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AN-632
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
INTRODUCTION
This application note describes how to use the AD9951
direct digital synthesizer (DDS) as an agile reference
clock generator for the ADN2812 continuous-rate clock
and data recovery (CDR) device.
In a typical application, the ADN2812 will automatically
lock to any incoming serial NRZ data stream between
10 Mb/s and 2.7 Gb/s without needing a reference clock
as an acquisition aid or any programming for a specic
data rate or range of data rates. This is ideal for protocol
agnostic line cards that have multiple channels receiving
different protocols at different data rates (Figure 1).
Provisioning Data Rates Using the AD9951 DDS as an Agile
Reference Clock for the ADN2812 Continuous-Rate CDR
By Mike Hummel and Kevin Buckley
However, the ADN2812 has an optional mode where a ref-
erence clock can be supplied in order to limit the ADN2812
to lock to a specic data rate. For example, in a DWDM
system there can be 16 different channels carrying 16 dif-
ferent protocols. The provider may want to limit the rate
on any particular channel for billing purposes by setting
up the ADN2812 to lock to only the data rate being billed
to the customer on that particular channel.
The AD9951 DDS with the ADN2812 CDR provides a
simple, space-saving solution for a frequency agile
receiver that needs to lock to a wide range of specic
data rates on protocol agnostic line cards.
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Figure 1. WDM Transponder Block Diagram
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