A 0.5-V 560-kHz 18.8-fJ/Cycle On-Chip Oscillator With 96.1-ppm/°C Steady-State Stability Using a Duty-Cycled Digital Frequency-Locked Loop

On-chip oscillators are popular clocking solutions for a wide range of circuits and systems due to their ease of integration and low form factor, but their energy efficiency is typically limited to the pJ/cycle range by a number of contributors, such as active biasing currents, frequency dividers, and comparators. This work presents an on-chip oscillator for energy-efficient Internet-of-Things (IoT) applications based on a duty-cycled digital frequency-locked loop (DFLL) that reduces energy by disabling energy-hungry components and only periodically reactivating them to keep the output frequency stabilized during temperature drifts. A test chip is implemented in 65-nm CMOS and achieves 18.8 fJ/cycle (10.5 nW at 560 kHz) while maintaining an average steady-state temperature stability of 96.1 ppm/°C from 0 °C to 100 °C.