SC357 Computercom Interconnects: Circuits and Equalization Methods for Short Reach Power-Efficient Optical and Electrical Links

Monday, 18 March 2013
9:00 - 12:00

Instructor: Alexander Rylyakov; IBM T.J. Watson Research Center, USA

Level: Advanced Beginner (basic understanding of topic is necessary to follow course material)

Description:
 Unlike telecom or datacom (where optics dominates), computercom interconnect applications is the area where optical and electrical I/O solutions are often in direct competition on all main performance parameters: reach, bandwidth, power efficiency, density and cost.  To achieve the highest level of performance, both types of links require highly specialized front-end circuits and equalization methods.
 
The main focus of the course will be on circuits for VCSEL-based multi-mode optical links.  All key circuit topologies and performance parameters will be compared to corresponding wireline transceiver solutions. For completeness, we will also briefly discuss circuits for Silicon Photonics applications.
 
We will start with outlining the basics of channel properties and communication techniques. We will then review the most common front-end I/O circuit topologies used in both optical and electrical short reach interconnects and compare their overall efficiencies. Typical transmitter and receiver architectures for both electrical and optical links will be presented, with discussion of basic functionality and performance requirements for each of the building blocks.  We will outline the similarities as well as the differences between the key front-end components (e.g., VCSEL driver vs wireline driver vs Silicon Photonic modulator driver), and their effect on the overall link performance. The review will also include a brief discussion of the high-speed digital MUX/DEMUX (serializer/deserializer) circuits and the CDR (clock and data recovery) function. We will compare the most commonly used SiGe bipolar and CMOS technologies in terms of performance, power dissipation, area and cost. Several optical and electrical full link power efficiency examples will be presented and discussed.
 
Electrical links have to employ heavy-duty equalization techniques due to severe bandwidth limitations of wireline channels, but optical solutions can also greatly benefit from equalization, even at short reach. We will discuss the most commonly used equalization methods:

• continuous-time linear equalizer (CTLE, often used on both sides of the link)
• feed-forward equalizer (FFE, typically employed in the transmitter pre-emphasis)
• decision-feedback equalizer (DFE, commonly present in the receiver)

High-level descriptions of several topologies of FFE transmitters and DFE receivers will be presented, together with a discussion of tradeoffs involved when selecting one equalizer over another, or using both. We will conclude with discussion of several recently published results demonstrating the dramatic benefits of equalization for optical links.

Benefits:
 This course should enable you to:

• Outline overall transceiver architectures of typical wireline and optical short reach  links
• Explain functionality and performance requirements of all key front-end I/O building blocks
• Evaluate and compare the efficiencies of wireline and optical short reach interconnects
• Compare SiGe bipolar and CMOS circuits for short reach optical and electrical links
• Understand and compare equalization techniques (CTLE, FFE, DFE)
• Discuss benefits and tradeoffs of equalization
• Make an educated choice between an optical and electrical solution for short reach interconnect

Audience:
This course is for anyone interested in learning the basic transmitter and receiver circuit architectures for both optical and electrical short reach interconnects. The course will help gain the insight into the main tradeoffs involved in choosing between the optical and electrical links, as well as the integrated circuit topologies and technologies used in the transceiver circuits. The overview of advanced equalization techniques will be also of interest to audience already familiar with the basics of short reach interconnect.

Instructor Biography:

 Alexander Rylyakov received the M.S. degree in physics from Moscow Institute of Physics and Technology in 1989 and the Ph.D. degree in physics from State University of New York at Stony Brook in 1997, where he worked on the design and testing of superconductor integrated circuits based on Josephson junctions.  In 1999 he joined the IBM T.J. Watson Research Center as a research staff member, working on the design and testing of high-speed digital and mixed-signal communication circuits for optical and channel-limited wireline communications. Many of those circuits, implemented in various generations of CMOS and SiGe bipolar, are now used in IBM products and several of them have established performance records in their respective technologies. Dr. Rylyakov's current research interests are in the areas of digital phase-locked loops for communication and microprocessor clocking, high-speed low power transceivers and equalization for wireline and optical communication, and integrated circuits for silicon photonics. He has published over 80 papers and has received 10 patents.