High-resolution wide-band LC-VCO for reliable operation in phase-locked loops

This paper presents a novel sizing scheme to implement the array of switches in the capacitor bank of LC-VCOs for oscillation frequency coarse control. The proposed scheme allows increasing the number of elements in the capacitor bank beyond the values typically achieved by binary scaling, endowing the resulting LC-VCO with a wider tuning range and high frequency resolution, which is beneficial for the implementation of reliable phase-locked loops. Two different gigahertz LC-VCOs have been designed to validate the proposed scheme. The prototypes, fabricated in a cost-effective 0.18 μm CMOS process, cover a 700 MHz frequency range from 1.35 GHz to 2.05 GHz and from 2.05 GHz to 2.75 GHz, respectively, with a phase noise figure of−122 dBc/Hz and −119.5 dBc/Hz at 1 MHz from the mid-range carriers, and a power consumption of 18 mW. These figures result in a respective FOMT of −186.4 dBc/Hz and −183.8 dBc/Hz. The performance of the fabricated LC-VCOs is achieved in each case with a dense coarse tuning range of 128 levels, which allows, respectively, a fine tuning gain smaller than 40 MHz V−1.