A Novel Variable Inductor Using a Bridge Circuit and Its Application to a 5–20 GHz Tunable LC-VCO

A novel variable inductor using a bridge circuit is proposed. Because of a bypass switch MOSFET placed at a balance point, the effect of the switch resistance which is a penalty of the variable inductance is suppressed and degradation of the Q factor is mitigated. A 10-20 GHz tunable LC-VCO core using this inductor was also fabricated. Because of the multi-stage variable inductor, 20 GHz operation having over 10 GHz continuous tuning range with phase noise of -103 to -84 dBc/Hz is achieved with only 5.2 to 7.1 mW power consumption. By using a 1/2 divider, a 5-20 GHz continuous tuning range is also obtained. The chip area is 1/10 smaller than that of conventional wide range LC-VCOs because of the miniature 3-D structure variable inductor. This variable inductor and the wide range LC-VCO are suit able for the clock generation of high-speed communication systems, multi-core processors, as well as low-power, low-cost wireless transceivers.