DC-DC converter with auto-switching between PWM and PFM and OLED display using the same

摘要

A DC-DC converter with auto-switching between pulse width modulation (PWM) and pulse frequency modulation (PFM) is used in an organic light emitting diode (OLED) display and judges power consumption of an OLED array of the display according to display data of the display and thus determines a switching time between PWM and PFM. The converter comprises a content statistic unit, an auto-switching control unit, a PWM controller, a PFM controller and a power generator. The content statistic unit receives and accumulates the display data of the OLED display and then outputs a statistic value. The auto-switching control unit outputs a control signal according to the statistic value to control the PWM controller and the PFM controller and to switch to a PWM mode or a PFM mode.

主权项

1. A DC-DC converter with auto-switching between pulse width modulation (PWM) and pulse frequency modulation (PFM), for providing a power voltage to an organic light emitting diode (OLED) display, the DC-DC converter comprising:
a content statistic unit, for accumulating display data from the OLED display and then outputting a statistic value, wherein the display data represent a luminance of each pixel, and the statistic value represents an average power consumption of a display period; an auto-switching control unit, for generating a switch control signal according to the statistic value, wherein the switch control signal has a first state and a second state; a PWM controller, for generating a PWM power when the switch control signal is in the first state, wherein the PWM power is adapted for driving a heavy load; a PFM controller, for generating a PFM power when the switch control signal is in the second state, wherein the PFM power is adapted for driving a light load; and a power generator, coupled to the PWM controller and the PFM controller, for outputting the PWM power or the PFM power as the power voltage, wherein the PWM power is outputted when the statistic value is higher than a preset value, which represents the OLED display will operate in the heavy load, and the PFM power is outputted when the statistic value is lower than the preset value, which represents the OLED display will operate in the light load, wherein the content statistic unit comprises: a look-up-table, for recording a weighting corresponding to power consumption of each pixel value, and thus outputting a corresponding weighting according to the display data; a multiplier, for receiving the display data and the weighting and thus outputting weighting data; a register; and an adder, for receiving the weighting data, adding the weighting data to a stored value of the register to generate an added value, and storing the added value back to the register; and wherein the content statistic unit further receives a vertical sync signal, outputs the stored value of the register as the statistic value when the vertical sync signal is enabled, and then clears the stored value of the register.