1. Research and Development Department, Samco Inc. 1 , 94 Tanakamiya-cho, Takeda, Fusimi-ku, Kyoto 612-8444, Japan
2. Department of Electronics, Kyoto Institute of Technology 2 , Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
3. Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology 3 , Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan