Integrated circuit devices and methods of operating integrated circuit devices are useful in impedance adjustment. Integrated circuit devices include a signal driver circuit having an output node, a voltage node, and a first termination device and a second termination device connected in parallel between the voltage node and the output node. The first termination device and the second termination device each have a particular configuration of switchable resistances, and different strengths. Methods include connecting a node of the integrated circuit device to a first voltage node through a reference resistance, connecting the node to a second voltage node through a termination device, adjusting a resistance value of the termination device and comparing a resulting voltage level to a reference voltage. The reference voltage has a voltage level different than half-way between a voltage level of the first voltage node and a voltage level of the second voltage node.