Integrated Switched-Capacitor Voltage Regulator
Project
Integrated Switched-Capacitor Voltage Regulator
Principal Investigator
Oracle Principal Investigator
Hesam Fathi Moghadam, Research Director
Summary
Efficient, stable, and fast power delivery against fluctuating workloads have become a critical concern for applications from battery-powered devices to high-performance servers. With high density on-chip or package-integrated capacitors, integrated switched-capacitor (SC) voltage converters provide high efficiency down-conversion from a battery or off-chip voltage regulation modules. A number of SC voltage converters and regulators have been proposed recently that show higher efficiency at increasingly wider range of output voltages [1-9]. At each output voltage point, however, the load current could still fluctuate causing large voltage droops, and the conversion efficiency could degrade at different load currents with sub-optimal converter designs.
Literature on the voltage regulation of switched-capacitor converters has primarily focused on output voltage comparison against reference voltage [1-9]. To provide optimal voltage converter performance and efficiency across the two dimensions of voltage and current, we postulate that current sensing along with voltage comparison would be a necessity. On-chip current sensing has been employed in a number of previous buck converter designs for the purpose of current-mode feedback control [10-11]. However, load current sensing has not been largely adopted for SC converters, since they are mainly based on voltage-mode charge and discharge operations.
This project aims to expand on the initial works done by Arizona State University on current-sensing-based workload optimization techniques as well as understand the tradeoffs between using on-chip capacitors and package-integrated capacitors to implement the SC voltage converters.
References
[1] H.-P. Le, et al., “Design techniques for fully integrated switched-capacitor DC-DC converters,” IEEE Journal of Solid-State Circuits (JSSC), vol. 46, no. 9, 2011.
[2] Y. Ramadass, et al., “A fully-integrated switched-capacitor step-down DC-DC converter with digital capacitance modulation in 45 nm CMOS,” IEEE Journal of Solid-State Circuits (JSSC), vol. 45, no. 12, pp. 2557-2565, 2012.
[3] G. Patounakis, et al., “A fully integrated on-chip DC–DC conversion and power management system,” IEEE Journal of Solid-State Circuits (JSSC), vol. 39, no. 3, 2004.
[4] T. Anderson, et al., “A sub-ns response on-chip switched-capacitor DC-DC voltage regulator delivering 3.7W/mm2 at 90% efficiency using deep-trench capacitors in 32nm SOI CMOS,” Int. Solid-State Circuits Conf. (ISSCC), 2014.
[5] L. Chang, et al., “A fully-integrated switched-capacitor 2:1 voltage converter with regulation capability and 90% efficiency at 2.3A/mm2,” Symposium on VLSI Circuits, 2010.
[6] J. Seo, et al., “Deep trench capacitors for switched-capacitor voltage converters,” Int. Workshop on Power Supply on Chip, 2012.
[7] R. Jain, et al., “A 0.45-1V fully integrated reconfigurable switched capacitor step-down DC-DC converter with high density MIM capacitor in 22nm tri-gate CMOS,” Symposium on VLSI Circuits, 2013.
[8] S. Bang, et al., “A fully integrated successive-approximation switched-capacitor DC-DC converter with 31mV output voltage resolution,” Int. Solid-State Circuits Conf. (ISSCC), 2013.
[9] L. G. Salem and P. P. Mercier. “An 85%-efficiency fully integrated 15-ratio recursive switched-capacitor DC-DC converter with 0.1-to-2.2V output voltage range,” Int. Solid-State Circuits Conf. (ISSCC), 2014.
[10] C.-F. Lee and P.-K.-T. Mok, “A monolithic current-mode CMOS DC-DC converter with on-chip current-sensing technique,” IEEE Journal of Solid-State Circuits (JSSC), vol. 39, no.1, pp. 3-14, Jan. 2004.
[11] C.-Y. Leung, et al., “A 1.2V buck converter with a novel on-chip low-voltage current-sensing scheme,” Int. Symposium on Circuits and Systems (ISCAS), 2004.