A 3 GHz CMOS quadrature oscillator using active superharmonic coupling

A 3 GHz quadrature oscillator has been designed, fabricated, and measured using CMOS 0.18 mum technology. The oscillator uses an active superharmonic coupling technique to generate the quadrature signals. By using two identical LC differential oscillators with a 180deg relationship enforced between the second-order harmonics that are present at the common- mode nodes, quadrature outputs are obtained at the fundamental frequency. Quadrature oscillations were achieved at 3.0 GHz with a measured output power of -6 dBm. The phase error in the fundamental quadrature outputs is less than 6deg and the power consumption for the core of the oscillator is 7.5 mW. The phase noise performance is -116 dBc/Hz at a 1 MHz offset and the figure of merit is -177 dBc/Hz. The layout for this circuit is very compact at 650 mum times 500 mum.