Power Up Your Knowledge: How to Test USB-C Cable Like a Pro

USB Type-C, or USB-C in shorter form, is a breakthrough connector standard designed to meet technology demands. USB-C supports computers and electronic devices at a faster transfer rate, with higher power delivery and flexible connectivity. It offers alternate modes to support DisplayPort and HDMI.
While every USB-C port looks the same, not every port offers the same capabilities and functions. Here are answers to common questions to help you understand more about USB-C testing.

Is Thunderbolt the Same as USB-C?

Thunderbolt and USB-C are not the same, though they share some characteristics. USB-C is a connector type or form factor that connects computers and other electronic devices. Thunderbolt uses the same physical connector as USB-C. But Thunderbolt offers faster data transfer speeds and supports additional features, such as daisy-chaining multiple devices and providing power to connected devices.

Thunderbolt and USB4 are communication standards or protocols that provide a set of features for a computer to interact with devices through a USB-C connection. In this case, USB-C is a connector that supports USB and Thunderbolt technologies. The port is universal, but the compatibility specification depends on each protocol's data transfer rate, charging speed, and additional capabilities.

How Do You Test a USB-C Cable?

Cable manufacturers, product designers, and system integrators perform the standard USB-C cable compliance tests based on the compliance test specification (CTS) defined by the USB Implementers Forum (USB-IF). CTS ensures that cable manufacturers and product designers produce standards-compliant USB-C cables and devices that meet interoperability requirements. Only products that complete USB-IF certification may use the certified USB marks to identify the performance and protocols supported.
The Keysight USB-C cable and connector compliance test solution is based on the latest USB-C CTS release. The specification defines the test requirements for each type of cable assembly: full-featured Type-C / Type-C-to-legacy cables and supported USB technologies. Besides passive cables, USB-C also supports USB Type-C full-feature active cables. See how you can test a USB-C cable, as well as Thunderbolt 4 and Thunderbolt 3 cables, using Keysight S94USBCB compliance software.

Figure 1. The Keysight USB Type-C high-speed interconnects test solution supports 20-port fully automated mode (with a switch matrix) and four-port mode (without a switch matrix)

What Are the Test Challenges for USB-C?

The increased bit rates of 40 Gbps to support the USB4 protocol (and 80 Gbps to support USB4 version 2.0) bring additional signal integrity challenges and introduce more stringent test requirements than previous generations. Testing the new USB4 Type-C standard cable assemblies requires a series of integrated test parameters corresponding to the incidental and reflective behaviors over a frequency range. The newly introduced channel operating margin (COM) and integrated S-parameters tests require up to 44 sets of S-parameter measurements and execution of USB-IF compliance test tools to verify the results.
The conventional way of testing USB-C cables using a four-port vector network analyzer (VNA) is manual. Calibration, measurement setup, and test execution are time-consuming and prone to user errors. One way to automate and speed up USB compliance testing is by using modular multiport network analyzers such as PXIe VNAs or a switch matrix system capable of handling multiport measurements with USB-C compliance test software.
Keysight Technologies has enabled USB-C high-speed interconnect test solutions to automate the time-consuming and error-prone process of setting up manual port reconnections and USB-IF standards compliance tools. The solution includes the USB Type-C interconnects compliance test software, a four-port VNA, and a 20-port switch matrix system to lower the cost of multiport testing.\

What Is Channel Operating Margin or COM?

The USB-IF introduces a COM test requirement for USB4 Gen 3 and USB4 Gen 4 Type-C passive cable assemblies and receptacle connectors. COM is the channel's signal-to-noise ratio to measure channel electrical quality. To calculate COM, the measured cable assembly S-parameters cascade with the reference host and device models to form the complete channel. The USB-IF has created a compliance testing tool to calculate COM. It requires 28 sets of S-parameters from transmitter and receiver pairs when using a four-port VNA. Download the 30-day free trial license and learn how Keysight's high-speed interconnects compliance automation software helps simplify the extended setup time.

What Is Fixture De-embedding in USB-C Cable Testing?

Test engineers conduct electrical characterization of a USB-C high-speed signal using a VNA with a test fixture to connect the cable device under test to VNA ports. Complete removal of the test fixture is crucial to prevent fixture artifacts from affecting test results, especially at higher frequencies. But how? The answer is simple — through calibration or a de-embedding process.
Keysight recommends the automatic fixture removal (AFR) de-embedding technique for USB4 Type-C cable testing. AFR can dramatically reduce the complexity of directly measuring the S-parameters of the fixture. Each S-parameter element of the fixture is uniquely extracted and transforms the complex error-correction algorithm into an output AFR file that can load into VNA firmware for de-embedding operation. The 2X thru AFR is part of the S94USBCB compliance test software.
Figure 2 illustrates a significant loss at higher frequencies without proper calibration and de-embedding processes during the measurement. AFR is a rigorous approach to removing fixture effects to measure the device's actual performance. Learn more about de-embedding in the ABCs of De-embedding application note.

Figure 2. Calibration and AFR effects on USB cable measurement

The Next Generation: USB4 Version 2.0

USB4 is a hardware interface that supports several protocols through the USB Type-C connector. Based on the Thunderbolt protocol specification, the USB4 architecture doubles the bandwidth of USB and enables multiple simultaneous data and display protocols. In October 2022, the USB-IF announced USB4 version 2.0 (also known as USB4 Gen 4), the next generation of the USB standard. With USB4 Gen 4, each link will have two lanes running at 40 Gbps, achieving an aggregate of 80 Gbps with a USB-C port.

Figure 3. Data speeds supported by USB4 and Thunderbolt 4. Note that USB-C is backward compatible with USB 2.0 and USB 3.2.

As an active member of the USB-IF and a key contributor to all the latest USB working groups, Keysight delivers comprehensive and fast-to-market design and validation solutions for the new standard. Read the press release for recent Keysight USB4 version 2.0 design and validation solutions.