An IO driver for an integrated circuit and a method for calibrating such an IO driver are provided. The IO driver comprises a plurality of IO driver cells, a plurality of IO partial driver cells and an external resistor. The IO driver cells control IO operations for a corresponding plurality of data channels of the integrated circuit. The IO partial driver cells are coupled to respective cells of the plurality of IO driver cells. The external resistor provides a reference impedance. The reference partial driver cell is coupled to the external resistor and is arranged to determine the reference impedance and to provide information depending on the reference impedance to the IO partial driver cells. The IO partial driver cells are arranged to calibrate the respective IO driver cells based on the provided information.