Differential VCO design with a wide frequency tuning range

New differential stacked spiral inductors were employed in our design of VCOs fabricated using the CMOS 0.18 μm technology in this paper. The frequency tuning range of these VCOs were extended significantly, and the measured oscillation frequencies cover from 1.69 to 2.1375GHz, with 23.3% tuning range and phase noise about −118.41 dBc/Hz at 1MHz theoretically. The core current of these VCOs is about 25mA at 1.8V supply voltage. What is more, the VCO designed only occupies on-chip area of 365 × 504μm
²
, which is much smaller than that of other VCOs reported in the literature recently.