Data Retiming
Phase-Locked Loop
a
AD805*
CLOCK RECOVERY AND
FEATURES
DATA RETIMING APPLICATION
155 Mbps Clock Recovery and Data Retiming
Permits CCITT G.958 Type A Jitter Tolerance
Permits CCITT G.958 Type B Jitter Transfer
Random Jitter: 0.6؇ rms
Pattern Jitter: Virtually Eliminated
Jitter Peaking: Fundamentally None
Acquisition: 30 Bit Periods
Accepts NRZ Data without Preamble
Single Supply Operation: –5.2 V or +5 V
10 KH ECL Compatible
VOLTAGE
CONTROLLED
PHASE
LOOP
FILTER
PHASE
DETECTOR
DATA
INPUT
GAIN
SHIFTER
RETIMING
MODULE
VCXO
(EXTERNAL)
RECOVERED
CLOCK
RETIMED
DATA
AD805
PRODUCT DESCRIPTION
The AD805 is a data retiming phase-locked loop designed for
use with a Voltage-Controlled Crystal Oscillator (VCXO) to
perform clock recovery and data retiming on Nonreturn to Zero
(NRZ) data. The circuit provides clock recovery and data
retiming on standard telecommunications STS-3 or STM-1
data (155.52 Mbps). A Vectron C0-434Y Series VCXO circuit
is used with the AD805 for specification purposes. Similar
circuit performance can be obtained using other commercially
available VCXO circuits. The AD805-VCXO circuit used for
clock recovery and data retiming can also be used for large
factor frequency multiplication.
phase shifter, phase detector, and loop filter, act to align input
data phase errors to the stable recovered clock provided by the
VCXO. The range of the voltage-controlled phase shifter, at
least 2 Unit Intervals (UI), and the bandwidth of this loop, at
roughly 3 MHz, provide the circuit with its wideband jitter
tolerance characteristic.
The circuit can acquire lock to input data very quickly, within
44 bit periods, due to the accuracy of the VCXO and the action
of the data retiming loop. Typical integrated second-order PLLs
take at least several thousand bit periods to acquire lock. This is
due to their having a wide tuning range VCO. Decreasing the
loop damping of a traditional second-order PLL shortens the
length of the circuit’s acquisition time, but at the expense of
greater jitter peaking.
The AD805-VCXO circuit meets or exceeds CCITT G.958
regenerator specifications for STM-I Type A jitter tolerance and
STM-1 Type B jitter transfer. The simultaneous Type A, wide-
band jitter tolerance and Type B, narrow-band jitter transfer
allows the use of the AD805-VCXO circuit in a regenerative
application to overcome optical line system interworking limit-
ations based on signal retiming using Type A passive tuned
device technology such as Surface-Acoustic-Wave (SAW) or
dielectric resonator filters, with Type B active devices such as
Phase-Locked Loops (PLLs).
The AD805-VCXO circuit is a second- order PLL that has no
jitter peaking. The zero used to stabilize the control loop of the
traditional second-order PLL effects the closed-loop transfer
function, causing jitter peaking in the jitter transfer function. In
the AD805-VCXO circuit, the zero needed to stabilize the loop
is implemented in the feedback path, in the voltage-controlled
phase shifter. Placing the zero in the feedback path results in
fundamentally no jitter peaking since the zero is absent from the
closed-loop transfer function.
The circuit VCXO provides a stable and accurate clock fre-
quency signal with or without input data. The AD805 works
with the VCXO to dynamically adjust the recovered clock fre-
quency to the frequency associated with the input data. This
frequency control loop tracks any low frequency component of
jitter on the input data. Since the circuit uses the VCXO for
clock recovery, it has a high Q for excellent wideband jitter at-
tenuation. The jitter transfer characteristic of the circuit is with-
in the jitter transfer requirements for a CCITT G.958 STM-1
Type B regenerator, which has a corner frequency of 30 kHz.
Output jitter, determined primarily by the VCXO, is a very low
0.6° rms. Jitter due to variations in input data density, pattern
jitter, is virtually eliminated in the circuit due to the AD805’s
patented phase detector.
The data retiming loop of the AD805 can be used with a passive
tuned circuit (155.52 MHz) such as a bandpass or a SAW filter
for clock recovery and data retiming. The data retiming loop
acts to servo the phase of the input data to the phase of the
recovered clock from the passive tuned circuit in this type of
application (see APPLICATIONS).
The AD805 overcomes the higher frequency jitter tolerance
limitations associated with traditional high Q, PLL based clock
and data recovery circuits through the use of its data retiming
loop. This loop, made up of the AD805’s voltage-controlled
The AD805 uses 10 KH ECL levels and consumes 375 mW
from a +5 V or a –5.2 V supply. The device is specified for
operation over the industrial temperature range of –40°C to
+85°C and is available in a 20-pin plastic DIP.
*Protected by U.S. Patent No. 5,036,298
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 1996
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