April 1, 2016
We all have several variations of USB cables we use in our daily lives to connect and power devices: Type-A, -B, Micro, Mini and more. Anyone who uses computers and peripherals knows USB standard A/B connectors must be plugged in in a single direction. Compared with these existing types of USB cables, Type-C cables offer the usability advantage of being both symmetrical and reversible. USB Type-C is a breakthrough standard designed to meet the demand for ever smaller and thinner computers and devices, higher-speed data and more power and flexibility. It provides:
• dynamic power and transmission of USB 2.0 with other protocols;
• the ability to be an interface for new and future devices;
• backward compatibility; and
• ease-of-use as a result of reversibility.
Designing for USB Type-C
Consumers using USB Type-C enabled products will find them to be much more capable and simple to use. Engineers, however, have a lot more complexity to manage during design and test, especially when considering the many different scenarios of functionality Type-C offers.
Design and test engineers face a number of challenges as they work to upgrade and integrate USB Type-C into products, while ensuring interoperability and achieving test compliance.
Previous versions with 4- or 8-pin power, ground and data connection will move to 24 pins with multiple power, ground, Tx/Rx lines, control lines and more. Also, compliance test standards have increased and are more complex due to higher data transmission speeds, more power and additional functionality.
The USB Type-C cable and connector not only provides backward USB compatibility, but also increased functionality for power management and data transmission. USB Type-C power delivery provides up to 20 volts, 5 amps and 100 watts for dynamic power and charging of different devices. The transmit/receive (Tx/Rx) pairs can be used for USB or “guest protocols” such as DisplayPort, MHL or Thunderbolt data transfer.
Type-C data transfer rates are up to 20Gbps (Thunderbolt) with the ability to achieve 40Gbps in the future. These new capabilities create a greater challenge for engineers working to ensure the interoperability of their USB channel and devices by performing USB-IF standard conformance tests.
Dealing with this new complexity starts with knowing how your Type-C device will function as early as possible in the design process. Physical layer design simulation helps ensure a valid layout with optimal performance, test compliance for new device designs and prevent possible re-designs. To avoid costly hardware prototyping cycles and to identify problems early, it is best to perform simulation of the design for compliance testing.
Simulation and design validation for Type-C device performance involves characterization of clock and data signals for the transmitter, receiver and the channel for various stress signals and helps ensure interoperability.
Once you have a physical prototype, the Type-C specification introduces new test and validation implications. Successful testing requires accurate and standard compliant test instruments, software and fixtures. It begins with USB power delivery. The single CC (configuration channel) line negotiates which alternate modes you’re running, how power will flow and provider/consumer relationships. Then, for whichever technology (USB, DisplayPort, Thunderbolt, etc.) being used, the ability to quickly and accurately measure and validate key aspects of the transmitted eye will be critical for a transmitter test. Flexible signal generation and bit error detection are key for receiver test validation.
For those involved in cable assemblies, it’s critical to quickly address signal integrity issues that can negatively affect system performance as bit rates increase, while accelerating interconnect testing and characterization. You’ll now need to consider high-speed interconnect analysis, including impedance, S-parameters and eye diagrams.
The USB Type-C connector will add simplicity in our day-to-day lives and complexity for the engineers implementing it. Your goal with Type-C will be to get from debug to characterization to compliance to done as quickly as possible.