1. Department of Engineering and System Science; National Tsing Hua University; Hsinchu 30013 Taiwan
2. Department of Electronics Engineering; National Chiao Tung University; Hsinchu 30010 Taiwan
3. Department of Electronic Engineering; Xiamen University; Xiamen 361005 P.R. China
4. Department of Mechatronic Engineering; National Taiwan Normal University; Taipei 10610 Taiwan