SYNCHRONOUS DC-DC BUCK CONVERTER FOR REDUCING ELECTROMAGNETIC INTERFERENCE USING DIGITAL DELAY LOCKED LOOP AND METHOD FOR CONTROLLING SHAPING OF SWITCHING SIGNALS

A synchronous DC-DC buck converter according to the embodiments of the present invention generates a dropped output voltage by using a first switch which applies an input voltage to an inductor for the duty period of a first switching signal and a second switch which is switched with a second switching signal which is complementary to the first switching signal. The synchronous DC-DC buck converter includes a sawtooth wave generating unit which generates a sawtooth wave with a frequency according to a frequency set signal, a driving oscillation signal generating unit which generates an error voltage of a reference voltage and the output voltage and generates a driving oscillation signal with a duty ratio corresponding to the amplitude of the error voltage by comparing the sawtooth wave with the error voltage, a switching signal generating unit which generates the first and second switching signals to have a waveform applying a dead time in the duty period of the driving oscillation signal, and a phase tracking unit which generates the frequency set signal based on an adding signal to add a frequency variation signal according to a diffusion spectrum clock set voltage to an activation period length signal of a pulse corresponding to a phase difference of a reference clock signal and the driving oscillation signal.