A circuit that includes a current source and a current comparator is disclosed. The current source is connected to a resistive memory cell to generate a driving current thereto. The current comparator has a sensing node connected to the current source and the resistive memory cell to sense an injection current injected to the current comparator through the sensing node, wherein when a resistive state of the resistive memory cell switches such that the current comparator determines that an amount of the injection current increases to exceed or decreases to reach threshold value, the current comparator turns off the current source.