An 11/19-GHz VCO using switchable transformer in 0.18-µm CMOS

This paper presents a novel switchable transformer to enhance the quality factors, to reduce the chip area, and to increase the inductance tuning range. The proposed switchable transformer is applied to an LC-tank of a VCO which is designed with two wide oscillating frequency bands. By controlling the switches of the transformer, the dual-band VCO verified in a 0.18-μm CMOS can operate at two wide bands. The post-simulation phase noises are -101 dBc/Hz and -90 dBc/Hz at 1 MHz offset at 11 GHz and 19 GHz, respectively. Moreover, the tuning range is 13% at 11 GHz and 6% at 19GHz. The chip area is merely 0.3mm².