Comparison of Signal Attenuation in Long-Distance Transmission of Industrial DP and HDMI Interfaces

I. Passive copper cables, the limits of both interfaces arrive very quickly

The transmission distance of ordinary passive copper cables for both DP and HDMI is not very far. Generally speaking, the stable transmission distance of DP passive cables is around 3 to 5 meters, while the passive HDMI cables of better quality can reach about 10 meters. However, beyond this range, the signal quality begins to deteriorate. This difference is partly due to the differences in signal protocols between the two. HDMI has a certain signal compensation mechanism at the cable end, which has a slightly higher tolerance for short-distance attenuation. However, fundamentally, both are subject to physical limitations. Passive copper cables can do little in long-distance transmission.

II. Higher bandwidth leads to greater distance limitations

The higher versions of interfaces such as DP2.0 and HDMI2.1 have significantly increased bandwidth compared to the older versions. However, this comes at the cost of lower tolerance for cable losses. The critical transmission distance is actually shorter than that of the older versions. This rule was also mentioned in the previous article about long-distance transmission of DP. As the signal rate increases and the frequency components become more abundant, the high-frequency attenuation of the cable becomes more likely to become a bottleneck. A cable that works fine with DP1.4 might start to exhibit abnormal images when switched to DP2.0. In industrial settings, if equipment uses high-version interfaces, the selection of long-distance transmission solutions should be more cautious than with lower versions. One cannot simply apply the experience from the DP1.4 era directly.

III. Active Copper Cables, a Moderate Distance Transition Option

After exceeding the transmission range of passive copper cables, active copper cables are a relatively cost-effective intermediate solution. The cables are internally integrated with signal amplification and equalization chips, actively compensating for high-frequency losses, enabling the transmission distance to be extended from a few meters to tens of meters or even further. Products for DP and HDMI with active copper cables are available. These products require power supply from the host end or display end to power the internal chips. Most products solve this through the power pins of the interface itself, without the need for an additional power supply connection. The usage is similar to passive cables, except that the price is higher. In industrial sites where the distance is within 20-30 meters, active copper cables are usually a more economical choice than directly using optical fibers.

IV. Fiber Optic Solution, The True Answer for Long-Distance Transmission

When the distance exceeds 30 meters or even tens or hundreds of meters, active copper cables can no longer guarantee stable transmission. At this point, the fiber optic solution is a more suitable choice. The fiber optic extenders for DP and HDMI convert interface signals into optical signals for transmission through optical fibers, and then convert them back at the receiving end. The optical fiber transmission loss is extremely low, theoretically up to several hundred meters without any problem. Moreover, it is almost unaffected by electromagnetic interference. This characteristic is particularly valuable in industrial sites with dense frequency converters and servo drives. In this case, the product ecosystem for both interfaces is relatively complete. When selecting, the main considerations are the signal processing quality of the extenders themselves and the support for interface versions. Cheap extenders may have compatibility issues in high-resolution modes. In industrial settings, it is essential to choose products with complete specification descriptions.

V. Are there any differences in attenuation performance between DP and HDMI at the same distance

When strictly comparing the differences in long-distance attenuation characteristics of the same version and the same cable specifications, there are actually no particularly significant fundamental differences. Because both are high-speed differential signal transmission, the physical attenuation mechanism is similar. The differences actually observed in actual use are more related to the specific product's cable manufacturing process, interface version, and the receiving end's signal tolerance, rather than the fundamental differences in the physical signals of DP and HDMI protocols. Therefore, when choosing a long-distance solution, there is no need to worry about which protocol is more resistant to attenuation. What should be focused on is whether there are suitable active copper cables or fiber optic extenders, and the actual support of these products for the current interface version.

VI. The attenuation problem is exacerbated by industrial interference

The attenuation of signals in laboratory conditions and actual industrial environments may differ significantly. When interference sources such as frequency converters and servo drives are added to the industrial site, the distance that could be transmitted under test conditions may fail in the actual site. In this case, the shielding quality of the cable is crucial. Cables without proper shielding layers will not only amplify the normal signal but also the interference, resulting in a worse effect.

VII. Link Budgeting - A Necessary Step Before Selecting the Long-Distance Solution

Regardless of whether you choose an active copper cable or fiber optic solution, it is recommended to conduct a link budgeting before placing an order. Put together the variables such as the actual transmission distance, target resolution refresh rate, and on-site interference conditions for evaluation. Confirm that the selected solution has sufficient margin to handle the actual working conditions. Even if the selected solution seems to work just fine, as the equipment ages a little or the environment changes a bit, intermittent image abnormalities may start to occur. Such problems are the most difficult to troubleshoot because there are no obvious fault points; it is merely an occasional problem caused by the overall insufficient margin.