A 5-GHz CMOS LC Quadrature VCO With Dynamic Current-Clipping Coupling to Improve Phase Noise and Phase Accuracy

This paper presents a quadrature voltage-controlled oscillator (QVCO) employing a proposed dynamic current-clipping coupling technique to provide around 90 degrees phase shift in the coupling paths. The phase shift given by the coupling network not only improves the phase noise, but also desensitizes the phase error to component mismatches in the QVCO. The coupling network furthermore reduces the noise injected into the LC tank at the most vulnerable time (zero crossing points). The proposed current-clipping coupling allows the use of a strong coupling ratio to minimize the quadrature phase sensitivity to mismatches without degrading the phase noise performance. The proposed QVCO is implemented in a 130-nm CMOS technology. The measured phase noise is - 121 dBc/Hz at 1-MHz offset from a 5-GHz carrier. The QVCO consumes 4.2 mW from a 1-V power supply, resulting in an outstanding figure of merit of 189 dBc/Hz.