1. Department of Electrical Engineering, Hosei University, Kajinocho, Koganei, Tokyo 184, Japan
2. Sharp Corporation, LSI Research and Development, IC Division, Ichinomotocho, Tenri, Nara 632, Japan
3. Rigaku Corporation, Matsubara, Akishima, Tokyo 196, Japan
4. Rigaku Industrial Corporation, Akaoji, Takatsuki, Osaka 569, Japan