Design of Cmos Receivers for Parallel Optical Interconnects

The growing demand for high-bandwidth communication between integrated circuits calls for large numbers of high-speed inputs and outputs (IOs) per chip. IO data rates have increased to the point where electrical signaling is now limited by the channel properties. In order to achieve multi-Gb/s data rates, complex designs that equalize the channel are necessary. Using optics for chip-to-chip interconnections is promising since the optical channel dispersion and cross-talk are small. In this work we demonstrate the possibility of building small and low-power optical receivers that facilitate large numbers of IOs. A new double sampling/integrating front-end is proposed and implemented. Unlike prior designs, this receiver removes the need for a gain stage that runs at the data rate, making it suitable for low-power implementations. This front-end allows a timedivision multiplexing technique to support very high data rates. The dynamic range of the integrating input node can be improved by a decision-directed common-mode control loop, which reduces the required supply voltage. The synchronized receive clock can be generated in many ways. While the standard oversampled clock recovery is possible, it needs extra clock phases in the middle of main data samples. In order to reduce the power, a baud rate clock recovery technique is proposed and implemented as part of a transceiver array test-chip. The resulting transceiver consumes less than 150mW per channel at 5.0Gb/s in a 0.25μm CMOS technology. If projected to a 90nm CMOS technology, 15Gb/s data rate and 30mW power per IO are possible, which allow more than 10Tb/s chip-to-chip bandwidth, with up to one thousand IOs per chip. iv Acknowledgements During my graduate studies at Stanford University, I had the privilege of learning from the best teachers and receiving support from the most caring friends. This work would not have been possible without any of the two. First of all, I would like to thank my Ph.D. advisor Professor Mark Horowitz. Mark’s knowledge, vision and personality make him the greatest advisor and teacher one could ever wish for. Every single meeting with Mark helped me to go another step forward in my research, and motivated me to learn more. Mark’s enthusiasm and care were the driving forces for the creation of new ideas in this work. He also effectively helped me to improve my public speaking and writing skills. I sincerely thank him for his kindness and patience. I gratefully acknowledge my co-advisor Professor David Miller for his invaluable advice and help. Professor Miller was the one who initiated this research and inspired this project as a collaboration between the two research groups. Working in his laboratory and with his students was a great opportunity for me to expand my knowledge to the area of photonics. I also would like to thank him for being a member of my oral defence and reading committees. I would like to extend my gratitude to Professor Bruce Wooley for his advice, encouragements and help throughout my years at Stanford, and for serving as a member of my oral defence and reading committees. The faculty of the Department of Electrical Engineering at Stanford are among the most brilliant teachers in the world and I had the opportunity of learning from many of them. Particularly, I would like to express my gratitude to Professor Fabian Pease, chair of my orals committee and Professor Tom Lee, who both helped me v during my first year at Stanford. With no doubt, a great aspect of being one of Mark’s students was to be in a friendly and highly cooperative research group. I would like to thank Samuel Palermo, Hae-Chang Lee and Elad Alon for their help in building my second testchip. I also thank Jaeha Kim and Dean Liu for their technical help and for answering my numerous questions. I am thankful for technical discussions with Vladimir Stojanovic, Ken Mai, Ron Ho, Kun-Yung Chang, Ken Yang and Bill Ellersik. I appreciate the friendship of other former and current students in the Horowitz group, Bennett Wilburn, Michal Smulski, Evelina Yeung, Gu-Yeon Wei, Amin Firoozshahian, Francois Labonte, Alex Solomatnikov, Vicky Wong, and Dinesh Patil. The members of Professor Miller’s group greatly helped me in the optical testing of my chips. I would like to thank Aparna Bhatnagar, Gordon Keeler, Noah Helman and Diwakar Agarwal for the integration of optical devices, lab set-ups and technical discussions. This work was possible with the generous support from National Semiconductor, Vitesse Semiconductor, DARPA and MRCO IFC. I also would like to thank CSL administrators, Teresa Lynn, Penny Chumley, and Taru Fisher, as well as the CIS staff members and computer administrators for creating an amazing work environment for us. I sincerely thank CIS former students Hirad Samavati, Joel Dawson and Lalit Nathawad, who took the responsibility of the National tape out. The highly academic environment at Sharif University of Technology helped me to build the required background in engineering and inspired me to pursue my graduate studies abroad. I sincerely thank Professor Sharif-Bakhtiyar, Professor Fotovat, and Professor Jahanbeglo for the advice, encouragements and remarkable teachings. My first exposure to science and engineering goes back to my high-school years attending Farzanegan, with the most dedicated and caring teachers. I would like to thank, Ms. Poorsaeed, Mr. Niusha, Mr. Helli, Ms. Mokhtari, Ms. Rohani, Mr. Kazemi, and Mrs Haerizadeh. I would like to thank my friends Valeria Bertacco, Vace Shakoori, Sadaf Safaii, Fatemeh Jalayer, Yasamin Mostofi, Mahmood Reza Kasnavi, Dara Ghahremani, Farid Nemati, Ali Hajimiri, Ramin Farjad-rad, Amy Droitcour, Ardavan Maleki, Mina vi Matin, Parisa Gholami, Arjang Hassibi and Nogol Rashidi for making Stanford a fun place to live and work. I also thank Mahmood Kalantar and Arja Nikmo for their kindness and friendship. I sincerely thank my best friend Kaveh Hosseini who helped me to go forward in every stage of my graduate studies. His encouragements and friendship brought peace and happiness to my life. My brother Sohrab has been an amazing mentor. He always inspired and motivated me to do my best. All these years, my lovely sisters Maryam and Mitra eased the hardship of being away from home by their love, beautiful gifts and letters. My deepest love and gratitude go to these three. I dedicate this thesis to my parents, Mr. Akbar Emami-Neyestanak and Mrs. Khatoon Hadavi-Neyestanaki for their lifelong efforts to provide the best for me. I deeply appreciate their endless love, support and sacrifices. At the end, I cherish the memory of Masoomeh Hadavi and Zhila Asghari.