Agilent Technologies N4906B Serial BERT User manual

S1
Agilent N4906B Serial BERT
User’s Guide
Micro Precision Calibration, Inc.
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Grass Valley, CA 95949
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2Agilent N4906B Serial BERT, User’s Guide, October 2005
Important Notice
© Agilent Technologies, Inc. 2005
Revision
Revision 1.1, October 2005
Manual Part Number
N4906-91020
Printed in Germany
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Authors: t3 medien GmbH
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Contents
Agilent N4906B Serial BERT, User’s Guide, October 2005 3
Contents
Planning the Test 5
Introduction to the Serial BERT 6
Which Test is Appropriate? 9
Connecting the DUT 13
Setting up Patterns 19
User Patterns 24
Software-Generated PRBS 46
Hardware-Generated PRBS 49
Setting up the Pattern Generator 51
Input and Output Ports 52
Bit Rate 64
Trigger Output 69
Error Addition/Insertion 72
Pattern Alternation 76
Setting up the Error Detector 83
Inputs and Outputs 85
Clock Setup 91
Sampling Point Setup 98
Trigger and Aux Output 109
Pattern Synchronization 111
Error Accumulation 124
BER Location 127
Audio Signals 129
Advanced Analysis 131
Fast Eye Mask 138

Contents
4Agilent N4906B Serial BERT, User’s Guide, October 2005
Evaluating Results 147
Instantaneous Measurements 148
Accumulated Measurements 153
Eye Measurements 162
Solving Problems 165
Setup Problems 165
Measurement Problems 169
Other Messages 174
Customizing the Instrument 177
Restoring the System 177
Configuring the Instrument 179
Configuring the Touchscreen 183
Printing 187
File Management 190
Preset Instrument State 194
Self Test 195

Agilent N4906B Serial BERT, User’s Guide, October 2005 5
Planning the Test
The following topics provide some information that can help you in
planning tests with the Serial BERT:
• Introduction to the Serial BERT explains the basics of bit error
rates (BER) and BER testing with the Serial BERT.
• Which Test is Appropriate? provides you with some basic
information about the types of testing you can do with the
Serial BERT.
• Connecting the DUT tells you how you should connect your DUT to
the Serial BERT.

Planning the Test Introduction to the Serial BERT
6Agilent N4906B Serial BERT, User’s Guide, October 2005
Introduction to the Serial BERT
These topics explain some of the basics of BER, Serial BERT, and BER
testing with the Serial BERT.
Important Information about the Pattern Generator
Outputs
The pattern generator output ports must be terminated with 50 Ωif
they are not connected:
• Data Out
• Data Out
•ClockOut
•ClockOut
Termination of output ports improves the test performance.
Important Information Regarding Security
The Serial BERT is a PC-based instrument with a standard Windows
operating system. As such, it is subject to the same security protection
measures as any other PC.
See the Microsoft web site for more information regarding data
security:
http://www.microsoft.com/security/default.mspx
Every user must have administrator privileges to run the Serial BERT
firmware. Otherwise the firmware does not have access to the
instrument’s hardware.
It ist recommended that you create a recovery disk for the instrument.
See “How to Restore the Operating System” on page 178.
Note also that there is a recovery image on the hard disk. See the
Windows Help for instructions on restoring a recovery image.
Understanding BER
Bit error ratio (BER) is the most fundamental measure of system
performance. It is the ratio of the number of errored bits to the total
number of bits received.

Introduction to the Serial BERT Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 7
For example, 1 error in 1000 bits corresponds to a BER of 1/1000 or
1x10
–3. This would be displayed on the instrument as 1E-3. Refer to
the following table to familiarize yourself with how BERs are
displayed. Notice that smaller exponents correspond to higher BERs,
and larger exponents correspond to lower BERs.
Understanding the Serial BERT
The Agilent N4906B Serial BERT, also referred to as a Bit Error Ratio
Tester (BERT), is a powerful instrument that enables you to analyze
systems and components in the telecommunication and enterprise
communication industries. It is an essential tool for designing and
troubleshooting communications systems, high-speed integrated
circuits (ICs), and photonic components. Its intuitive operation and
leading edge performance will help you quickly verify error
performance.
The Agilent N4906B Serial BERT has the necessary capabilities to fully
characterize your digital device. The instrument provides:
•Excellentwaveformperformance
• Outstanding rise times
• A choice of logic family interfaces
• Easy object-oriented programming with the IVI-COM interface
• Remote commands similar to HP/Agilent 71603B
• A variety of ways in which to accumulate and view test results
• A collection of example patterns
• Convenient online documentation
• Automatic setup of optimum sampling point
Fraction Exponent Instrument Display
1/1 1 x 1001E+0
1/10 1 x 10–11E–1
1/100 1 x 10–21E–2
1/1000 1 x 10–31E–3
1/10,000 1 x 10–41E–4
1/100,000 1 x 10–51E–5
1/1,000,000 1 x 10–61E–6
1/10,000,000 1 x 10–71E–7

Planning the Test Introduction to the Serial BERT
8Agilent N4906B Serial BERT, User’s Guide, October 2005
Which Features are Available?
The Serial BERT is available in different options. They differ in the
range of provided bit rates and in the available features.
The N4906B Serial BERT has the following options for defining the bit
range:
• Option 003
Bit rate range: 150 Mbit/s to 3.6 Gbit/s
• Option 012
Bit rate range: 9.5 Gbit/s to 12.5 Gbit/s
Additional options define which features are available:
• Option 101
True differential input
Fast Eye Mask measurement
• Option 102
Clock Data Recovery (CDR)
Extended frequency range 150 Mbit/s to12.5 Gbit/s
• Option 301
True differential input
Please note that the options may be combined.
NOTE Not all functions of the N490x series are available on the N4906B
Serial BERT. In particular, the following functions are not available:
• Advanced measurements (with the exception of the Fast Eye Mask)
•DelayControlInput
Subsequently upgrading your Serial BERT with additional options is
not possible.
To check the options of your Serial BERT, press About in the Help
menu. The About dialog shows the installed option numbers.

Which Test is Appropriate? Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 9
Which Test is Appropriate?
These topics help you to decide on the appropriate test setup for your
device.
Determining How to Test Your Device
The Agilent N4906B Serial BERT can help you test the performance of
components and systems for high-speed digital transmission
equipment.
An important parameter of a digital system is the rate at which errors
occur in the system. The analyzer will compare the bits sent to your
device with the bits received from your device. It will record the
number of bit errors and display results such as the bit error ratio
(BER). In addition, accumulated results can be analyzed to help you
determine what caused the bit errors.
The analyzer can be set up to work with your device in many different
ways. To determine the best measurement setup, you must first decide
how you want to test your device. Before actually setting up and
making measurements, you may want to consider the following
questions:
• What is the purpose of your test?
• What are the testing requirements of your device?
What is the Purpose of Your Test?
Does the purpose of your test fall under one of the following
categories?
• To monitor instantaneous BER during measurement setup,
experiments, and adjustments. See “Instantaneous Measurements”
on page 148.
• To measure and log error performance over time. See “Accumulated
Measurements” on page 153.
• To measure the eye height and width of the incoming data signal at
specific alignment BER thresholds. See “Eye Measurements” on
page 162.

Planning the Test Which Test is Appropriate?
10 Agilent N4906B Serial BERT, User’s Guide, October 2005
The following references may also be helpful in determining how to
test your device.
• For a list of recommended patterns for your device and application,
see “When to Use Which Pattern?” on page 22.
• For a list of recommended connection diagrams for your device and
application, see “Connecting the DUT” on page 13.
What are the Testing Requirements of Your Device?
Considering the requirements of your device will help you choose
which instrument functions to use during the test setup and when
making measurements.
• Do you need to use a custom test pattern?
If you have a long series of 1's or 0's in your custom pattern, be sure
to avoid false sync. See “What is False Synchronization?” on
page 114
• Do you want to use alternating patterns?
Then you must first import or create a custom pattern that contains
an A half (pattern A) and B half (pattern B). See “Pattern
Alternation” on page 76.
• Are you aware of how custom pattern size can affect the pattern
output?
See “Why the Serial BERT Repeats Memory-Based Patterns” on
page 28.
• Does your device change the input pattern it receives?
If your device inverts logic, then select Data Inverted in the
Sampling Point Setup window. If your device changes patterns in
other ways, then you must know the expected output pattern and
select it as the error detector reference pattern.
• What logic family is your device compatible with?
The pattern generator has preset voltage levels to work with ECL,
SCFL, LVPECL, LVDS, and CML. Be sure to select the correct logic
family. See “Understanding how the Serial BERT Uses Logic
Families and Terminations” on page 56.
• What is the input termination voltage of your device?
Make sure it is the same voltage as displayed in the pattern
generator termination list.

Which Test is Appropriate? Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 11
• What termination voltage is the output of your device designed to
work with?
Make sure it is set for the error detector’s data port termination.
See “Data In Port Termination” on page 87.
• What bit rate do you need to test your device at?
The Serial BERT allows you to run tests from 150 Mb/s up to
12.5 Gb/s (depending on the options with which you bought the
instrument). See “Error Detector Bit Rate” on page 96 for more
information.
• Does your device require differential inputs?
As complementary outputs, Data/Clock Out and Data/Clock Out
may satisfy this requirement. See “Diagram 2. Connections for
Differential Inputs” on page 14.
• Is the output of your device noisy or very small in amplitude?
You may need to manually set up a sampling point. See “When
Should You Adjust the Sampling Point Manually?” on page 101.
• Do you want to check the BER in bursts (for example, for loop
testing applications)?
The Serial BERT provides capabilities that help you set up and run
burst tests. See “Introduction to Burst Sync Mode” on page 117.
• Are you aware of how the sync mode setting can affect the way
errors are measured and displayed?
See “What Type of Synchronization Should You Use?” on page 113.
Test Times and Confidence Levels
A true BER measurement must be statistically valid. Because it is not
possible to predict with certainty when errors will occur, your device
must be tested long enough to have confidence in its BER
performance. The table below lists the test times required for different
BERs at specific bit rates.
NOTE The test times in this table are valid for continuous measurements. If
measurements are made in bursts, the test times will be longer
(continuous test time divided by the burst duty cycle times the burst
sync ratio). See “Introduction to Burst Sync Mode” on page 117 for
background information.

Planning the Test Which Test is Appropriate?
12 Agilent N4906B Serial BERT, User’s Guide, October 2005
The test times for 95% confidence level are:
The formula for confidence level is as follows:
C = 1 - e^-nb
Where:
C = degree of confidence (0.95 = 95%)
e = natural base number
n = number of bits examined without error
b = desired residual BER
You may want to prove that your device has a certain residual BER. If
you know this desired BER and the desired confidence level, you can
calculate the number of bits that must be measured without error. The
number of bits, in turn, can be translated into a period of time at a
certain bit rate. That is what is done in the above table.
The following example shows how to calculate the number of bits if the
desired BER (b) is 1E-10 and the desired confidence level (C) is 95%:
1Change formula “C = 1 – e^-nb” to solve for the number of bits (n)
n = -ln(1-C)/b
2Replace variables C and b
n = - ln(1 - 0.95)/1E-10
3Calculate the number of bits
n = - ln(1 - 0.95)/1E-10 = 2.99/1E-10 = 2.99E+10 bits
4Calculate the time period at the STM-16/OC-48 bit rate (2.48832
Gb/s)
2.99E+10 / 2.48832E+9 = 12.016 seconds
BER
STM-64/OC-192
(9.95328 Gb/s)
STM-16c/OC-48c
(2.48832 Gb/s)
STM-4c/OC-12c
(622.08 Mb/s)
STM-1/OC-3
(155.52 Mb/s)
1E-14 ~ 8.4 hours ~ 1.4 days ~ 5.6 days ~ 22.4 days
1E-13 ~ 50 minutes ~ 3.3 hours ~ 13 hours ~ 2.2 days
1E-12 ~ 5 minutes ~ 20 minutes ~ 80 minutes ~ 5.3 hours
1E-11 ~ 30 seconds ~ 2 minutes ~ 8 minutes ~ 32 minutes
1E-10 ~ 3 seconds ~ 12 seconds ~ 48 seconds ~ 3.2 minutes

Connecting the DUT Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 13
Connecting the DUT
This section provides information on how to connect your DUT for
several common test scenarios.
NOTE The pattern generator’s Data Out and Clock Out ports must be
terminated with 50 Ωif they are not connected.
The following procedure is recommended when setting up a test:
1If your DUT can handle 0 V, press the 0V (Disable) button in the PG
Output Setup screen.
The pattern generator’s Data Out and Clock Out outputs are set to
0 V. This is indicated in the PG Output Setup screen.
2Connect the DUT as necessary.
3Terminate any non-connected Data Out and Clock Out ports
(normal and complementary).
4If the outputs are disabled, press the 0V (Disable) button to enable
them.
To avoid damaging your device, set up the devices properly before
making connections.
CAUTION ESD can damage or destroy electronic components. Coaxial cables
with both ends unconnected may store electrostatic charges. Before
connecting any coaxial cable of this sort to a device or instrument,
momentarily short the center and outer conductors of the cable. When
making connections, ensure the proper use of a grounded, resistor-
isolated wrist strap.

Planning the Test Connecting the DUT
14 Agilent N4906B Serial BERT, User’s Guide, October 2005
Connect your device according to the diagrams below:
Diagram 1. Connections for Different In/Out Data Rates
Often used for multiplexers, or when the data rate received by the
device is not equal to the data rate sent from the device.
Diagram 2. Connections for Differential Inputs
NOTE Depending on the options of your Serial BERT, the following functions
may not be valid for your instrument. See “Which Features are
Available?” on page 8 for a description of the available options.
Application is the same as in Diagram 1. Illustrates how to connect to
a device requiring differential signals.

Connecting the DUT Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 15
Diagram 3. Connections for an Amplifier
Often used for amplifiers.
Diagram 4. Connections for a Flip-Flop
Often used for flip-flops.
Diagram 5. Connections for a MUX/DEMUX Pair
Used to test multiplexer/demultiplexer (MUX/DEMUX) pairs. For
accurate measurement results, the timing of data signals between the
MUX/DEMUX pair must be set properly.

Planning the Test Connecting the DUT
16 Agilent N4906B Serial BERT, User’s Guide, October 2005
Diagram 6. Connections for a DCA or Oscilloscope
(PG only)
Used for measuring the output waveform of your device. For the least
amount of jitter, the clock output signal may be used as a trigger for
the oscilloscope.
Diagram 7. Connections for a SONET/SDH Receiver
(PG only)
Often used with network equipment, such as SONET/SDH receivers.
The device shown may or may not require a clock signal.

Connecting the DUT Planning the Test
Agilent N4906B Serial BERT, User’s Guide, October 2005 17
Diagram 8. Connections for an External Data Source
(ED only)
Used when the device is stimulated by another data source. Illustrates
the use of an oscilloscope in addition to the error detector.
NOTE As in all setups, the pattern sent to the error detector must be the
same as the internal reference pattern of the error detector. Dynamic
patterns and/or patterns with live payloads cannot be used.
NOTE Diagrams 1 through 8 can use an external clock reference connected to
the Clock In port of the pattern generator, if desired.

Planning the Test Connecting the DUT
18 Agilent N4906B Serial BERT, User’s Guide, October 2005

Agilent N4906B Serial BERT, User’s Guide, October 2005 19
Setting up Patterns
The purpose of data patterns is to simulate the type of data that your
device might receive in the real world. Different patterns present
different data loads to your device, which can cause variations in the
bit error ratio. A bit pattern is sent from the pattern generator to your
device. At the same time, the expected output pattern of your device is
internally generated in the error detector (to provide a reference).
Selecting a pattern is the first step in setting up a BER measurement.
The Serial BERT provides various patterns to fulfill most standard
testing needs.
How does the Serial BERT Generate Patterns?
The Serial BERT has two possibilities for generating patterns: either
by directly generating them from the hardware, or by loading patterns
into the memory and generating the output according to the pattern in
the memory. These memory-based patterns can be either user
patterns (file-based), or software-generated patterns.
Hardware-Generated Patterns The hardware-generated patterns available with the Serial BERT are
PRBS 2^n –1 patterns. They provide long, high-speed, random traffic
patterns that can be used for testing a wide range of devices. These
patterns cannot be manipulated in any way.
Memory-Based Patterns The memory-based approach is more flexible. It makes it possible to
define any pattern (within the physical limits of the memory) for
defining the output. The Serial BERT provides two possibilities for
defining the output: by defining user patterns or by selecting a
software-generated pattern.
User Patterns User patterns are file-based, editable patterns. These may be patterns
that you set up using the Serial BERT’s Pattern Editor, or any of the
patterns delivered with the Serial BERT. You can easily define your
own patterns for any special requirements.

Setting up Patterns
20 Agilent N4906B Serial BERT, User’s Guide, October 2005
Software-Generated Patterns The Serial BERT can also generate various PRBS 2^n patterns with a
range of polynomes from 7 to 23. These patterns can be further
modified by setting special mark densities (ratio of 1’s to total bits) or
by defining the zero substitution.
What Patterns are Available?
The Serial BERT offers various industry standard and customized
patterns for many BER testing scenarios.
The following graphic illustrates what patterns are available on the
Serial BERT. Note that there are two main branches, corresponding to
the hardware-generated and memory-based patterns, and the
memory-based patterns are further broken down into software-
generated patterns and user patterns.
See “Example Patterns” on page 29 for a complete listing of the
example patterns.
Pattern Family Tree
User Patterns
Hardware-Generated
Patterns
Custom User
Patterns
Example Patterns
in C:\N490
X \Pattern\Demo
2^n-1 PRBS
FDDI Fiber-Channel
Gigabit Ethernet 2^n PRBS 2^n PRBS Mark Density SDH SONET
Industry Standard Pattern or
modified Industry Standard Pattern
PRBS
Software-Generated Patterns
Zero Substitution Mark Density
Memory-Based Patterns