Simplifying 1394 Cable Assembly Testing Using
Fourier Transform
For high-speed serial bus applications such
as IEEE-1394, the integrity of the data transfer relies
on the quality of the 1394 cable assemblies. The current
test requirements for 1394 cable assemblies are listed in
the 1394 Trade Association class document “1394 Connector
and Cable Compliant Test Criteria.” The specified requirements
are in compliance with both IEEE1394-1995 and IEEE1394a-2000.
Testing of the electrical parameters, which determines the
signal quality, is specified in Performance Group I: High
Speed Electrical Functionality. The complete carry out of
the specified Group I testing is expensive, complex and
time-consuming. It is impractical to make the specified
testing on a production line of cable assemblies.
The Group I test criteria include the testing
of Characteristic Impedance in the time domain using a Time
Domain Reflectometer (TDR), and Attenuation, Velocity of
Propagation Delay, Skew, and Crosstalk in the frequency
domain using a network analyzer. DC resistance is also specified
and it is usually measured with a LCR meter. These criteria
can be simplified to allow a lower initial investment and
a lower cost of testing, and still ensure proper performance
requirements. This is possible with the conversion of time
domain requirements to frequency domain by Fourier transforms,
and then testing in the frequency domain against these limits.
The new requirements of the new testing procedure
would be:
- Test Impedance in the Frequency Domain.
- Test AC Resistance
- Remove the Testing of Velocity of Propagation Delay
and Skew
- No change for Crosstalk and Attenuation.
The new simplified test setup would be much simpler, and be
space saving, with only a few key components. The key components
would be:
- Network Analyzer – the device used to perform fundamental
frequency domain measurements.
- Test fixture and Automatic switch – test fixture is
used to provide a constant interface between the measuring
instrument and the cable assembly under testing. The automatic
s3itch provides a controlled, reliable signal path that
automates and simplifies the testing process to produce
repeatable results.
- Control and Reporting Software – the software is used
to automatically control the network analyzer, process
the test data and to provide test reports. The software
permits non=technical personnel to run tests, enable automatic
comparison of test results to the IEEE-1394 standard,
eliminates operator error, improves test time, and results
in more consistent, reliable results.
The current IEEE-1394 standard should apply to type and
certification testing of bulk cables and cable assemblies,
but a less complex and less costly testing protocol is recommended
for cable assembly production, allowing for cable assembly
manufacturers to adhere more consistently and to ensure
success with the IEEE-1394 standard.
