A digital-to-analog (D/A) converter comprises a decoder apparatus and an operational amplifier. The decoder apparatus comprises first and second decoder unit. The first decoder unit selects a voltage of first voltage set as first and second voltage in response to a value of first gray level set. The second decoder unit selects first border voltage of second voltage set as the first and the second voltages and second border voltage of that as the first and the second voltages in response to the maximum and the minimum value of second gray level set respectively. The second decoder unit further selects the first and the second boarder voltage as the first and the second voltage respectively in response to an intermediate value of the second gray level set. The operational amplifier generates a pixel voltage having level between the first and the second voltage accordingly.