The invention relates to a source driver and a composite level shifter. The source driver comprises a data buffer circuit, a plurality of level shifters and a plurality of driving circuits. The data buffer circuit receives and registers a plurality of pixel data during a driving period. The level shifters convert the voltage levels of the pixel data registered in the data buffer circuit during the driving period. The driving circuits generate a plurality of source signals according to the converted pixel data during driving period. The data buffer circuit may comprise a plurality of composite level shifters for converting the voltage levels of the pixel data, and latching the converted pixel data.