Patent ID: 7348945

Claim:
A digital-to-analog converter (DAC), used in an electro-luminescent (EL) display panel, the EL display panel comprising a substrate and at least one pixel, the substrate having a first area and a second area, the at least one pixel comprising a first thin film transistor (TFT) and an EL device, the first TFT being disposed in the second area for driving the EL device according to a pixel current, the DAC comprising: a plurality of switch circuits disposed in the second area, each having at least one second TFT, each switch circuit being selectively turned on according to the corresponding grey level; and a plurality of current sources disposed in the first area, each having at least one third TFT, each current source being electrically connected to the corresponding switch circuit and selectively supplying current to generate the pixel current according to conducting states of the corresponding switch circuit, wherein the TFT formed in the first area has a first channel doping concentration; the TFT formed in the second area has a second channel doping concentration; and in a low-temperature polysilicon manufacturing process, a first threshold voltage variation of the TFT formed in the first area is less than a second threshold voltage variation of the TFT formed in the second area.