Analysis and Implementation of High-Q CT Inductor for Compact and Wide- Tuning Range Ku-Band VCO

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. For the proposed CT inductor, despite its size is miniaturized by 51%, the Q -factor is increased by 41% in the frequency range of 5-30 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. The proposed CT inductor is used to design a compact and wide-tuning-range VCO at Ku-band in 0.18- \mu \text{m} complementary metal-oxide-semiconductor (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 \mu \text{m}\,\,\times400\,\,\mu \text{m} only. The VCO chip oscillates from 11.7 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 the dc power consumption of the VCO core is 4 mW which results in a figure of merit (FoM) normalized to the die area (FoM _{\mathrm {A}} ) to be -197 dBc/Hz.