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Clock Recovery and Data Retiming

AD808

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1998

FEATURES

Meets CCITT G.958 Requirements

for STM-4 Regenerator—Type A

Meets Bellcore TR-NWT-000253 Requirements for OC-12

Output Jitter: 2.5 Degrees RMS

622 Mbps Clock Recovery and Data Retiming

Accepts NRZ Data, No Preamble Required

Phase-Locked Loop Type Clock Recovery—

No Crystal Required

Quantizer Sensitivity: 4 mV

Level Detect Range: 10 mV to 40 mV, Programmable

Single Supply Operation: +5 V or –5.2 V

Low Power: 400 mW

10 KH ECL/PECL Compatible Output

Package: 16-Lead Narrow 150 mil SOIC

frequency acquisition without false lock. This eliminates a reli-

ance on external components such as a crystal or a SAW filter,

to aid frequency acquisition.

The AD808 acquires frequency and phase lock on input data

using two control loops that work without requiring external

control. The frequency acquisition control loop initially acquires

the frequency of the input data, acquiring frequency lock on

random or scrambled data without the need for a preamble. At

frequency lock, the frequency error is zero and the frequency

detector has no further effect. The phase acquisition control

loop then works to ensure that the output phase tracks the input

phase. A patented phase detector has virtually eliminated pat-

tern jitter throughout the AD808.

The device VCO uses a ring oscillator architecture and patented

low noise design techniques. Jitter is 2.5 degrees rms. This low

jitter results from using a fully differential signal architecture,

Power Supply Rejection Ratio circuitry and a dielectrically

isolated process that provides immunity from extraneous signals

on the IC. The device can withstand hundreds of millivolts of

power supply noise without an effect on jitter performance.

The user sets the jitter peaking and acquisition time of the PLL

by choosing a damping factor capacitor whose value determines

loop damping. CCITT G.958 Type A jitter transfer require-

ments can easily be met with a damping factor of 5 or greater.

Device design guarantees that the clock output frequency will

drift by less than 20% in the absence of input data transitions.

output frequency to the VCO center frequency.

The AD808 consumes 400 mW and operates from a single

power supply at either +5 V or –5.2 V.

FUNCTIONAL BLOCK DIAGRAM

SIGNAL

LEVEL

DETECTOR

COMPENSATING

ZERO

VCO

RETIMING

DEVICE

LOOP

FILTER

DET

PIN

NIN

THRADJ

SDOUT

CLKOUTP

CLKOUTN

DATAOUTP

DATAOUTN

LEVEL

DETECT

COMPARATOR/

BUFFER

AD808

PHASE-LOCKED LOOP

CF1

CF2

QUANTIZER

PRODUCT DESCRIPTION

The AD808 provides the receiver functions of data quantiza-

tion, signal level detect, clock recovery and data retiming for

622 Mbps NRZ data. The device, together with a PIN

diode/preamplifier combination, can be used for a highly inte-

grated, low cost, low power SONET OC-12 or SDH STM-4

fiber optic receiver.

The receiver front end signal level detect circuit indicates when

the input signal level has fallen below a user adjustable thresh-

old. The threshold is set with a single external resistor. The

signal level detect circuit 3 dB optical hysteresis prevents chatter

at the signal level detect output.

The PLL has a factory trimmed VCO center frequency and a

frequency acquisition control loop that combine to guarantee