1. School of Microelectronics, Hefei University of Technology, Hefei, Anhui 230601, P. R. China
2. College of Electrical Engineering, Anhui Polytechnic University, Wuhu, Anhui 241000, P. R. China
3. School of Integrated Circuits, Anhui University, Hefei, Anhui 230601, P. R. China