HDMI-to-VGA converter

HDMI-to-VGA converter

In an ideal world, a HDMI-to-VGA converter would not be needed. The best option would be to only have HDMI compatible devices, in which case, we can simply use a HDMI-to-HDMI cable to connect them up. However, currently, we do not have that. Truth is, HDMI is a relatively new standard (V1.0 released around 2003) so there are a lot of older devices that do not have HDMI ports (or even DVI ports for that matter). One such example is older computers and display monitors that have VGA ports. Therefore, if you have a newer device that only has HDMI ports and you would like to connect it to an older monitor you would need a converter cable. In this case, a HDMI-to-VGA would fit the bill.

Obviously, with this arrangement there will be some lost in quality of the content that is displayed. But, depending on the objective that you are trying to achieve, that might be acceptable. Even in a pure HDMI eco-system, the maximum HDMI functionality and benefit is determined by the device with the minimal amount of HDMI functions. The same rule applies to any HDMI-to-other_format converter.

The above example highlights the HDMI-to-VGA cable, but, I suppose the reverse connection — VGA-to-HDMI is also possible. A computer with a VGA port that connects to a HDTV with a HDMI port for example. In any event, the same limitations applies ! If both of the devices that you are trying to connect have VGA ports, then use them and a regular VGA cable. You will NOT gain any benefits by using a HDMI-to-VGA cable when you have the aforementioned VGA-to-VGA scenario.

So, what are some of the technical differences between a HDMI and a VGA connector ?

The explanation will get a little more technical, so I will explain it in the “Tech Talk” section below.

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To start, the pin count between the two connectors are different. The VGA port has 15-pins while the HDMI port has 19. Fundamentally, the VGA port is an ANALOG device that uses analog signals to communicate. HDMI is all DIGITAL. Consequently, for a HDMI-to-VGA converters, DIGITAL signals are being converted into ANALOG signals using what is known in the Electronic Engineering world as an Digital-to-Analog (DAC) converter. For the reverse connection VGA-to-HDMI, the reverse conversion with an electronic device called a Analog-to-Digital (ADC) converter is used.

By-the-way, if you don’t know, and you are wondering what is ANALOG and DIGITAL ? Basically, an ANALOG voltage signal is a signal that can be any voltage value (an infinite amount of different possibilities) between some low and high threshold. For example, if the low threshold is 2 volts and the high threshold is 5 volts, the analog signal can be any value within that range.

Unlike the ANALOG signal, the DIGITAL signal is essentially limited to only two values: 0, 1 — where the “1″ is actually an abstraction of some set analog voltage (i.e. 3 volts). For obvious reason, a DIGITAL signal is usually much easier to process and manipulate. Which probably explain why we are currently living in the digital age. There are some other technological factors for why digital is so ubiquitous but, I won’t get into that at this time.


What is High Definition ?

The “HD” of HDMI means High Definition (AKA: High Def). But, what exactly is that? It is synonymous with top quality. The meaning is not really black and white .. yeah, it is more like a shade of gray. It can also be used in different contexts: sound, video, broadcast, antenna, cable, display, and so forth. For this entry I will focus on display as in the case of a HD TV and to some extent, HDMI cables.

Fundamentally, in the context of displays, High Definition simply means higher than standard resolution for video. Think of a TV or a computer monitor as a rectangle with a certain number of Horizontal and Vertical lines (or pixels). The resolution of the display is determined by the number of lines in both directions. The more lines there are, the higher the display resolution.

So, what is standard resolution? Actually, it depends on where you are. From the European developed PAL and SECAM system, it is 576i lines. For the American National Television System Committee (NTSC), it is 480i.

As a general matter, the characteristics of a HD display is captured with the following 3 properties:

Frame Size – is defined as the number of Horizontal pixels by number of Vertical pixels. For example, one common Frame Size is: 1280X720

Scanning System – usually represented with a symbol of “p” or “i” for Progressive and Interlaced scanning respectively. These are technical sounding terms, but they are pertinent to the understanding of different types of displays. Progressive scan is a way of displaying and manipulating images in which all the lines of each frame are drawn sequentially. Basically, it is like reading a page of a book from the upper left hand corner to the lower right hand corner without skipping a line. The benefit of this way of scanning is that motion appear smoother and more realistic. It is also better for up-scaling to a higher resolution. The only negative about this method is that it requires a higher bandwidth which has many implications all of which broils down to higher cost in the final analysis.

With Interlaced scanning, odd lines and then even lines of each frame are drawn alternatively. However, the characteristics of the display material and the responsiveness of the human eyes create the perception of a continuous image. This is the method that is used in most analog systems. The benefit of this method is that it requires less bandwidth. In fact, ½ as much as compared to the Progressive scan method. The drawback is that the picture quality is not as good.

Frame Rate – as the name suggest, is the number of video frames per second. For most modern HD TV this is on the order of 60 to 120.

Sometimes all three properties are specified in this format:

[Frame Size][Scanning System][Frame Rate]

 However, more times than not, some of the details are dropped because they are implied. So, in marketing literature and commercial naming you will most likely see something of this form: 720i, 720p, 1080i, 1080p

In this form, only the Vertical Resolution along with the Scanning System is specified. When you go to your favorite electronic store or shop online, this is the form that you would see.

For connecting HDMI enabled devices to High Definition (HD) displays with resolutions of: 720i, 720p and 1080i a Standard HDMI® Cable should do the trick. However, for a 1080p display a High Speed HDMI® Cable is recommended.