With the exponential growth of the number of Internet nodes, the
volume of the data transported on the backbone has increased with
the same trend. The load of the global Internet backbone will soon
increase to tens of terabits per second. This indicates that the backbone
bandwidth requirements will increase by a factor of 50 to 100 every seven
years.
Transportation of such high volumes of data requires suitable media
with low loss and high bandwidth. Among the available transmission
media, optical fibers achieve the best performance in terms of loss and
bandwidth.
High-speed data can be transported over hundreds of kilometers of
single-mode fiber without significant loss in signal integrity. These fibers
progressively benefit from reduction of cost and improvement of performance.
Meanwhile, the electronic interfaces used in an optical network are
not capable of exploiting the ultimate bandwidth of the fiber, limiting
the throughput of the network. Different solutions at both the system
and the circuit levels have been proposed to increase the data rate of
the backbone.
System-level solutions are based on the utilization of wave-division
multiplexing (WDM), using different colors of light to transmit several
sequences simultaneously. In parallel with that, a great deal of
effort has been put into increasing the operating rate of the electronic
transceivers using highly-developed fabrication processes and novel circuit
techniques.
The design of the clock and data recovery (CDR) circuit is the most
challenging part of building a high-speed optical transceiver because of
the complexity of this block. In this book, the design and experimental
results of two CDR circuits are described. Both the circuits achieve a
high operating speed by employing the concept of “half rate”, meaning
that the clock frequency is half the data rate. Furthermore, broadband
circuit techniques including wideband amplification and high-speed
matched filtering are described in this book.
The two CDR circuits benefit from two major techniques for phase
detection, namely linear and binary. The design of the linear phase detector
is based on a new technique that allows a fast speed and low power
consumption because of its simplicity. The new binary phase/frequency
detector provides a wide capture range and a phase error signal that
is only revalidated at data transitions. Furthermore, the design of the
CDR circuits involves utilization of two major types of voltage-controlled
oscillators, which are ring and LC-tuned. The ring oscillator described
in this work achieves a wide tuning range and low power consumption.
The LC oscillator benefits from a new topology that provides multiple
phases with low jitter.