Patent ID: 7911223

Claim:
A calibration circuit of an on-die termination (ODT) device, comprising: a reference voltage generating circuit configured to combine a constant voltage generated from a bandgap circuit and a divided voltage generated by dividing a power supply voltage with a voltage division circuit and output the combination as a reference voltage at an intervening node between the bandgap circuit and the voltage division circuit; a code generating unit configured to generate pull-up calibration codes in response to a voltage of a calibration node connected to an external resistor and the reference voltage; and a pull-up calibration resistor unit configured to pull up the calibration node in response to the pull-up calibration codes wherein: the pull-up calibration resistor unit is calibrated to have a resistance equal to that of the external resistance and the reference voltage is substantially equal to a half of the power supply voltage when the power supply voltage is equal to a predetermined voltage; the pull-up calibration resistor unit is calibrated to have a resistance higher than that of the external resistance and the reference voltage is lower than a half of the power supply voltage when the power supply voltage is higher than the predetermined voltage; and the pull-up calibration resistor unit is calibrated to have a resistance lower than that of the external resistance and the reference voltage is higher than a half of the power supply voltage when the power supply voltage is lower than the predetermined voltage.