1. An organic light emitting diode driver comprising: a converting unit having predetermined gray scale ranges and converting input data into compensation data set as a representative value of a gray scale range, to which a gray scale level of the input data belongs, in order to selectively compensate for pixel deterioration depending on whether the input data has been calibrated or not; a driving unit driving pixels of a pixel unit based on the compensation data from the converting unit; and a compensating unit providing the converting unit with a deterioration compensation signal based on a difference between at least two level signals, each containing the representative value from the converting unit and deterioration information obtained from a pixel driven by the driving unit.