Design and implementation of a compact CMOS DC-to-DC converter

Abstract

DC-DC Converter has been popular nowadays due its use in fast emerging market of portable devices and it is used primarily to step down or step up the input voltage to a constant output voltage. In current technology, most of portables devices are getting smaller and the manufacturer pack many utilities inside them. Hence, a compact DC-DC Converter will be attractive in the sense that it achieves high performance while still addressing the low cost design issues. Faster response of the DC-DC Converter is also needed to protect the supplied circuit. Previously for current-mode DC-DC converter, an error amplifier and voltage comparator are mandatory blocks and the designers’ choice. This project offers an alternative by using a current comparator to compare the feedback signals. Furthermore, the design of the current sensing block is simplified. Full transistor design of current-mode DC-DC using voltage comparator and current comparator are done in this project. A fair comparison between these two topologies is done in 0.18μm CMOS process. The operating frequency is 1 MHz and the supply voltage is 2.8-3.6V. The new topology has around 40% improvement in transient response and 36% improvement in output voltage change compare to the current topology. Improved load and line regulation are also observed in the simulation. The output ripple voltage is about 6-8 mV with 8μH inductor and 8μF capacitor. The power efficiency is over 80% for load current 100 to 400mA.