Video data rates have quadrupled in the last five years. To support these data rates the bandwidths of transmission media needs to keep pace. For example the current HDMI video standard requires that a cable is capable of transmitting at 10.2Gbps. This data rate, with a bit time of 297 Pico-seconds on each of 3 channels, demands considerable performance from the cable. With this performance requirement there is an increased need for quality in the cable materials. Even more important is that there is now a requirement for in-production test and characterization to guarantee the data integrity in the cable.
In this article, we will discuss the potential defects in cable manufacturing and outline the challenges associated with doing the “In-Production Cable Test.” The existing cable test methodologies will be examined and we will show how features of a new generation of active cables can be used to facilitate Built In Self Test through semiconductor microchip technology.
An example of the resulting thinner, more flexible and higher quality active cable is shown in Figure 1.
Figure 1: Sample Active HDMI C to A Cable
Difference between Active Cables & Passive Cables
Passive cables are the standard in today’s cable market; they are comprised of several insulated wires surrounded by an outer coating with connectors at each end. Active cables are an evolution of these cables in that they add an integrated circuit to the passive cable.
The principal purpose of this integrated circuit is to offset the naturally occurring losses in the passive cable. This active boosting means that active cables can be more compact, thinner, longer and faster than their passive equivalents.
Figure 2a: Active HDMI Cable with exposed connectors
Figure 2a (above) shows an Active HDMI Cable with exposed connectors. Close examination reveals that there is an integrated circuit on only one end of the cable. This is because the high-speed channels in HDMI are unidirectional and the lossy signal will also need boosting at the same end of the cable.
Figure 2b: Active HDMI Cable with exposed connectors
In cables like USB3 cables there will be two active ends, as the cable is bi-directional. Figure 2b (below) is a close up of the active end of an HDMI cable is also shown to more clearly show the IC.
Potential Defects in Cables
When manufacturing any kind of component, there are always defects. Good process engineering will greatly reduce the probability of the magnitude of the defects impacting the quality of the product. It is also important to understand that today’s high speed interconnects are complex constructions. USB, Infiniband and HDMI cables don’t just have a single wire covered in an insulated coating. They can have as many as 20 individual wires inside the cable.
Figure 3: HDMI Cable Stripped back(top) and Connector (below)
Figure 3 shows an HDMI cable with exposed wires. The cable is made up of several individual wires. Any defect with these wires can render the cable non-functional or limit its performance.
NEXT: Sources of Catastrophic Error
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