Patent ID: 7382152

Claim:
An input/output interface circuit of an integrated circuit, comprising: a plurality of transistor pairs; an input/output terminal being connected to a connection point of each transistor pair of the plurality of transistor pairs; and a controller controlling switching of each transistor of the plurality of transistor pairs to constitute an output buffer in output mode and a termination circuit in input mode, and controlling output impedance of the output buffer and load impedance of the termination circuit to be a predetermined value, wherein said plurality of transistor pairs constitute a driver including a primary driver and a secondary driver, and the flue controller comprises a drive controller, controlling switching of each transistor of the driver, and an impedance controller outputting an impedance control signal to the drive controller which generates a control signal for controlling said secondary driver and for controlling impedance of the driver based on reference resistance, wherein said primary driver is controlled other than by said impedance controller, and wherein the plurality of transistor pairs include a plurality of transistor sets, each set consisting of two transistor pairs including two first transistors and two second transistors, each having the same on-resistance, in which: in input mode, one of two transistor pairs of a first set is turned on and the first transistor and/or the second transistor of a second, or later set are selectively turned on; and in output mode, two first transistors or two second transistors of the first set are turned on and the first transistor or the second transistor of the second or later set is selectively turned on.