How to Meet New USB4 Gen 3 Type-C Reliability and Signal Integrity Requirements
Contributed By Digi-Key's North American Editors
The USB4 interface with its maximum data transfer rate of 40 gigabits per second (Gbits/s) over two lanes has placed additional stress on designers to meet signal integrity and electromagnetic interference (EMI) requirements. Additionally, the now-ubiquitous use of Type-C connectors by multiple data and display protocols requires that they share the available bandwidth over their mutual buses. Designers also need to be sure that the connectors, like all USB4 components, are certified by multiple standards organizations. Other design challenges include mitigating the risk of mechanical damage due to incorrect plug insertion, and the need to adapt to end products and usage models that require greater robustness and more advanced features.
The USB Type-C® specification establishes connector requirements that address the evolving needs of systems and devices while maintaining compatibility with all of the functional benefits of existing USB forms. This article explains the configuration and features of the USB Type-C connector and discusses the applications for which it is used. It then introduces USB4-certified USB Type-C connector receptacle examples from Amphenol ICC that support all the advanced features outlined in the specification, including additional features that both reduce EMI and improve the reliability and mechanical integrity of the connector.
USB4 Gen 3 Type-C connector
The USB Type-C plugs and receptacles are specified by the USB Implementers Forum (USB-IF) in the document, “USB Type-C Cable and Connector Specification Revision 2.0”, which covers USB4 over USB- Type-C connectors and is available at no cost on the USB-IF website.
The USB-C connector uses 24 pins and provides USB Power Delivery (USB PD), data transfer, audio, and video output in one connector. The most noticeable thing about USB-C connectors is that they are reversible; that is, the plug may be inserted into the receptacle in either orientation—a feature greatly appreciated by users who have had problems with insertion of the old USB-A connectors. This capability can be seen when looking at the signal assignments for the USB-C plugs and receptacles (Figure 1).
The center pin layout shown in Figure 1 is that of the receptacle. There are two plug orientations shown: the upper one is for normal orientation and the lower one shows the plug rotated 180˚. Regardless of the plug direction, corresponding signals are matched upon plug insertion.
Figure 1: The signal assignments for the USB-C plug connector (top and bottom) and receptacle (middle) viewed looking into each part, shows that 180˚ plug rotation still results in the correct matching of corresponding signals upon insertion. (Image source: Art Pini)
The signal groups within USB-C connectors—shown highlighted in Table 1, with matching colors of the corresponding connector pin signals from Figure 1—show the versatility of USB-C connectors for use in diverse applications. The high-speed differential signal lanes can support transfer rates of up to 40 Gbits/s and are used for both USB4 and alternate-mode and tunneling protocols.
Table 1: A summary of USB4 connector signals that includes two high-speed differential signal lanes, a USB 2 differential signal path, and power and interface control signals. Signal group fill colors match those of the corresponding connector pin signals shown in Figure 1. (Table source: Art Pini)
The alternate-mode protocols supported with USB4 include Thunderbolt, DisplayPort (DP), Mobile High-Definition Link (MHL), Peripheral Component Interconnect Express (PCIe), and High-Definition Multimedia Interface (HDMI). Additional alternate-mode protocols can be defined and enabled via a USB PD protocol handshake using structured, vendor-defined messages (VDM) to discover and configure the alternate modes.
USB PD also allows devices to negotiate the power level supplied by the source. USB4 supports a maximum power level of 100 watts at 20 volts at 5 amperes (A). This capability may require a programmable power supply. Power control and active cables allow fast charging. The power contracts between devices are negotiated using the configuration channel (CC) line using biphase mark coding at 300 kilobaud, half-duplex.
There are many advantages to using a common connector for all of these different protocols covering applications in audio, video, data storage, and data communications. It also allows for the definition of new and emerging protocols as they are being developed.
The connector pin assignments show a common sense layout to maximize signal integrity. For example, the high-speed and USB 2 data lines are differential to minimize crosstalk and EMI. In addition, all data lines are run between power and ground buses or other low-bandwidth signal lines to provide isolation, and the high-speed data lines are placed on opposite sides of the layout to minimize lane-to-lane crosstalk.
Features of Amphenol ICC USB4 receptacle product offerings
To help meet the design challenges of USB4, Amphenol ICC has introduced four USB4 Gen 3 receptacles that outperform the existing standard. They are next-generation connectors that meet the standard’s high data transmission rates of up to 40 Gbits/s, and are compatible with USB PD, with the Thunderbolt interface combining power charging, tunneling USB, and PCIe data transfer through a single Type-C connector. These connectors also support both DisplayPort video and audio with 4K ultra high definition (UHD) at a 60 Hertz (Hz) refresh rate.
A significant USB4 feature of these connectors is their ability to dynamically optimize the bandwidth while transferring video and data. Per the standard, the new USB4 connectors are backward compatible, supporting previous USB versions including USB 2, 3.1, and 3.2, but with rotatable plug and cable orientation for the much-enhanced USB user experience. The connectors’ small size and functional versatility make them ideal for incorporation into emerging technologies.
Mechanical design supports power and durability
The Amphenol ICC USB4 receptacles are designed to provide excellent performance for 10,000 mating cycles, providing high durability and reduced wear-out from cyclic operations. A focus on high-quality copper metal alloys in the design of the conductive paths ensures low-loss 40 milliohm (mΩ) contact resistance, and an extended 5 A current rating for USB power delivery of up to 100 watts.
The connectors use an improved sidewall for the middle plate that maximizes the contact area and stabilizes contact performance making it wiggle free (Figure 2).
Figure 2: The enhanced sidewall design of the Amphenol ICC USB4 receptacles provides “wiggle-free” connections with better EMI protection and improved mechanical protection against incorrect plug insertion. (Image source: Amphenol ICC)
The enhanced mechanical features include an extended sidewall plate that reaches to the corner of the receptacle tongue to prevent non-Type-C plugs, like the micro-USB plug, from being inserted. The same sidewall is grounded with the mid-plate, providing additional shielding and reduced EMI. Added dimples on the inner shield guide the plug and maintain the correct plug body position during insertion. The entire mechanical assembly provides stable locking performance and maximum contact area overlap of the mating conductive surfaces, minimizing contact resistance. A strong audible click ensures full insertion.
The Amphenol ICC product family
There are four USB4 Type-C receptacles in the Amphenol ICC product offering (Figure 3).
Figure 3: The Amphenol ICC USB4 Gen 3 Type C receptacles include three top-mount versions and one mid-mount version. (Image source: Amphenol ICC)
The GSB4D313302Y1HR top-mount receptacle with right angle through-hole mounting is currently certified by the USB-IF and recommended by Intel for Thunderbolt 4 use. Its outer shell has a uniform cross section front to back with a 1.58 millimeter (mm) center height (distance from mounting plane to connector tongue).
The 12402056E512A and 12402073E512A are also top-mount receptacles with through-hole mounting, but they have a rectangular outer shell with a center height of 1.57 mm. Standards certification of these receptacles is pending (at the time of this writing).
The 12402075E512A is a mid-mount receptacle with a center height of only 0.47 mm for a more compact configuration. It also uses through-hole mounting. Certification of this receptacle is also pending at this time.
All of these receptacles are rated for operation over a temperature range of -40°C to +85°C, making them a good match for in-vehicle applications.
USB4 connector applications
These receptacles will find use in storage, automotive infotainment, home entertainment, docking, peripheral interfaces (monitor/display, projector), and other consumer applications like notebooks (laptops) and tablets. Their small size, support for multiple modes, and power control provide tremendous versatility.
The USB Type-C connector, with its ability to handle multiple high-speed protocols and power levels, will find more applications as users look for faster data transfer rates, fast charge capability, and connector simplicity. With USB4, users get alternate modes and tunneling support. These enhancements will ensure wider adoption of USB4 across more varied and potentially harsher environments and applications. To help designers account for this, the Amphenol ICC USB4 receptacles are designed to exceed the basic USB-IF specification, mitigating the effects of EMI, and ensuring good connections over many cycles and wide temperature ranges.
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