A 2.5-to-3.3GHz CMOS Class-D VCO

Abstract

Power consumption in LC oscillators for wireless communications is a popular research topic, where the Class-C oscillator has been proposed to improve the efficiency of the standard Class-B oscillator (most often referred to as cross-coupled differential-pair LC-tank oscillator). In this work, we introduce the Class-D oscillator to further reduce power consumption for a desired phase noise level. Class-D oscillators have been known since 1959, but their use in GHz applications had to wait for nm CMOS processes offering excellent switches with manageable parasitic capacitances. The VCO has been designed in a standard 65nm CMOS process without any thick metal layer. The LC tank, employing a single-turn four-finger 0.59nH inductor, has a Q of 10-11 at 3GHz, estimated from post-layout simulations (including PCB) fitting the measured power consumption.