A USB data cable is nothing more than a line plus two heads. This seems simple, but it is not as simple as imagined. A small data line hides a lot of knowledge that you may not know, and the USB type-c comes out. It is even more obvious that you can't underestimate it.
The USB type-c connector that can be plugged in forward and reverse can reduce the trouble of plugging in USB devices. USB type-c also supports the following technologies: USB3.1 specification with data rate up to 10Gbit/s, power up to 100W Output, audio multiplexing, and switching modes such as video signals such as DisplayPort or MHL.
So it's no surprise that hundreds of vendors are rolling out products that support USB type-c. In fact, more than 100 suppliers from many areas, from connecting cables to laptops, participated in the first USB Type-C interconnection interoperability test in July 2015 to test their products and prototypes. Interoperability was tested.
Although the industry has been dealing with USB for decades, implementing Type-C connectivity still brings many new challenges. For example, when operating at a data rate of 10 Gbit/s, the voltage swing on the data line is below 0.5V. The designer needs to implement an equalizer in the physical layer (PHY) connected to the receiving end to obtain the input signal. At this time, the "eye" in the eye diagram of the signal is basically closed, and the necessary equalization needs to be implemented to make the signal eye diagram. The "eyes" in the opening are open, and at the same time, the display signal represents logic 0 or logic 1.
There are still many other challenges when implementing Type-C connections, especially when the USB 3.1 specification works at full data rates of 10 Gbit/s.
　　 USB Type-C introduction:
1, ultra-thin
The thinner body requires a thinner port, which is one of the reasons why USB-C turned out. The USB-C port is 0.83 cm long and 0.26 cm wide. Old-fashioned USB ports are 1.4 cm long and 0.65 cm wide, which are outdated. This also means that the end of the USB-C data cable will be one-third the size of a standard USB-A data cable plug.
2, no positive and negative
Like Apple's Lightning interface, the front and back of the USB-C port are the same. This means that no matter how you insert this port, it is correct. Users don't have to worry about the pros and cons of traditional USB ports.
3, fast
In theory, the maximum transfer rate of the USB-C port is 10Gb per second. But Apple said the new MacBook's USB-C port has a maximum transfer rate of 5Gbps. The maximum output voltage is 20 volts to speed up charging time. The USB-A type has a limit transmission rate of 5 Gbps and an output voltage of 5 volts.
4, all-rounder
The new MacBook's USB-C port can transfer data, charge it, or link to an external display device as a video output port. The only question is how Apple meets users who want to do these three things at the same time.
5, two-way
Unlike the old USB port, the USB Type-C can only transmit in one direction. The power transfer of the USB-C port is bidirectional, which means it can have two transmit power modes. Therefore, the user can not only use the notebook to charge the mobile device, but also use other devices or mobile power to charge the notebook.
6, backward compatible
USB-C is compatible with older USB standards, but users need to purchase an additional adapter to complete the compatibility. Apple said that not only Apple will sell adapters, but third-party companies can also license production.
What issues should I pay attention to when developing USB Type-C?
Rethink PHY
For example, the forward and reverse plug-in nature of a connector requires reconfiguration of the physical layer in the implementation. When operating at a USB 2.0 data rate, the designer can use a pair of resistors to short the two data paths into the physical layer to indicate how the connector is plugged in. At lower USB 2.0 data rates, the physical layer has enough performance margin to handle the reflections caused by shorted data paths.
For USB 3.0 and USB 3.1 data rates, designers need to implement two data paths to handle higher rates. With one connector in one direction, the system is connected to one data path, while in the other direction, the system is connected to another data path. A dual data path is necessary because when transmitting at 5 Gbit/s and 10 Gbit/s data rates, singularity by shorting the data path will cause too much signal reflection, which will decompose the data.
The designer needs to decide how to solve this problem. One solution is to use two physical layers with one physical layer in each direction. The disadvantage of the dual physical layer solution is that it takes up 20% to 25% of the extra area to implement two SuperSpeed ​​data paths and two Hi-Speed ​​data paths, and requires two sets of phase-locked loop circuits. (PLL) and two sets of power, ground, and data pins. The end result is a system-owned High-Speed ​​data path that is one more than its actual needs.
A more efficient implementation is to use a physical layer that has been optimized for the USB Type-C specification. It has two SuperSpeed ​​data paths, a Hi-Speed ​​data path, and a set of phase locks. Loop circuit and a set of power, ground, and data pins.
Which implementation method designers choose depends on their end application. The cost-sensitive market will choose to save space and chips by eliminating an extra Hi-Speed ​​data path and reducing the number of pins by up to 40%.
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