Brief Introduction of High-Speed Circuits for Optical Communication Systems Zheng Wang Instructor: Dr. Liu

Outline  Introduction  System Overview  TIA design  Limiter Design  Frequency Acquisition  CDR Design  Prospects

Global Internet Backbone Growth ( data released by research firm TeleGeography in 2002 )

SerDes Transceivers SerDes Transceivers (high–speed, full–duplex, serializer/deserializer)

Dedicated line broadband speeds  T megabits per second (24 DS0 lines) Ave. cost $1,200./mo.  T megabits per second (28 T1s) Ave. cost $28,000./mo.  OC megabits per second (100 T1s) Ave. cost $49,000./mo.  OC gigabits per seconds (4 OC12s) no est. price available  OC gigabits per second (4 OC48s) no est. price available

Optical Communication System

TIA (Transimpedance Amplifier )  Transimpedance Gain  Bandwidth & Power Dissipation  Voltage Headroom  Input & Output Impedance

TIA Circuit (a)  Gain = ?  Noise contributed by M1 rises at high frequency  Poor performance at low voltage supply

TIA Circuit (b)  Gain = R F  Value of R F can be maximized because it does not limit the voltage headroom

TIA Building Block  Intel LXT Power Supply 3.3V. Power dissipation less than 160mW  high optical input sensitivity (as good as -20dBm). Suitable for long-haul transmissions. Up to 10.7Gbps speed.

Limiter Design  Voltage Gain  Bandwidth (Low End & High End)  Phase Response  DC Offset

Two Limiter Topologies

Limiter Design by MOSFET  With ideal inductors, bandwidth is increased by 82%  With actual inductors, bandwidth is increased by 50%  But inductors consume substantial area

CDR Design ( CDR Design (clock-and-data recovery)  Jitter Generation, Transfer, and Tolerance  Frequency Capture Range  Response to Long Runs  Flip-flop and Oscillator Speed

Typical CDR Architecture

Frequency Acquisition  Capture range is typically a few percent.  VCO center frequency can vary substantially with process and temperature.  Must drive the VCO frequency toward the data rate before phase-locking can occur

Definition of Jitter  Synchronous networks such as the Synchronous Digital Hierarchy (SDH) and the Synchronous Optical NETwork (SONET) rely on highly accurate and stable synchronization to process data in and out of network elements.  Jitter is used to describe short term, non- cumulative variations of the significant instants of a digital signal from their ideal positions in time

CDR Jitter Generation  Jitter Generation: Peak-to-peak jitter produced by CDR circuit itself. Must typically remain below 0.1dB. To eliminate the jitter, there are several ways. (reference: Cheung, Jonathan, “Low Jitter Phase-Locked Loop”)

Prospects of CMOS Technology  The transit frequency of 0.13-um NMOS devices exceeds 100 GHz.  As with RF circuits, optical communication circuits can greatly benefit from CMOS technology.  The cost and integration advantages of CMOS manifest themselves in:  - Wave-Division Multiplexing Systems  - Multiple Transceivers for Bundle of Fibers  - Highly-Integrated Transceivers  CMOS at 40 Gb/s? Why Not?

Recommended Book   “Design of Integrated Circuits for Optical Communications” by Behzad RazaviBehzad Razavi   List Price: $   Half.com: $56.35 Half.com:

Reference Paper  Cheung, Jonathan, “Low Jitter Phase-Locked Loop”  “LXT16865 Transimpedance Amplifier (TIA)”  Mauldin, Alan, “Global Internet Backbone Growth Slows Dramatically,” October 16, 2002 October 21,  Schmitt, Nicolas, “Jitter Measurements of Agilent Technologies OC-48 Optical Transceivers using the OmniBER718” ments2.pdf ments2.pdf  “T1, T3, OC3, OC12, OC48 and OC192 Research Information”

Thank You for your time Questions?