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

摘要

A circuit and method for calibrating an active termination resistor irrespective of changes in process, voltage, or temperature is provided. The method includes the steps of (a) calibrating a first variable resistor to have the same resistance as that of an external resistor; (b) at the same time calibrating a second variable resistor to have the same resistance as that of the first variable resistor; and (c) calibrating the active termination resistor to have the same resistance as that of the external resistor. The step of calibrating the first variable resistor to have the same resistance as that of the external resistor is in response to a first control code, and at the same time the step of calibrating the second variable resistor to have the same resistance as that of the first variable resistor is in response to a second control code. The first control code is generated to correspond to a comparison value in resistance of the first variable resistor with the external resistor, and the second control code is generated to correspond to a comparison value in resistance of the first variable resistor with the second variable resistor. During step (a), the resistance of the first variable resistor and the resistance of the second variable resistor increase or decrease at the same time.