A source driver for display devices includes line pair driving blocks. Each of the line pair driving blocks includes a de-multiplexing portion for de-multiplexing first and second digital data to generate first and second de-multiplexing data, a decoding portion for decoding the first and second de-multiplexing data to generate first and second analog data, and a multiplexing portion for multiplexing the first and second analog data to generate first and second gradation voltages. In the source driver, the de-multiplexing portion is controlled by signals having information of loading timing for the digital data and information of polarity for the gradation voltages.