Biography
Enrollment Date: 2002
Graduation Date：2005
Degree：M.S.
Defense Date：2005.06.14
Advisors：Zhiliang Chen Chen Jia
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：A Buck DC-DC Converter with Digital PID Compensation
Abstract:
The short of the energy and the worse case of the air pollution is one of the most serious problem of the world, and the main lose of energy is from the voltage converter. So the voltage converter circuits are playing a important role of the market. Cellular phone, MP3, MP4, Li-ion battery charge circuits and some other portable devices have been developed, and the power management market is booming these years. The accuracy and ripple of output voltage and the conversion efficiency will influence the stability and the battery life of these systems. Now digital controlled DC-DC converters are becoming more and more popular, which have improved the stability of supply voltage, temperature and process corner. Then the switching frequency, stability and the ripple of the output voltage will be greatly improved. The market analysis shows that digital controlled DC-DC converters is one of the most popular fields and the good products for IC market. This thesis shows the principle and arithmetic of the PID controller. And also designs the ADC, digital control law, Bandgap and DPWM circuit. Layout of this design has been tape out at HJTC 0.18um CMOS process. The active chip area is 0.16mm2 Through the test result of the chip, when the input voltage is 3V, output voltage is 1.25V, the switching frequency is 1MHz, load current is at the typical value 200mA, and the output voltage ripple is less than 10mV. And when the load current is 500mA, reach the maximal efficiency 88%. With the analysis of test result, some improvements of this circuit are proposed. First, dither pattern controller is used to increase the equivalent resolution of DPWM output. Second, variable delay cell is proposed to improve the response on supply voltage. And finally, use Sigma-Delta modulator to increase the resolution of the DPWM and decrease low frequency ripple of the output. Some of this circuits and layouts are all finished and will tape out at HJTC.