Today mobile devices in the form of smartphones and tablets are becoming more and more "smart", and many of them are not inferior in functionality even to powerful computer systems. And, interestingly, most of the new devices support MHL technology. To connect gadgets to TV panels and the feasibility of using such innovations, it is important to understand what the essence of MHL is.
MHL technology: what is it?
In general, the abbreviation MHL stands for Mobile High-Definition Link (almost HDMI), which, in ordinary language, can be interpreted as a technology for mirroring the screen of a mobile device on a high-definition television panel. It appeared relatively recently, so even the declared support for MHL in some devices may not work. Today, the most widespread and used are MHL versions 1.x and 2.x, and only recently the third version has appeared, which, although it has quite high prospects for implementation, has not yet received widespread distribution. As for the main features, the use of this screen mirroring technology allows you to transfer a Full HD image with a resolution of 1080p and 7.1 surround sound from a mobile gadget to a TV panel with minimal transmission time delays. But this only applies to the first and second versions. In the third modification, to the surprise of many, the ability to broadcast images in 4k (Ultra HD) format was added.
MHL versions
The MHL standard was developed in mid-2010 by a consortium of Nokia, Toshiba and Sony.
The MHL 2.0 version was released on smartphones in April 2012, increasing the power supply to 4.5 W (0.9 amperes, optionally up to 7.5 W at 1.5 A). 3D video modes were introduced (up to 1080p 24Hz 3D), the resolution was increased to 720p / 1080i 60 Hz, the MHL sideband channel (MSC) was introduced.
Version 3.0 of the MHL standard was released in 2013, it increased the maximum resolution to 2160p30, and can transmit up to 10 watts of power.
In January 2015, superMHL 1.0 was introduced, supporting in some cases formats up to 8K Ultra HD (7680 × 4320) 120Hz with HDR and 48-bit color. The standard introduces a 32-pin superMHL connector (up to 6 A / V lines, 6 Gbps each). A USB Type-C connector can also be used (with lower bandwidth, up to 4 A / V lines). The specification also supports VESA Display Stream Compression (DSC) 1.1, a video compression mechanism (up to 3 times the stream reduction). The superMHL signal source can be devices with micro-USB or proprietary connectors, HDMI Type-A is used only by the signal receiver. USB Type-C and superMHL connectors can be used in both sources and destinations.
Analogs MHL
If we consider some similar developments, it is easy to see that this technology is very much reminiscent of, say, Miracast or Intel WiDi. In mobile devices and panels, Samsung mhl is often called Screen Mirroring. This is wrong, although there is an analogy. However, the similarity in our case concerns only the principles of signal transmission, and certainly not the connection. Hence, there are cardinal differences in the basic principles that correspond to the use of MHL in practice.
The main differences between MHL and other standards
Now let's look at the well-known developments and the original MHL technology. It's easy to figure out that this is in terms of its connection principle, given that the broadcast is carried out exclusively using a wired connection like HDMI, and not using, for example, Wi-Fi connections. In other words, in order to transfer an image from a mobile device to a TV panel, you need to use special cables with adapters. This is where the new technology is very much similar to a conventional connection via an HDMI cable.
But! If a mobile device is connected either via an HDMI connector (using an adapter) or using a wireless connection, it will be discharged quickly enough when broadcasting a signal. On the other hand, MHL allows, when connected, to charge the device in the same way as it happens through connecting to USB ports. In this case, there can also be two options: either charging is done using an external source, or from the panel itself. It all depends on the type of adapter used. In addition, it is the connection of special adapters that allows the signal to be broadcast even if the MHL technology is not supported by any of the devices. And this is already a significant plus.
How is the connection made via MHL-adapter
As already mentioned, special adapters should be used for correct connection. They are distinguished by two main types: passive and active. The passive cable is very similar to standard mobile cords. On one side there is a micro-USB connector, on the other - a plug resembling a regular USB. In fact, the second connector is a standard MHL connector and must be connected to the TV panel through a dedicated jack.
If there is no such socket on the panel, it makes sense to use a passive cable, which has the same micro-USB connector (plug) and two more ports: HDMI (MHL) and a regular micro-USB input. As for charging gadgets, in the first case, a direct connection to the TV is used, in the second option it is supposed to connect an additional external source (remember how passive and active speakers for computers work). By the way, it is the presence of a passive cable that allows broadcasting on panels in which there is no MHL support.
All pros and cons
So we got to know the MHL technology a bit. What it is and why it is needed, I think, is already a little clear. Now let's look at some of its advantages and disadvantages. The first category certainly includes support for high-definition images (up to 4k), Dolby Surround 7.1 and DTS sound, as well as the ability to use multiple monitors at the same time, plus connecting a fairly large number of supported peripheral devices (mouse, keyboard, touch screens, etc.) etc.). In addition, the technology itself is based on the basic principle of Plug & Play self-adjusting devices, that is, there is no need to make settings - just plug and use. As for the shortcomings, the main problem here comes down to the fact that today there are a limited number of both mobile gadgets and TV panels that have MHL support (there is no need to talk about version 3.0 yet). Thus, most tests show that at best, you can transfer a 1080p image with a frame rate of about 50 fps. When trying to stream more video with a smoother transition at 60 fps, alas, problems very often arise. Finally, the current of 500 mA, provided in version 1.0, is clearly not enough to fully charge the mobile device and maintain all functions.
Outcome
That, perhaps, is all on the topic "MHL: what is it?" Of course, only the main aspects related to the technology itself, the principles of its use and practical application, are given here without in-depth study of the technical part of the issue. Nevertheless, it seems that even such a brief information can give an idea of how promising such a technology is, despite even a wired connection between the devices. Naturally, I would like to hope that the developers will not stop there and present the world with some innovative development on this basis, especially since wireless chargers are no longer a wonder, because it would be interesting to look at the combination of such charging with wireless image transmission.
