부산대학교 도서관

Feedback control for self-triggering frequency modulation is proposed for an integrated buck-boost DC-DC converter in an AMOLED display. The goal is to reduce the ripple noise and transient time during the switching process. The converter uses two control modes: switching frequency modulation (SFM) mode for light load current and pulse width modulation (PWM) mode for heavy load current, which result in high power efficiency over a wide range of load current. The mode is automatically changed according to the load current and triggering pulse. A ring-type voltage controlled oscillator (VCO) is applied to obtain a proper operating frequency in the feedback control circuit by the load-dependent current source. The set and reset pulses are used to limit the switching-on time in the sensing signals with less transient time. The converter was fabricated with 0.35-µm BCD (BIPOLAR-CMOS-DMOS) process technology. An experiment shows that the maximum power efficiency is 90 percent over a wide current range of 10-150 mA. Compared to a conventional converter, the proposed converter shows significantly less ripple noise and transient time.