An integrated circuit includes a semiconductor substrate; a first node; a second node; and a first plurality of resistors, each in a first plurality of resistor units. Each of the first plurality of resistor units includes a first end connected to the first node, and a second end connected to the second node. The integrated circuit further includes a second plurality of resistors, each in a second plurality of resistor units. Each of the second plurality of resistor units includes a first end connected to the first node, and a second end connected to the second node. The first plurality of resistors is formed of a first material. The second plurality of resistors is formed of a second material different from the first material. The integrated circuit further includes a switch in one of the first and the second plurality of resistor units and serially connected to a resistor.