A Transformer-Based Dual-Coupled Triple-Mode CMOS LC-VCO

This paper introduces a transformer-based, dual-coupled, triple-mode voltage-controlled oscillator (VCO) using a transformer-based fourth-order tank with tunable transconductance feedback between the primary and secondary coils. The tank impedance can be reshaped by the transconductors through the tuning of their biasing currents. By controlling the bias currents, the VCO has three different operational modes, capable of generating a single frequency in either the 3- or 5-GHz band as well as two frequencies in the 3- and 5-GHz bands simultaneously. The measured phase noise at 1-MHz offset frequency is -109.5 and -118.8 dBc/Hz when the oscillator oscillates at a single frequency of 5.24 or 3.22 GHz, respectively. The phase noise is -104.3 and -112.6 dBc/Hz, respectively, when the oscillator oscillates at 5.34 and 3.03 GHz simultaneously. The triple-mode VCO was fabricated in a 0.13- μm CMOS process, occupies a core area of 0.16 mm ², and dissipates 5.6 mW from a 1.2-V supply.