A source driver having a structure of adjusting voltage with speed is suitable for use in a panel displaying apparatus for driving a display array unit. The structure of adjusting voltage with speed has a logic speed monitoring unit, an internal logic voltage generator, a substrate voltage generator, a substrate leakage-current monitoring unit, and a power management control unit. In this manner, by monitoring the logic operation speed of an internal logic circuit in the source driver, in accordance with the change of the operation frequency, the power is dynamically adjusted, so as to optimize a condition between the power consumption and the operation speed. And, in the standby mode, the power consumption is further reduced by adjusting the substrate voltage. Also and, according to the substrate leakage current of the source driver, the substrate voltage can also be adjusted.