Self-start-up fully integrated DC-DC step-up converter using body biasing technique for energy harvesting applications

An ultra-low power, self-start-up switched-capacitor Two Branch Charge Pump (TBCP) circuit for low power, low voltage, and battery-less implantable applications is proposed. In order to make feasible the low voltage operation, the proposed charge pump along with Non-Overlapped Clock generator (NOC) are designed working in sub-threshold region by using body biasing technique. A four-stage TBCP circuit is implemented with both NMOS and PMOS transistors to provide a direct load flow. This leads to a significant drop in reverse charge sharing and switching loss and accordingly improves pumping efficiency. A post-layout simulation of designed four-stage TBCP has been performed by using an auxiliary body biasing technique. Consequently, a low start-up voltage of 300 mV with a pumping efficiency of 95% for 1 pF load capacitance is achieved. The output voltage can rise up-to 1.88 V within 40 ps with 0.2% output voltage ripple in case of using 400 mV power supply. The designed circuit is implemented by 180-nm standard CMOS technology with an effective chip area of 130.5 pm x 141.8 mu m while the whole circuit consumes just 3.2 mu W.