A gate-modulated CMOS LC quadrature VCO

A quadrature voltage-controlled oscillator (QVCO) based on the time-varying gate-modulated coupling of two LC tank VCOs is introduced. Using a standard 0.18 mum CMOS process, the new topology is compared to the conventional series QVCO in terms of start-up loop gain, quadrature phase accuracy, phase noise, tuning range, and voltage headroom characteristics. In addition to comparable phase noise performance, the gate-modulated QVCO (GM-QVCO) also exhibits superior quadrature phase accuracy, and suitability for low power supply voltage designs that use cascode current sources and active loads. It draws 2.4 mA from a 1.8 V power supply, displays a phase noise of -122 dBc/Hz @ 1 MHz offset, and has a quadrature phase error of 0.4deg.