A 0.4 V CMOS Current-Controlled Tunable Ring Oscillator for Low-Power IoT and Biomedical Applications

This work presents a current-controlled CMOS ring oscillator (CCRO) optimized for ultra-low-voltage applications in next-generation energy-constrained systems. Leveraging bulk voltage tuning in 22 nm FDSOI differential inverter stages, the topology enables frequency adjustment while operating MOSFETs in the subthreshold region—critical for minimizing power in sub-1 V environments. Simulations at 0.4 V supply demonstrate robust performance: a three-stage oscillator achieves a 537–800 MHz tuning range with bias current (IBIAS) modulation from 30–130 nA, while a four-stage configuration spans 388–587 MHz. At 70 nA IBIAS, the three-stage design delivers a nominal frequency of 666.8 MHz with just 10.23 µW power dissipation, underscoring its suitability for ultra-low-power IoT and biomedical applications. The oscillator’s linear frequency sensitivity (2.63 MHz/nA) allows precise, dynamic control over performance–power tradeoffs. To address diverse application needs, the design integrates three tunability mechanisms: programmable capacitor arrays for coarse frequency adjustments, configurable stage counts (three- or four-stage topologies), and supply voltage scaling. This multi-modal approach extends the operational range to 1 MHz–1 GHz, ensuring compatibility with low-speed sensor interfaces and high-speed edge-computing tasks. The CCRO’s subthreshold operation at 0.4 V—coupled with nanoampere-level current consumption—makes it uniquely suited for battery-less systems, wearable health monitors, and implantable medical devices where energy efficiency and adaptive clocking are paramount. By eliminating traditional voltage-controlled oscillators’ complexity, this topology offers a compact, scalable solution for emerging ultra-low-power technologies.