USB 80Gbps: What's New in USB4 Version 2?
In October 2022, the Universal Standard Bus Implementers Forum (USB-IF) announced USB4® Version 2.0, the next generation of the USB standard. Coming three years after the release of USB4, this new standard has created quite a buzz in the industry for three reasons:
- The announcement comes on the heels of the recent EU law mandating USB Type-C® as the “common charger” for smartphones and other mobile devices starting in 2024. The market for USB devices is about to grow as tech companies who previously resisted the USB ecosystem will have to conform to be compliant.
- The standard update is part of a larger trend in the high-speed digital communications space of doubling data rates in the pursuit of increasingly faster data speeds. In data centers, wireless communications, and consumer devices, speeds are rapidly increasing to satisfy the high data processing demand created by technologies such as artificial intelligence, augmented and virtual reality, and heavy video streaming.
- USB4 Version 2.0 is the first USB standard to embrace pulse amplitude modulation (PAM) signaling. The Ethernet standards, OIF CEI and IEEE 802.3, and PCI Express, have moved to PAM4 in recent generations to increase data speeds. The USB-IF has chosen PAM3 for the next generation of USB.
What’s New in Version 2?
USB4 Version 2.0, also known as USB 80Gbps, supports 80 Gb/s data transmissions (40 Gb/s per lane with two lanes in each direction). It is the first USB standard to use higher modulation signaling, opting for 25.6 Gbaud per second PAM3 signaling. Like previous generations, it will be backward compatible for previous versions of USB and Thunderbolt 3. Likewise, the standard will contain updates to align with the latest versions of the DisplayPort (DP) and Peripheral Component Interconnect Express (PCIe) standards. USB4 Version 2.0 supports PCIe and DP protocols via tunneling over the USB4 fabric. \
Figure 2: PAM3 signaling increases the number of bits (about 1.58 bits) transmitted per cycle
An interesting detail from the announcement: USB Type-C will now allow for asymmetrical transmissions for certain applications. In practice, this means using three 40 Gb/s USB lanes to transmit 120 Gb/s in one direction while using one lane to transmit 40 Gb/s in the other direction, as opposed to the default two lanes in each direction topology.
The USB-PD 3.1 specification has also been updated to enable up to 240W of power delivery over USB Type-C cables, increasing the number of USB-powered applications. The USB Type-C specification has likewise been updated to support the new standards. All these developments are building toward the USB-IF’s goal of becoming the primary I/O connector for consumer electronics, providing data, power, audio, and display connections between all devices.
In addition to releasing the first version of the specifications, the USB-IF revealed new guidelines for branding and marketing. The guidelines are aimed at helping consumers decipher the compatibility of their USB devices and cables. Prior generations have confused customers with names like USB 3.2 Gen 2x2, also known as “SuperSpeed USB 20Gbps”. The branding guidelines will make it easier for consumers to identify the speed and power capabilities of their ports and cables. USB4 Version 2.0 will be known to consumers simply as “USB 80Gbps,” simplifying the branding to clarify data speeds.
Figure 4: The USB-IF has made branding updates a priority after recognizing gaps in consumer knowledge around USB standards.
USB4 Version 2.0 Testing Solutions
It is still early days for USB4 Version 2.0, but as digital developers begin designing and developing with the new standard, we will learn more about its effects on developers and the consumer electronics industry. As shown in Figure 5, The USB-IF predicts that the USB4 Version 2.0 compliance test specification will not be fully completed until later in 2023. The first certified USB 80Gbps devices likely won’t be hitting the market until late 2023 or early 2024. After that, the compliance test changes will be rolled into the primary USB4 certification.
Figure 5: USB-IF certification timeline for USB4 Version 2.0.
As a member of the USB-IF, Keysight Technologies has enabled USB4 Version 2.0 pathfinding with the USB-IF, joining the research and development efforts to deliver design and validation solutions to early adopters of the new standard. Read the press release for a full list of Keysight’s USB4 Version 2.0 design and validation solutions.
USB4®, USB Type-C® and USB-C® are registered trademarks of USB Implementers Forum.
All images courtesy USB Implementers Forum. Images sources from USB-IF Developer Days, November 2022.