There is provided a reference voltage generator for providing an adaptive voltage. The reference voltage generator includes a steady current source and a PMOS transistor and an NMOS transistor cascaded to each other. A reference voltage provided by the reference voltage generator is determined by gate-source voltages of the PMOS transistor and the NMOS transistor. As said gate-source voltages vary with the temperature and manufacturing process, the reference voltage forms a self-adaptive voltage.