An impedance adjustment circuit for controlling an impedance of a variable impedance circuit includes 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. The calibration circuit may be configured to generate the reference current based on a reference resistor coupled thereto. In particular, the calibration circuit may be configured to match a current in the replica of the variable impedance circuit and a current in the reference resistor to generate the voltage at the replica of the variable impedance circuit.