Abstract: A method to calibrate I/O cell current has been described. The method includes setting a global control value provided to the I/O cells. Then, for each I/O cell, the method includes comparing the logic voltage at the output pad of the I/O cell with a reference voltage, and sinking more current at the output pad by enabling additional driver bits associated with the I/O cell if the logic voltage is higher than the reference voltage, or sinking less current at the output pad by disabling additional driver bits associated with the I/O cell if the logic voltage is lower than the reference voltage.

Abstract: A local driver circuit to drive a logic voltage at an output pad includes an adder having K bits to add a K-bit control value to a local value, the adder producing a K-bit calibrated value. The circuit further includes K field-effect transistors (FETs), the drain of each FET being coupled to the output pad, and logic circuitry to perform a logical-AND function between a data input and the K-bit calibrated value. The logic circuitry providing a K-bit output with each of the K output bits being coupled to the gate of a corresponding one of the FETs. A comparator produces a correction value from a comparison of the logic voltage at the output pad and a reference voltage. A control unit sets a least significant bit (LSB) portion of the local value responsive to the correction value so as to make the logic voltage at the output pad in the reference voltage substantially equal.