A 4.12 GHz, 3.3 mW VCO with 87.9% tuning range using a transformer-based variable inductance

Abstract

A wide-band LC-tank CMOS voltage controlled oscillator (VCO) employing a transformer-based variable inductance structure is presented. The variable inductance is obtained through a switching scheme that controls the current path in a transformer and allows four different inductances to be delivered by the structure. Additionally, an electric model of the transformer obtained through the simulated data and equations based on its physical properties is proposed. The inductance and quality factor from the variable structure were extracted from the transformer’s electromagnetic simulations and model’s scattering parameters. The model showed and error lower than 4% in all modes of operation inside of the desired range (from 1 to 6 GHz). The proposed VCO is simulated and shows a percentual tuning range of 87.9% around a central frequency of 4.12 GHz, while consuming less than 3.3 mW of power and exhibiting a maximum phase noise of -108 dBc/GHz occupying an area of 0.45 mm2.