Circuit and method for calibrating resistors for active termination resistance, and memory chip having the circuit

A method of calibrating an active termination resistor, the method comprising:

• comparing voltage at a pad, to which an external resistor is connected, with a reference voltage, and outputting a first comparison signal corresponding to the comparison result;
• calibrating a first variable resistor to have the same resistance as that of the external resistor in response to the first comparison signal until voltage at the pad is identical with the reference voltage;
• comparing voltage at the pad and voltage at a second variable resistor, and outputting a second comparison signal corresponding to a comparison result;
• calibrating the second variable resistor to have the same resistance as that of the external resistor in response to the second comparison signal;
• and
• calibrating the active termination resistor to have the same resistance as that of the first variable resistor and/or the second variable resistor.

A circuit for calibrating an active termination resistor to have the same resistance as that of an external resistor, the circuit comprising:

• a first control circuit for comparing voltage at a first node, to which the external resistor is connected, with a reference voltage, and for outputting a first control code controlling a first variable resistor that supplies electric current to the first node;
• and
• a second control circuit for comparing voltage at a second node, to which a second variable resistor is connected, with voltage at the first node, and for outputting a second control code controlling a dummy variable resistor that supplies electric current to the second node and is the same as the first variable resistor,
• wherein the first variable resistor and the dummy variable resistor are calibrated in response to the first control code, and at the same time the second variable resistor is calibrated to have the same resistance as that of the external resistor in response to the second control code, and
• the active termination resistor is calibrated to have the same resistance as that of the external resistor in response to the first control code and/or the second control code.

A circuit for calibrating an active termination resistor to have the same resistance as that of an external resistor, the circuit comprising:

• a first node to which the external resistor and a first variable resistor are connected;
• a first control code generation circuit for comparing voltage at the first node with a reference voltage, and for outputting a first control code corresponding to the comparison result;
• a second node to which a dummy variable resistor, which has the same resistance as that of the first variable resistor, and a second variable resistor are connected;
• and
• a second control code generation circuit for comparing voltage at the first node with voltage at the second node, and for outputting a second control code corresponding to the comparison result,
• wherein the first variable resistor and the dummy variable resistor are calibrated in response to the first control code, and at the same time the second variable resistor is calibrated to have the same resistance as that of the external resistor in response to the second control code, and
• the active termination resistor is calibrated to have the same resistance as that of the external resistor in response to the first control code and/or the second control code.

A memory device comprising:

• a calibrating circuit for outputting first and second control codes;
• a shifter block for multiplexing the first and second control codes in response to a selection signal, and for outputting control codes controlling an active termination resistor;
• and
• variable resistor units for calibrating the active termination resistor to have the same resistance as that of an external resistor connected to the calibrating circuit in response to the control codes,
• wherein the calibrating circuit comprises:
• a first node connected to the external resistor and a first variable resistor;
• a first control code generation circuit for comparing voltage at the first node and a reference voltage, and for outputting the first control code corresponding to the comparison result;
• a second node connected to a dummy variable resistor, which is the same as the first variable resistor, and a second variable resistor;
• and
• a second control code generation circuit for comparing voltage of the first node and voltage at the second node, and for outputting the second control code corresponding to the comparison result,
• wherein the first variable resistor and the dummy variable resistor are calibrated to have the same resistance as that of the external resistor in response to the first control code, and at the same time the second variable resistor is calibrated to have the same resistance as that of the external resistor in response to the second control code.