1. Custom Circuit Group, Apple, Cupertino, CA, USA
2. Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Seoul National University, Seoul, South Korea
3. School of Electronic Engineering, Department of Intelligent Semiconductors, Soongsil University, Seoul, South Korea
4. Department of Electrical and Computer Engineering, College of Information and Communication Engineering, Sungkyunkwan University, Suwon, South Korea
5. Department of Electrical Engineering, Columbia University, New York, NY, USA