Abstract: The present invention is related to a unit gain buffer of the driver circuit to drive the data line in the filed of LCD data driver, further to be preferably applied to the new TFT-LCD processing of low temperature poly-silicon. This invention is using the plurality of PMOS transistor connection to result in the almost same value between the Vout and Vin. There is no using of the feedback connection in this invention, so the using of the compensation capacitor can be avoided, furthermore the data driver layout area of the LCD driver can be reduced. This invention can improve the defect of the larger layout area result from the prior art.