Design of power-efficient adiabatic charging circuit in 0.18μm CMOS technology

In energy supply applications for low-power sensors, there are cases where energy should be transmitted from a low-power battery to an output stage load capacitor. This paper presents an adiabatic charging circuit with a parallel switches approach that connects to a low-power battery and charges the load capacitor using a buck converter which operates in continuous conduction mode (CCM). A gate controller of parallel switches (GCPS) is used to increase the duty-cycle of the input signal of buck converter switches, which controls the inductor current and charges the load capacitor in 256 steps. The proposed parallel switches approach is used to improve the energy efficiency under different powers transmission and comprises a current sensor, comparator, R-S latch, parallel pMOS switches, and parallel nMOS switches. For high powers transfer, the large switches are paralleled with small switches and result in conduction losses reduction. Also, for low powers transfer, the total switching losses are significantly reduced by turning off the large PMOS/NMOS switches during the charging operation. The proposed circuit was designed and simulated in a 0.18μm CMOS technology. The efficiency of the proposed circuit during the capacitor charge-up cycle is more than 80% for average input powers between 0.5mW to 30mW.