AD9551 Datasheet, PDF (1/40 Pages) Analog Devices – Multiservice Clock Generator

Multiservice Clock Generator
AD9551
FEATURES
Translation between any two standard network rates
Dual reference inputs and dual clock outputs
Pin programmable for standard network rate translation
SPI programmable for arbitrary rational rate translation
Output frequencies from 10 MHz to 900 MHz
Input frequencies from 19.44 MHz to 806 MHz
On-chip VCO
Meets OC-192 high band jitter generation requirement
Supports standard forward error correction (FEC) rates
Supports holdover operation
Supports hitless switchover and phase build-out (even with
unequal reference frequencies)
SPI-compatible 3-wire programming interface
Single supply (3.3 V)
APPLICATIONS
Multiservice switches
Multiservice routers
Exact network clock frequency translation
General-purpose frequency translation
GENERAL DESCRIPTION
The AD9551 accepts one or two reference input signals to synthe-
size one or two output signals. The AD9551 uses a fractional-N
PLL that precisely translates the reference frequency to the desired
output frequency. The input receivers and output drivers provide
both single-ended and differential operation.
Reference conditioning and switchover circuitry internally
synchronizes the two references so that if one reference fails,
there is virtually no phase perturbation at the output.
The AD9551 uses an external crystal and an internal DCXO to
provide for holdover operation. If both references fail, the device
maintains a steady output signal.
The AD9551 provides pin-selectable, preset divider values for
standard (and FEC adjusted) network frequencies. The pin-
selectable frequencies include any combination of 15 possible
input frequencies and 16 possible output frequencies. A SPI
interface provides further flexibility by making it possible to
program almost any rational input/output frequency ratio.
The AD9551 is a clock generator that employs fractional-N-based
phase-locked loops (PLL) using sigma-delta (Σ-Δ) modulators
(SDMs). The fractional frequency synthesis capability enables
the device to meet the frequency and feature requirements for
multiservice switch applications. The AD9551 precisely generates
a wide range of standard frequencies when using any one of those
same standard frequencies as a timing base (reference). The
primary challenge of this function is the precise generation of the
desired output frequency because even a slight output frequency
error can cause problems for downstream clocking circuits in
the form of bit or cycle slips. The requirement for exact frequency
translation in such applications necessitates the use of a frac-
tional-N-based PLL architecture with variable modulus.
BASIC BLOCK DIAGRAM
CRYSTAL
(26MHz)
REFA
REFERENCE
CONDITIONING
HOLDOVER
PLL
AND SWITCH-
LOOP
REFB
OVER
OUTPUT
CIRCUITRY
OUT1
OUT2
PIN-DEFINED AND SERIAL
PROGRAMMING
Figure 1.
AD9551
Rev. B
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
www.analog.com
Fax: [phone]
©2009 Analog Devices, Inc. All rights reserved.