Minimum Energy Tracking Loop With Embedded DC–DC Converter Enabling Ultra-Low-V oltage Operation Down to 250 mV in 65 nm CMOS

Abstract

Minimizing the energy consumption of battery-pow- ered systems is a key focus in integrated circuit design. This paper presents an energy minimization loop, with on-chip energy sensor circuitry, that can dynamically track the minimum energy oper- ating voltage of arbitrary digital circuits with changing workload and operating conditions. An embedded DC–DC converter which enables this minimum energy operation is designed to deliver load voltages between 0.25 V to 0.7 V. The minimum energy tracking loop along with the DC–DC converter and test circuitry were fabri- cated in a 65 nm CMOS process. The area overhead of the control loop is only 0.05 mm /50. Measured energy savings of the order of 50%–100% are obtained on tracking the minimum energy point (MEP) as it varies with workload and temperature. The DC–DC converter delivers load voltages as low as 250 mV and achieved an efficiency 80% while delivering load powers of the order of 1 W and higher from a 1.2 V supply.