Stacked-ring oscillator with reduced phase noise

We designed an inverter-based ring oscillator with reduced phase noise for low-power wireless sensor networks. The proposed structure is based on two stacked oscillating rings reusing the same current, and improves the phase noise performance without increasing total power dissipation. Theoretical analysis shows that a maximum phase noise reduction of 50% can be achieved. Simulations based on a 0.18 -mum CMOS technology confirm our analysis.