Performance characteristics of an ultra-low power VCO

A CMOS voltage controlled oscillator (VCO) with ultra-low power capabilities is described. A discussion of the VCO´s performance characteristics and modeling in terms of simple physics-based expressions is presented. The oscillators have been designed in a commercial 0.18 μm CMOS technology and the transistors in the VCOs operate from weak to strong inversion modes at supply voltages from 80 mV to 1.8 V. A new and important feature of this VCO is the use of the substrate voltage as an additional control for the frequency tunability. The detailed experimental results and comparison to calculations are presented and discussed.