Photonic Network Communications, 6:1, 83±89, 2003
# 2003 Kluwer Academic Publishers. Manufactured in The Netherlands.
A Simulation Study on Clock Recovery of a Minimum
Kyung Gyu Chun*
Network Technology Lab., ETRI, Daejeon 305±350, S. Korea
Dae Young Kim
InfocomEngineering Department, ChungnamNational University, Daejeon 305±764, S. Korea
Received January 13, 2003; Revised and Accepted February 14, 2003
Abstract. Jitter and BER performance of non-linear clock recovery circuits are evaluated for a minimum bandwidth signal. To investigate the
effect of bandwidth in optical transmission, BER performance of MB810 and NRZ signals with various types of timing recovery circuits are
compared for a 40 Gbit/s optical link. Among the systems adopting non-linear timing recovery circuits, the MB810 signal employing an
absolute value recti®er shows superior performance. We show that timing recovery without a non-linear circuit is also possible, and compare its
BER performance with that of the others. Jitter performance of the fourth-law recti®er and that of the absolute-value recti®er is made for a
minimum bandwidth signal. The mathematical derivation of the timing wave is also carried out for the clock recovery of the fourth-law recti®er.
The result shows that the derived timing wave is expressed as a function of a pulse shape entering the timing path and the band-pass ®lter tuned
to the pulse repetition rate.
Keywords: timing recovery, minimum bandwidth, jitter, BER
Optical duobinary signals have been quite extensively
studied in high speed optical transmission systems
with rates such as 2.5 Gbit/s, 10 Gbit/s, and 40 Gbit/s.
It has been reported that an optical duobinary signal
has a strong optical dispersion tolerance due to
bandwidth limitation by the Nyquist frequency, and
that this nature results in an extended transmission
distance [1,2]. In addition, there is a strong carrier
tone in DC of the optical duobinary signal. This
suppressed optical carrier increases the stimulated
Brillouin scattering (SBS) threshold compared to a
conventional binary format .
As an alternative to the optical duobinary signal, we
consider a new minimum bandwidth signal which has
half of the original bandwidth is DC-free and has
limited run-length . The characteristics of the half
bandwidth and the DC-freedom of the minimum
bandwidth signal are very useful to achieve a high
capacity optical transmission system similar to a
duobinary system. The minimum bandwidth signal
was designed in such a way that the alternate sum
variation (ASV) and the digital sum variation (DSV)
in a line code are ®nite [5,6]. The ASV and DSV are
where I and J are arbitrary integers such that I < J and
is the output symbol sequence of the encoder.
In synchronous PAM, clock information can be
extracted by passing the incoming PAM signal into a
non-linear circuit followed by a narrow band pass