Patent ID: 7952382
Filing Date: 2011-05-31
Classification: G11C,H03K

Abstract:
1. An impedance calibration circuit, comprising: a driving circuit comprising a plurality of legs in parallel, each leg including a switching element and a resistance element in series, a resistance element of at least one of the legs being a variable resistance, wherein an impedance of the legs is varied according to a code signal controlling the switching elements of the legs in order to calibrate the impedance, wherein the driving circuit compares an impedance of the legs to an input/output impedance of an external device and provides the result of the comparison as a calibration voltage, and wherein the variable resistance of the resistance element of at least one of the legs can be controllable adjusted independent of the code signal to vary the impedance of the legs; and a comparing circuit comparing the calibration voltage to a reference voltage in order to provide the code signal for calibrating an impedance corresponding to output data with the input/output impedance of the external device, wherein the variable resistance has a resistance value that is varied independently of the impedance determined following the code value of the code signal.