Design of DC-DC Converters for Smart Mobile Applications

Abstract

In today’s consumer market, battery-operated mobile electronic devices such as smartphones, tablet PCs, and other devices are in great demand. Modern smart mobile devices perform complex function and require more compact physical size. Therefore, the design consideration for dc-dc converters with fast-transient response is needed to provide good dynamic performance for mobile processors. In addition, in order to reduce the size and weight of mobile devices, miniaturization of power modules is essential. Therefore, this dissertation is focused on design techniques to resolve these requirements. To provide fast-load transient response, the current-mode DC-DC converter is presented. The current-sensing circuit, which is the key building block of the current-mode DC-DC converter, is proposed in the dissertation. A lossless current sensing technique to measure the inductor current by measuring current through the power transistor is proposed. The inaccuracy caused by voltage and temperature variations is compensated by using a self-trimming technique. By adding a proposed circuit that reduces the error caused by temperature and input voltage variations, we were able to achieve a sensing accuracy of over 93%, a 13% improvement over a conventional circuit. This dissertation also presents an area-efficient fully-integrated DC-DC buck converter, which is able to provide significant cost reduction. Packaging inductors and on-chip capacitors are used to elimination of bulky and expensive off-chip LC components. The packaging inductors include parasitic inductances of the bonding wires and lead frames in the package. They have significantly better Q factors than the best on-chip inductors implemented on silicon. Finally, a multiple-output switched-capacitor (SC) DC-DC converter, which is able to significantly reduce PCB area, is presented. In general, multiple SC converters, which have the large number of passive elements and large active area, are required to control individual brightness of red-green-blue (RGB) LEDs. The proposed multiple-output converter can reduce the number of passive components and active area by using only one flying capacitor and sharing internal circuits. The converter has three outputs for individual brightness control of red-green-blue (RGB) LEDs, and each output directly regulates the current, due to the V-I characteristics of LEDs, which are sensitive to PVT (process, voltage, temperature) variations. All of these converters presented in this dissertation are fabricated using standard CMOS processes. The validations of proposed converters are verified through HSPICE simulation and measurement results of the fabricated chips.