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A 1.8V 2.5-to-5.2 GHz dual-input two-stage CMOS voltage-controlled ring oscillator (VCO) is presented. A novel delay cell used for the two-stage ring VCO is proposed to achieve low power dissipation and better phase noise performance. The delay cell adopts both inductive-peaking and shunt-shunt feedback circuit techniques to obtain high gain and wide. Implemented in a 0.18 μm CMOS technology using 1.8V supply voltage, the VCO has a wide operating frequency range from 2.5GHz to 5.2GHz with coarse-tune VCO gain of 4.75GHz/V and fine-tune VCO gain of 80MHz/V. At 3.6GHz, the phase noise of the VCO is -90.1dBc/Hz at 1MHz frequency offset with low power consumption of 17mW. Because of the two-stage ring topology, the VCO can provide quadrature outputs. The total chip area is 0.4mm × 0.6mm.