A Dual-Output Switched Capacitor DC-DC Buck Converter Using Adaptive Time Multiplexing Technique in 65-nm CMOS

This paper presents an area- and power-efficient dual-output switched capacitor (DOSC) dc-dc buck converter for wearable biomedical devices. The DOSC converter has an input voltage range between 1.05 and 1.4 V and generates two simultaneous regulated output voltages of 1 and 0.55 V. The DOSC consists of two main blocks: a switched capacitor regulator and an adaptive time multiplexing (ATM) controller. The switched capacitor regulator generates a single regulated voltage using pulse frequency modulation based on a predetermined reference voltage. In addition, the ATM controller generates two simultaneous output voltages and eliminates the reverse current using pulse width modulation during the switching between the output voltages. Addressing the reverse current problem is important to reduce the output voltage droop and improve the performance. The proposed converter supports load currents of 10- 350~\mu \text{A} and 1- 10~\mu \text{A} at load voltages of 1 and 0.55 V, respectively. The DOSC circuit is fabricated in 65-nm CMOS, and it occupies an active area of 0.27 mm 2 . Measured results show that a peak efficiency of 78% is achieved at a load power of 300~\mu \text{W} .