Ultra-low power VCOs - performance characteristics and modeling (invited)

The paper describes CMOS voltage controlled oscillators (VCOs) with ultra-low power capabilities. It presents a discussion of their performance characteristics and modeling using simple physics-based expressions. 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. They have been tested and found functional with supply voltages from 80 mV up to 1.8 V. Experimental results show that the VCO´s power consumption is mainly dynamic for the whole range of supply voltages used and powers down to the nW regime has been achieved. A new and important feature of this VCO is the use of the substrate voltage as an additional control for the frequency tunability. In this way, a new VCO with two voltage controls for its operating frequency has been realized. The detailed experimental results and comparison to calculations are presented and discussed.