An integrated circuit includes a plurality of resistivity changing memory cells and at least one resistivity changing reference cell; a voltage comparator including a first and second input terminals; a signal line connected to the memory cells, the reference cell, and the second input terminal; and a switching element connecting the first input terminal to the second input terminal. A method of operating the integrated circuit includes closing the switching element; supplying a first voltage to the first input terminal via the signal line and the switching element; opening the switching element; supplying a second voltage to the second input terminal via the signal line; and comparing the first and second voltages using the voltage comparator, wherein the first voltage represents a memory state of a memory cell, and the second voltage is a reference voltage which represents a memory state of a reference cell, or vice versa.