An 82.3- to 87.4-GHz modified differential Colpitts VCO in 0.18-µm CMOS

Abstract

A millimeter-wave 0.18-µm CMOS VCO with measured oscillation frequency from 82.25 to 87.43 GHz is presented in this paper. In this work, three varactor rows are utilized to improve the VCO tuning range. The first varactor row is deposited at bottom of the cross-coupled pair for alleviating the loading effect on the VCO core. Moreover, the other two varator rows are connected between the drain and source terminations of the cross-coupled pair for enhancing the tuning range. Compared to conventional differential Colpitts VCO, the loading effects on VCO core can be effectively alleviated. In addition, due to the second-harmonic superposition technique, the signal strength of the output signal (2f_o) can be enhanced. The enhanced 2f_o output signal is extracted from the middle of the varactors, resulting in an elimination of the required λ/4 micropstrip or coplanar waveguide (CPW) line for a RF choke. This leads to a minimized chip size of 0.549 mm². Based on the proposed VCO architecture, the fabricated 0.18-µm CMOS VCO core consumes 5.8-mW low dc power at 1.0-V supply voltage. At this bias condition, the measured phase noise is −77.92 dBc/Hz at 1-MHz offset from an 84.02-GHz carrier, and the tuning range is 6.11%. Notably, this modified differential Colpitts VCO demonstrates the highest operation frequencies (82.25 GHz to 87.43 GHz) among previously published 0.18-µm CMOS VCOs.