A DAC includes a gamma voltage generator for generating a plurality of gamma voltages, and a decoder for receiving an M-bit digital value for selecting one of the gamma voltages, wherein the decoder comprises a first thermometer encoder, a first selector and a second selector. The first thermometer encoder is utilized to receive N bits of the digital value to generate a first thermometer code with 2N bits, wherein N is smaller than M, and M and N are positive integers. The first selector has a plurality of selecting groups, each selecting group having 2N switches controlled by the first thermometer code to output one gamma voltage, where the second selector receives the gamma voltages outputted by the selecting groups of the first selector and outputs one gamma voltage selected from the received gamma voltages based on the (M−N) bit of the digital value.