What are Active & Passive Adapters/Cables and How to Distinguish Them?

In the previous article, we mentioned active USB extension cables and passive extension cables. In fact, there are also active and passive video adapters, such as DP/mini DP to HDMI/VGA adapters. So what is the difference between active and passive adapters/cables? How can we distinguish them?

What is a Passive Adapter/Cable?

A passive cable is a finished cable that you make by using some wires to join the pins of the two plug ends together, without any signal boosting capabilities. Passive cables/adapters will be cheaper because they don't need to feature extra chips. Most of the cables we buy for home use are passive. In general, passive cables designed to exceed the maximum distance recommendations will have thicker wires and better shielding, which helps extend the USB signal further than "standard" cables.

If you want to send DisplayPort or Mini DisplayPort signals from a computer or other video source to a VGA, DVI, or HDMI monitor, you’ll need an adapter/converter. Choosing an active or passive adapter depends on the type of signal from your video source, the number of monitors you are using, and whether your video source supports dual-mode DisplayPort (DP++) output.

Looking for a DP++ symbol above a DisplayPort or Mini DisplayPort source is a quick way to see if a passive adapter can be used. If your video source supports DP++ output, you can use a passive adapter to send DisplayPort video to a single-link DVI or HDMI display. The DP++ video source performs the conversion instead of the adapter. By the way, the Thunderbolt port natively supports DP++. If the source does not support DP++ or you want to connect to multiple monitors, you may need an active adapter.

What is an Active Adapter/Cable?

Active cables use built-in powered circuitry (additional chips) to maintain and boost the data signal with perfect reliability, helping to keep the integrity of the data it’s carrying over longer distances. And its transmission distance is longer than a passive cable. Active adapters/converters also use an extra chip to convert single-mode and dual-mode outputs inside the adapters, so the video source you connect doesn't have to support DP++. That is to say, the adapter performs the conversion from DisplayPort to VGA, DVI, or HDMI, not the source device.

Active adapters are ideal for use with graphics cards such as AMD Eyefinity that do not output dual-mode signals. If you want to use multiple monitors on the same computer, you should use an active adapter, as some graphics cards cannot run the maximum number of monitors when using DP++. This is especially true if the computer has multiple DisplayPort or Mini DisplayPort connections.

By the way, USB-to-serial is usually not a passive adapter because the simple fact is that 5V USB is not compatible with 9-12V TTL serial. Therefore, a USB serial adapter will have at least one level shifter to amplify the signal going out through the serial and attenuate the serial signal coming in.

How can I Tell if the Adapter/Cable is Active or Passive?

Generally speaking, if the adapter or USB extension cable is active, the seller will usually indicate it, like CableCreation active USB extension cable or active DisplayPort to HDMI adapter. And most of these accessories will have a small box that can accommodate the conversion chip, and the part will be larger than the ordinary plug. If the adapter cable is no bigger than a regular plug, it's most likely passive. All DisplayPort to VGA adapters are active because DisplayPort uses digital signals and VGA uses analog signals. DisplayPort to HDMI/DVI adapters can be active or passive. All in all, Active adapters/cables have a chip to increase the performance of that device. If there is no chip, the adapter is considered passive.

It's important to note that if you want to take advantage of DisplayPort technology (such as AMD Eyefinity technology) when connecting a DVI monitor to the GPU's DisplayPort port, you'll need an active adapter, as an active adapter can convert the monitor's DVI signal into the GPU's native DisplayPort signal. That is important for AMD Eyefinity because the GPU can synchronize DisplayPort signals to keep all monitors moving in concert. Passive adapters can only help the DisplayPort output communicate with the "language" of DVI. As far as the GPU is concerned, it is not connected to a DisplayPort display. You can check with your graphics card manufacturer to confirm what type of adapter is required for the setup you want to run.