Based On Sigma-delta Modulation, Low Noise And High Efficiency Buck Dc-dc Converter Realization

The architecture innovation and performance promotion of electrical system cannot do without the support of high-performance power supply. While designing SMPS (switching-mode power supply), efficiency and noise performance are always the greatest consideration, especially in the application of portable electronic products and wireless communication system.Some research effort on improving efficiency and noise performance of SMPS is explored in this thesis. As to improving efficiency, high-efficient power MOSFET driving technology and circuit implementation are presented. The proposed MOSFET driver includes dead time controller, DCM controller and gate width controller. These controllers can improve efficiency from different aspects. In dead time controller, a novel auto-adaptive circuit based on charge-pump is proposed. In width controller, current-sensing circuit is improved. Traditional current-sensing circuit samples the peak current of power MOSFET, it requires the switching signal of power MOSFET has fixed duty cycle. Because of the different modulation method, the duty cycle varies. It make impossible to sampling peak current. A novel current-sensing method, sampling averaging current, is proposed to resolve this problem. As to reducing noise, a current popular technology, sigma-delta modulation, is introduced into the design of SMPS. First, the noise characteristic of PWM modulation and sigma-delta modulation are compared. And some theoretical problems are analyzed when applying sigma-delta modulation. In the circuit implementation, a second-order, continuous time modulator is designed, and the current feedback method is improved. The improvement reduces the power consumption of OTA and improves the performance of modulator. In addition, a low noise, high efficiency synchronous buck converter with a fully integrated second order single-bit continuous time sigma delta modulator based controller is designed and fabricated on a 0.35um CMOS process. Measurement results conform to the theoretical analysis and circuit simulation results.