Download OFSTP-18

TIA/EIA-526-18
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OFSTP-18
SYSTEMATIC JITTER GENERATION
(From EIA Standards Proposal No. 2269-A, formulated under the cognizance of TIA FO-2.3.
Subcommittee on Digital Systems Jitter and Wander.)
This OFSTP is part of the series of test procedures included within Recommended Standard EIA/TIA-526.
1.
INTRODUCTION
1.1
Intent. The intent of this test procedure is to measure systematic jitter on a digital signal at the
output port of an individual digital equipment, including pattern dependent sources such as intersymbol
interference, finite pulse width, pattern effects, and clock threshold offsets.
1.2
Scope. Since random jitter and systematic jitter are statistically independent, they are
uncorrelated: hence, their powers add. Therefore, to determine the systematic jitter power, subtract the
random jitter power from the total jitter power.
1.3
Safety. All tests performed on optical fiber communication systems of that use a laser or LED in
a test set shall be carried out observing all applicable safety precautions of ANSI Z136.2.
2.
APPLICABLE DOCUMENTS
Test or inspection requirements may include but are not limited to the following references:
EIA TSB19
Telecommunications Systems Bulletin No.
19 “Optical Fiber Digital Transmission
Systems – Consideration for Users and Suppliers”
T1X1,3 Jitter and Wander
Subworking Group
“Jitter Measurement Methodology”
ANSI Z136.2
“American National Standard for the safe use of
Optical fiver communication systems utilizing
Laser diode and LED sources”
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3.
APPARATUS
3.1
The following test equipment is required to perform this test:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Digital Signal Receiver
Digital Signal Generator
Voltmeter
Frequency Synthesizer (Date Rate)
Dividers
Mixer
Variable Delay Line
Low-Pass Filter
Buffer Amplifier
3.2
The following additional test equipment is optional and intended for used when observation of the
output jitter frequency spectrum is required:
1.
Spectrum Analyzer
Note: This section will be expanded in a later issue to call out required attributes and tolerances of test sets.
4.
SAMPLING AND SPECIMENS
The test sample shall be an item of the fiber optic transmission system, as used under normal operating
conditions and having inputs and outputs normally seen by the user of the system. The sample is identified
in Figure 1 as Equipment Under Test (EUT).
5.
PROCEDURE
5.1
Random Jitter Measurement. Determine the random jitter component of the total output jitter
using the following procedure.
5.1.1
Connect the equipment as shown in Figure 1. Verify proper continuity and error-free operation.
5.1.2
Se the Digital Signal Generator to produce a suitable bit sequence (e.g., 11001100…) appropriate
for determining random jitter.
5.1.3
Adjust the Variable Delay until the Voltmeter indicates that the Mixer output is at the center of its
linear region (for a passive Mixer, this corresponds to zero volts dc).
TIA/EIA-526-18
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5.1.4
Measure the Mixer output signal rms voltage.
5.2
Systematic Jitter Measurement. To determine the systematic jitter power, subtract the random
jitter power from the total jitter power. Determining the total power requires the application of a
pseudorandom bit sequence using a technique similar to that described in 5.1 for random jitter.
5.2.1
Connect the equipment as shown in Figure 1. Verify proper continuity and error-free operation.
5.2.2
Set the Digital Signal Generator to provide a pseudo random bit sequence (e.g., 2 23-1)
appropriate for measuring the total output jitter to the equipment under test (EUT).
5.2.3
Adjust the Variable Delay until the Voltmeter indicates that the Mixer output is at the center of its
linear region (for a passive mixer, this corresponds to zero volts DC).
5.2.4
Measure the Mixer total rms output jitter amplitude.
6.
CALCULATIONS OR INTERPERTATION OF RESULTS
6.1
Multiply the Mixer output signal rms voltage measured in 5.1.4 by the conversion factor, 2n/Kp
(where Kp is the Mixer’s phase detection constant in mV/deg and n is the dividing modulus), to obtain the
rms amplitude of the random output jitter.
6.2
Calculate the rms systematic output jitter amplitude using the following relationship:
J = {J
) 2-(J
TOT
)2} ½
RND
rms
rms
(The total rms output jitter is found in 5.2.4 and the ms amplitude of the random output jitter is found in
6.1).
7.
DOCUMENTATION
Test data sheets shall include the following:
Date of test.
Identification of procedure used (OFSTP No.).
Identification of equipment under test (EUT).
7.1.4
Identification of the test equipment used and the measurement uncertainty due to measurement
accuracy and display resolution.
7.1.5
Identification of jumper cable and connector physical parameters.
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7.1.6
Identification of test methods, specific operating conditions, and procedures used.
7.1.7
Results of the test, including ambient or reference point temperature and humidity if available.
7.2
United States military applications require that the following information also be reported for
each test. For other (nonmilitary) applications, this information need not be reported but shall be available
for review upon request:
7.2.1
Names of test personnel.
8.
SPECIFICATION INFORMATION
The following information shall be specified in the Detail Specification:
8.1
A reference to this test procedure if it is to be used.
8.2
Exceptions or deviations that apply to this test procedure.
8.3
Acceptance or failure criteria.
Figure 1. Output Jitter Measurement Configuration – Enhanced Technique
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APPENDIX A
JITTER DEFINITIONS 1
(Nonmandatory Information)
A.1
JITTER
Jitter, or timing variations in the digital signal stream, is produced by terminals and repeated lines. Jitter
specifications for optical fiber digital transmission systems should be consistent with an overall North
American network strategy for the control of jitter. A complete strategy for the control of jitter would
include the recommendation of network jitter limits at hierarchical interfaces, a description of jitter
accumulation models, provision of guidelines for network planning, and presentation of a jitter
measurement methodology.
A.2
DEFINITIONS
A.2.1 Timing Jitter. Timing jitter is defines as the short-term variations of the significant instants of a
digital signal from their ideal positions in time. Here short-term implies phase oscillations of frequency
greater than or equal to 10 Hz. Timing jitter may lead to crosstalk and/or distortion of the original analog
signal and is potential source of slips at the input ports of digital switches. It may also cause slips and
resultant errors in asynchronous digital multiplexes.
A.2.2 Alignment Jitter. Alignment jitter describes the short-term variations between the optimum
sampling instances of a digital signal and the sampling clock derived from it. The only difference between
timing and alignment jitter is the reference used to measure them. Because of this alignment jitter
amplitudes are dependent not only on the jitter on the digital signal, but also on the characteristics of the
clock extraction circuits. Alignment jitter can be used as a measure of the jitter performance of a clock
extraction circuit. As alignment jitter grows, the signal pulse is sampled further from the optimum
sampling instance, increasing the probability of sampling error.
A.2.3 Frequency Deviation. Frequency deviation describes the difference between the instantaneous
frequency of a digital signal and the long-term average frequency of that signal. Errors can occur in
termination equipment that synchronizes incoming signals using a pulse stuffing mechanism (i.e., digital
multiplexes) when the frequency deviation exceeds amplitude and/or duration thresholds.
1
Source: E.I.A. Telecommunications Bulletin No. 19
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APPENDIX B
COMPARISON BETWEEN OFSTP-18 AND IEC, ISO, AND CCITT
REQUIREMENTS
(Nonmandatory Information)
B.1
IEC
It should be noted that, as of this publication date, there are no known IEC test methods that are comparable
to this OFSTP.
B.2
ISO
It should be noted that, as of this publication date, there are no known ISO test methods that are comparable
to this OFSTP.
B.3
CCITT
Similar ANSI T1X1 contribution material can be found in CCITT Recommendations Specifications for
Measuring Equipment, Blue Book, Volume IV-Fascicle IV.4, Supplement No.3.8.