Patent ID: 7295033

Claim:
An impedance adjustment circuit for controlling an impedance of a variable impedance circuit that comprises a pull-down circuit and a pull-up circuit connected to a signal node configured to be connected to an external source and/or load, the impedance adjustment circuit comprising: a calibration circuit including a replica of the variable impedance circuit and configured to generate an impedance control signal for the variable impedance circuit based on a voltage generated at the replica of the variable impedance circuit in response to a reference current; wherein the calibration circuit is configured to generate the reference current based on a reference resistor coupled thereto; wherein the replica of the variable impedance circuit comprises a replica of the pull-down circuit and a replica of the pull-up circuit; wherein the calibration circuit is configured to generate a current in the replica of the pull-down circuit and to apply a first impedance control signal to the pull-down circuit and to the replica of the pull-down circuit based on a voltage generated at the replica of the pull-down circuit in response to the current in the replica of the pull-down circuit; and wherein the calibration circuit is further configured to generate a current in the replica of the pull-up circuit and to apply a second impedance control signal to the pull-up circuit and to the replica of the pull-up circuit based on a voltage generated at the replica of the pull-up circuit in response to the current in the replica of the pull-up circuit.