3 Thunderbolt interface
3.2 Interface architecture

Architecture of Thunderbolt interface is based in two perspective standards. The first is the standard PCI-E and the second is standard DP.

The advantage of PCI-E bus is its universality, a wide application in existing computers like PC (Personal Computer), a large number of technologies designed especially for the connection and cooperation with the PCI-E bus and possibility of direct connection with the PCI-E bus located on motherboard of PC.

The advantage of DP port is ability to achieve even higher than Full HD resolution (for example 4K or 5K) with still increasing frame rate. The image can be simultaneously transmitted with 8-channel audio too.

Physical Mini DP connector is backward compatible with the standard DP port. The maximum transfer rate of DP port is 5.4 Gbit/s using four links. The transfer rate is increased up to 10 Gbit/s when we connects our traffic to device with TB interface. The total transfer rate of the bidirectional two-channel transmission is therefore 20 Gbit/s.

Block diagram of the architecture of Thunderbolt interface is shown below.

image
Architecture of Thunderbolt interface

Data from DP port and PCI-E bus come into TB controller. TB controller combines the data into packets which are transmitted together via a single active TB cable.

However utilization of active cables have unfavorable thermal effects. We can measure on connected idle connector the temperature around 43°C. The temperature in the active state may quickly rise up to 50°C. The temperature on the cable between connectors is not different from the surrounding environment.

Heating of cable ends, i.e. connectors, is caused by mounting of the chip Gennum GN2033 directly into the connectors. This chip despite its very small size can provide conditions for high-speed and error-free data transmission via a thin copper pair. The chip is not directly necessary for the TB technology, but its presence improves transfer rates and the transmission characteristics of the interface. Its integration is not necessary when moving the interface into the optical cables.

Raised temperatures are not harmful to the user, but certainly contribute to the overall heating of the device and thus to higher demands on its cooling. For example, connectors for USB 3.0 interface don’t have a similar problem, because their temperature is only slightly different from the temperature of surrounding environment.

The utilization of active cables have for the user much greater impact, besides a large heating, which is a higher purchase price compared to competing types of interfaces.