A second-harmonic LC-quadrature voltage controlled oscillator with direct connection of MOSFETs’ substrate

Abstract

This work introduces a new low noise second-harmonic quadrature voltage controlled oscillator (QVCO) made by coupling two identical cross-connected LC voltage controlled oscillators. In each of the core oscillators the substrate nodes of the MOS varactors, and also the substrate nodes of the cross-connected MOSFETs are configured in such a way that they act as common mode nodes. Then the core oscillators are coupled together via direct connection of the substrates of the MOS varactors in one of the core oscillators to the substrates of the cross-connected MOSFETs in the other core oscillator, and vice versa. No extra elements are used for coupling of the two core oscillators and therefore no extra noise sources are imposed on the circuit. Operation of the proposed QVCO was investigated with simulation using a commercial 0.18 μm RF CMOS technology: it shows a power dissipation of 9.7 mW from a 1.8 V supply voltage and a simulated phase noise of ?125.5 dBc/Hz at 1 MHz offset from center oscillation frequency of 5 GHz. Since the tail transistor can be eliminated, the proposed QVCO can operate with supply voltages as low as 0.5 V, as confirmed with simulation.