A memory device includes a memory array, an I/O circuit for accessing the memory array, and a tracking circuit. The tracking circuit includes a dummy bit line, a first tracking cell including a first NMOS transistor, the first tracking cell being coupled to receive a control signal and also coupled to the dummy bit line through the first NMOS transistor, and a second tracking cell including a second NMOS transistor, the second tracking cell being coupled to receive the control signal and also coupled to the dummy bit line through the second NMOS transistor, a gate of the second NMOS transistor being coupled to the dummy bit line. The memory device also includes a control circuit coupled to the dummy bit line for generating a clock signal for the I/O circuit.