized by 51 %, the Q-factor is soared by 41 % in the frequency range of 5 GHz to 30 GHz compared to a conventional CT inductor. The measured differential inductance and quality factor of the proposed inductor are 385 pH and 22 at 12 GHz. Later, the proposed CT inductor is employed to design a compact and wide tuning-range voltage-controlled oscillator (VCO) at Ku-band in 0.18 µm CMOS technology, and this leads to 5.8 dB phase noise improvement compared to the use of a conventional CT inductor. The fabricated VCO has a compact core size of 140 µm × 400 µm only. The VCO chip oscillates from 11.7 GHz to 13.7 GHz. The measured phase noise is -107.7 dBc/Hz at 1 MHz offset frequency at a carrier frequency of 13.7 GHz, and dc power consumption of the VCO core is 4 mW which results in a figure of merit (FoM) normalized to the die area (FoMA) to be -197 dBc/Hz. |
