Clock Recovery and Data Retiming
Phase-Locked Loop
a
AD800/AD802*
FUNCTIO NAL BLO CK D IAGRAM
FEATURES
Standard Products
C
D
44.736 Mbps—DS-3
51.84 Mbps—STS-1
155.52 Mbps—STS-3 or STM-1
Accepts NRZ Data, No Pream ble Required
Recovered Clock and Retim ed Data Outputs
Phase-Locked Loop Type Clock Recovery—No Crystal
Required
Random J itter: 20؇ Peak-to-Peak
Pattern J itter: Virtually Elim inated
10KH ECL Com patible
COMPENSATING
ZERO
LOOP
DATA
INPUT
Ø
DET
∑
FILTER
VCO
RECOVERED
CLOCK
f
OUTPUT
DET
RETIMED
DATA
OUTPUT
RETIMING
DEVICE
Single Supply Operation: –5.2 V or +5 V
Wide Operating Tem perature Range: –40؇C to +85؇C
AD800/AD802
FRAC
OUTPUT
P RO D UCT D ESCRIP TIO N
During the process of acquisition the frequency detector
provides a Frequency Acquisition (FRAC) signal which
indicates that the device has not yet locked onto the input data.
T his signal is a series of pulses which occur at the points of cycle
slip between the input data and the synthesized clock signal.
Once the circuit has acquired frequency lock no pulses occur at
the FRAC output.
T he AD800 and AD802 employ a second order phase-locked
loop architecture to perform clock recovery and data retiming
on Non-Return to Zero, NRZ, data. T his architecture is
capable of supporting data rates between 20 Mbps and 160
Mbps. T he products described here have been defined to work
with standard telecommunications bit rates. 45 Mbps DS-3 and
52 Mbps ST S-1 are supported by the AD800-45 and
AD800-52 respectively. 155 Mbps ST S-3 or ST M-1 are
supported by the AD802-155.
T he inclusion of a precisely trimmed VCO in the device
eliminates the need for external components for setting center
frequency, and the need for trimming of those components. T he
VCO provides a clock output within ±20% of the device center
frequency in the absence of input data.
Unlike other PLL-based clock recovery circuits, these devices
do not require a preamble or an external VCXO to lock onto
input data. T he circuit acquires frequency and phase lock using
two control loops. T he frequency acquisition control loop
initially acquires the clock frequency of the input data. T he
phase-lock loop then acquires the phase of the input data, and
ensures that the phase of the output signals track changes in the
phase of the input data. T he loop damping of the circuit is
dependent on the value of a user selected capacitor; this defines
jitter peaking performance and impacts acquisition time. T he
devices exhibit 0.08 dB jitter peaking, and acquire lock on
random or scrambled data within 4 × 105 bit periods when
using a damping factor of 5.
T he AD800 and AD802 exhibit virtually no pattern jitter, due
to the performance of the patented phase detector. T otal loop
jitter is 20° peak-to-peak. Jitter bandwidth is dictated by mask
programmable fractional loop bandwidth. T he AD800, used for
data rates < 90 Mbps, has been designed with a nominal loop
bandwidth of 0.1% of the center frequency. T he AD802, used
for data rates in excess of 90 Mbps, has a loop bandwidth of
0.08% of center frequency.
All of the devices operate with a single +5 V or –5.2 V supply.
*P r otected by U.S. P atent No. 5,027,085.
REV. B
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703
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