Impedance calibration circuit, memory controller including the impedance calibration circuit and memory system including the memory controller

An operating method of an impedance calibration circuit, comprising:

• electrically connecting the impedance calibration circuit to an external resistor via a first pad by activating an impedance adjustment enable signal;
• performing a first impedance calibration operation to generate a first impedance calibration code set for adjusting a resistance value of a first terminating resistor to a first target value, with reference to a resistance value of the external resistor;
• and
• while performing the first impedance calibration operation, performing a second impedance calibration operation to generate a second impedance calibration code set for adjusting a resistance value of a second terminating resistor to a second target value, different from the first target value, using at least a part of the first impedance calibration code set.

A memory controller, comprising:

• a first impedance calibration part directly connectable to an external resistor via a first pad and configured to generate a first impedance calibration code set for adjusting an resistance value of a first terminating resistor to a first target value, with reference to a resistance value of the external resistor;
• a second impedance calibration part configured to generate a second impedance calibration code set for adjusting an resistance value of a second terminating resistor to a second target value different from the first target value, with reference to a reference resistance unit, a resistance value of which is set to a second resistance value according to at least a part of the first impedance calibration code set received from the first impedance calibration part;
• a transceiver connected to a second pad and configured to receive the first impedance calibration code set from the first impedance calibration part;
• and
• a receiver connected to a third pad and configured to receive the second impedance calibration code set from the second impedance calibration part,
• wherein the second pad has a different structure from the third pad.