The Copper Cable Limitations

Having extremely high resolution displays and image sensors creates a new set of challenges for system designers. There are many challenges involved in transporting such huge amounts of data to and from displays and image sensors in these applications.

To handle the ultra-high-speed data transfers associated with these 4K and 8K resolution displays and cameras, as well as the high-speed data transfers needed to store 4K content, several new high-speed consumer standards have been developed. However, a major problem has been identified – as the speed of these interfaces increases, the traditional copper cables used to transmit data become shorter, thicker and heavier.

Cable length and thickness limitations :

The above graphic shows how copper cable length decreases as the data rate increases. In contrast, the length of optical cables is not limited no matter how high the data rate.

The above graphic shows copper cable thickness (and therefore weight) increases with data rate. In contrast, optical cable thickness remains the same (ultra-thin) no matter how high the data rate.

Copper cables are available for this new generation of high-speed interfaces, but they are thick, heavy, bulky, and limited to about 1 meter in length. This is not acceptable to consumers. The copper cable has reached its limits and a new solution is required.

Signal Losses in Copper Cables Increase as the Data Rate Increases

For a given length and wire thickness of copper cable, the signal loss increase dramatically as the data rate increases. At a certain data rate, there is actually no usable signal coming out of the end of the cable! This can be mitigated to some extent by using pre-emphasis and equalization techniques, such as those built into HDMI, DisplayPort, and USB 3 standards. However, as the data rate increases, these techniques become ineffective. The only solution is to increase the thickness (AWG) of the copper wires used inside the cable to compensate for the signal loss. This causes the copper cable to become thicker, heavier, and less flexible, and also increases the cost of the cable. As an example, a copper cable operating at 10 Gbps or 12 Gbps can easily be up to 8 mm in diameter with a cable length of only 3 m or less.

Active Copper Cables also have their Limitations

Active copper technology was developed to address the limitations of passive copper cables at high data rates. This technology involves adding semiconductors inside the cable to further boost and equalize the signal. This results in slightly longer and thinner cables, but it has its limitations. These types of cables are power-hungry and can only extend the length of the copper cable for a short distance. They also cannot operate at higher data rates.

Wireless Doesn’t Work Either

Several wireless standards (Wireless HD, Ultragig, etc.) have been developed in an attempt to eliminate the need for copper cables. However, they all have the same limitations. They have a maximum total data rate of around 7 to 10 Gbps, which is only adequate for the old 1080p HD resolution, not today’s 4K UHD, and certainly not 8K. In addition, they have very high latency, which rules them out for gaming. They are costly and power-hungry, and they also require a line of sight (so don’t walk between the wireless transmitter and your TV, otherwise there will be a dropped picture!). Therefore, wireless technology is not suitable for these new high-speed consumer interfaces.