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DMI Compliance & Sink Characterization Using DTG5000 Series Data Timing Generator
Application Note
11
www.tektronix.com/signal_sources
Software Tools For Sink Tests
Sink tests, like Source tests, can take a lot of time. In
case of Sink tests, there is the complexity of controlling
several tools to conclude a measurement, as well as
the challenge of precisely setting jitter parameters.
All this makes automation an implicit requirement.
The TDSHT3 application package described earlier
is optimized to speed HDMI testing and compliance
work. TDSHT3 makes uses the GPIB interface to
remotely control various parameters. The oscilloscope
connects to the DTG5000 Series using a GPIB cable
and to the AWG or arbitrary function generator using
a GPIB-USB-B cable or E-Net to GPIB converter
(available from National Instruments).
Many HDMI test setups and measurements reside
within the TDSHT3 application; others can be down-
loaded at www.tek.com. Table 4 lists the standard
setups, and the CTS tests to which they apply.
Testing HDMI Cables
HDMI cables can be characterized in either or both of
two ways: time-domain reflectometry (TDR) and eye
diagram testing. The TDR technique uses a digital
sampling oscilloscope to measur
e the impedance
characteristics of a cable with gr
eat pr
ecision, but
cannot verify waveform quality.
Eye diagram testing involves displaying a waveform
that consists of rising and falling edges superimposed
in such a way that there is an “eye” opening bounded
on all sides by positive-going and negative-going
transitions. T
ypically there is a region within this
opening that must not be violated by any waveform
data point. To do so would indicate insufficient
signal amplitude, slow rise or fall times, jitter
, or a
combination of these aberrations.
The DTG5000 Series can produce standard HDMI
signals for use as test data in eye diagram mask
testing to reveal the true waveform performance of
the cable. First, transmitter performance can be
verified by inserting the test data signals ahead of the
transmitter and per
for
ming the eye mask test at the
transmitter output. Once this is confirmed, the test
data signals can be inser
ted at the beginning of the
cable and eye mask testing performed with the
TDSHT3 package at the end. If jitter violates the
eye mask, the cable has insufficient bandwidth. If
the signals have insufficient level, the cable loss is
too high. Figure 10 is an eye diagram captured by
the TDSHT3 application software package.
Conclusion
Compliance testing of HDMI Sink devices is no longer
limited to the use of custom data sour
ces and tedious
manual methods. The DTG5000 Series high perform-
ance data generators solve the problem by providing
a full complement of highly accurate data signals with
precise control over the signal parameters. Testing to
DVI/HDMI standards receiver products over a wide
range of operating conditions can now be automated
using simple, graphical controls and a set of industry-
standar
d adapter accessories.
References
1. HDMI Specifications Version 1.0
2. Compliance Test Specifications (CTS) Version 1.0a
3. Physical Layer Compliance Testing for HDMI
Using TDSHT3 HDMI Compliance T
est Softwar
e
(Tektronix Application Note 61W-17974-1)
F
igure 10.
HDMI eye diagram captured with TDSHT3 application software.