Combined Pulse-frequency Modulation and Multiphase Interleaving Techniques for Ultra-low Ripple in Dual-output Switched Capacitor Buck Converter in Wearable Systems
摘要
This paper presents an ultra-low ripple and high-efficiency dual-output switched capacitor (SC) converter intended for wearable biomedical applications. Pulse-frequency modulation (PFM) and a multiphase interleaving technique are integrated with reduce output ripple and enhance efficiency, in comparison with individual methods. Real-time PFM adjustments of switching frequency in response to load variation actively compensate the coarse ripples, while interleaving minimizes fine ripples. Four sub-SCs are paralleled to design the main SC converter for multiphase interleaving, and the switching bit control provides two distinct output voltage levels. The SC converter, operating as a step-down, functions with two conversion ratios, 2/3 and 1/4, within an input voltage range of 1.1–1.5 V. The output voltages of the converter are 800 mV and 200 mV, and the output current ranges are 500 nA–320 µA and 5 nA–4 µA, respectively. The proposed SC is simulated in TSMC 65 nm CMOS technology, and occupies an area of 1.31 mm2. The simulated results show a maximum power efficiency of 96.97% and an output power of 256.6 µW from 1.2 V input voltage.