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What is DisplayPort Certification and Why is Individual Quality Control Just as Important?
Jessica Hopkins

DisplayPort (DP) is a digital interface that transmits audio and video signals. DisplayPort was created to replace DVI and VGA cables in exchange for a higher performing standard that could transfer high quality video and audio signals, as well as offer other features that could allow for better interoperability between advancing technologies.

Video Electronics Standards Association, or VESA, established and continues to oversee the development of the DisplayPort interface, now one of the most widely adopted video display standards in the electronics industry alongside HDMI. VESA has introduced multiple DP specifications over the years, with each new iteration offering higher bandwidth, faster speeds, and new capabilities. For more information on the latest DisplayPort 2.0 spec, check out our blog, “DisplayPort 2.0 is the Latest DisplayPort Spec – How does it Compare to DisplayPort 1.4?”.

To ensure that cable manufacturers are producing up-to-standard DisplayPort cables and other devices, VESA offers a compliance program. The DisplayPort compliance program involves a rigorous set of tests that can typically be performed at an authorized testing center (ATC) or through self-testing methods.

How do Products Obtain DisplayPort Certification?

In order for devices to become DisplayPort certified, manufacturers must submit their product, whether this be a source, sink, media, or cable or adapter, to an authorized testing center and it must pass various tests; these tests include a physical layer test, link layer test, interoperability test, EDID test, Multi-Stream Transport (MST) test, HDCP test, and an HDCP 2.2 test if supported.

Authorized Test Centers will typically test the product using a variety tools, and once a product has determined to past these qualifying tests, manufacturers are permitted to use the compliance logo.

Is Product Certification Enough?

Design certification is necessary to determine conformance to DP specifications, but what about post-certification production line testing to measure quality outputs?

Compliance tests can catch design errors, but it cannot always prevent inconsistencies occurring on the production line, because it is a different ball game altogether. Cables produced on a mass-scale will not always adhere perfectly to the prototyped cable that was tested for compliance. Without a cable testing solution to perform individual quality control on each and every cable coming off the production line, even a certified cable could be defective when it lands in the hands of consumers.

Manufacturers of DisplayPort cables, certified or not, should be verifying cables are up to spec during and after production because variability and human error are factors that influence the finished product. Without any intervention, producing untested cables can lead to bad brand recognition, expensive recalls, and can even be dangerous if cables are used for medical or military purposes.

While many cable manufacturers do perform some type of testing on their products, it is not always sufficient and does not always cover all bases. Statistical Process Control (SPC) is a quality control method that tests random batches of cables to determine the likelihood of the passing rate of all cables. This method is often lower in cost, but is not as accurate as 100% individual quality control, and can allow for unreliable cables to pass inspection.

Video cable manufacturers also often perform functional testing to determine if the cable can simply transmit video and audio, but with the naked-eye, testers cannot easily determine conformance to the cable specification. There are numerous components within the cable that are required to meet certain measurements, including whether pins are properly aligned and whether or not the cable’s signal meets the acceptable bit rate.

Individual Quality Control is Vital to Cable Production Operations

How can cable manufacturers go beyond cable certification and leave behind insufficient testing methods? With Total Phase’s Advanced Cable Tester v2, affordable, complete quality control is attainable.

The Advanced Cable Tester v2 comprehensively tests cables. Interchangeable connector module tests DisplayPort to DisplayPort cables.

This tester supports video cables including HDMI (up to 12.8 Gbps per channel) and DisplayPort (specifications 2.0 and below), as well as other cable types including USB and Apple Lightning. It performs a complete assessment of each cable, testing for conformance to specification. The Advanced Cable Tester v2 tests DisplayPort cables for pin continuity, checking for shorts/opens/routings of all pins, including lane pins and wires that transmit video and audio data, DP hotplug pins and wires, and DP power pins and wires.

An example output of our Pin Continuity test for a passing DisplayPort 1.4 cable is shown below.

Pin Continuity Output of DisplayPort to DisplayPort cable

This tester also measures the DC resistance on all non-high speed wires, as well as tests the cable’s signal quality. Our signal integrity test measures the quality of the signal from one end of the cable to the other, and displays eye diagrams with masks per cable speciation to help visualize these measurements. If any portion of the eye-diagram is touching the mask, the cable will fail this test.

The captures below represent a passing and failing eye-diagram taken from the same DisplayPort 1.4 cable at 8 Gbps per channel. The left channel passes at this bitrate, while the right channel fails. This could affect the quality of signal and lead to corruption of the video or audio data.

Passing signal integrity test for a DisplayPort to DisplayPort 1.4 cable. Failing signal integrity test for a DisplayPort to DisplayPort 1.4 cable.

The Advanced Cable Tester v2 is specially designed for factory settings, offering a rugged design, ethernet connectivity, and local storage. In only a matter of seconds, factory personnel at any level can determine a pass or fail result and for only pennies per test. Read more on the cost-savings benefits of using the Advanced Cable Tester v2 here.

To learn more about how the Advanced Cable Tester v2 can test your DisplayPort cables, please contact us at 1-408-850-6501 or email us at sales@totalphase.com.