Get A Better TV Picture With HDMI
By David Richards | Saturday | 24/02/2007
The big buzz with sellers of HD TV is the need for HDMI .The High Definition TV "experience" they claim is better by using HDMI cables. But the problem is that a lot of devices only come with one HDMI input and the cables are expensive, however HDMI connectivity is getting cheaper.
It used to be that you'd have to pay exorbitant prices for anything with HDMI stamped on itâ€”routing that digital video (up to 1080p) and audio at the same time must be incredibly expensive, right? But HDMI cables sold by unscrupulous retailers for 10 times more than they're really worth still carry digital audio and video from one place to another the same way the cheap ones do.
The days of analog video interfaces are limited. In previous articles, we have touched on HDMI connections. It is clear that HD sources such as DVD players, cable set-top boxes and satellite boxes are transitioning to the HDMI standard. It is inevitable that future HD sources such as HD DVD players (HD or Blu-ray), and video game stations will utilize HDMI as the interface standard. With all these new HDMI source, how does one get the desired input to the HD monitor? In this article, we will get into the details of such a device: the HDMI switch.
If you want to go HDMI you won't have to pay an arm and a leg for the privilege, but most televisions only have one HDMI-in port. What happens if you want to plug in your games console as well as another HDMI device.
Gizmodo recently reported that as HDMI cables and their associated switches get to be more commonplace, honest purveyors of electronics accessories are stepping in with prices that are more in line with reality. Case in point: Less than a year ago, a 3x1 HDMI switch with a remote control was selling for upwards of $200. Now you can get one from Monoprice that's been favorably reviewed for $63.75. For bare-bones switching, a 2x1 manual switch from Monoprice (pictured above) is now down to $28.93. Now yer talkin'.
Are there really that many devices out there that use HDMI? I'm not sure how many of us have the need to switch between multiple HDMI inputs, but it's nice knowing that if the standard becomes widely adopted for more electronics, we'll have a few products that will let us use our devices without having to take out a second mortgage on our homes.
What is a HDMI switch:
A HDMI switch allows the end user to select multiple HDMI sources, such as DVD players, settop boxes, into 1 HD monitor. The basic models available are 3x1 HDMI switch, which simply means that there are 3 inputs and 1 output. The 3X1 HDMI switch allows the user to switch between 3 HDMI sources. There are also 5x1 HDMI switches available which allows the user to select up to 5 HDMI sources. By the way, we highly encourage users to select at least a 3 port model for future expandability.
Why do I need a HDMI switch: Anyone who has a HD monitor with less than the desired number of HDMI inputs can use an external HDMI switch to expand the system.
What features do I look for in a HDMI switch:
-Expandability: 5 port HDMI switch is recommended for future expandability. If you use a 2 port, then you have no expandability. It is likely that future HD sources such as games stations, HD DVD player/recorders will utilize HDMI.
-HDCP transparancy: any switch must pass HDCP data between source and monitor.
- Backward compatibility with DVI-D: There is a mix of both HDMI and DVI-D devices in the field. Users should select a HDMI switch rather than a DVI-D switch since HDMI is backward compatible with DVI-D. With a HDMI switch., the user just chooses the correct cables needed; either HDMI or HDMI to DVI-D to customize to your system.
- Remote control: A remote control to select the desired channel is essential.
What is a HDMI switch with Toslink Routing:
Many consumers who recently purchased a HD Display and especially those who are installing front -projector systems already have an existing Surround Sound Audio Receiver that need to be converted to one with HDMI switching functions.
For those seeking to integrate with their existing Surround Sound Audio Receivers, the 4x1 HDMI switch with TOSLINK Routing can be used to accomplish this. This easy to use unit includes 4 HDMI Inputs and also Optical Digital Audio switching for maximum port expansion and integration with existing audio video receivers
Design consideration of a HDMI switch:
HDMI is extremely high speed digital transmission standard with an aggregate data rate of ~4.95 Gbps. Jean Baptiste Fourier (1768-1830) showed that any signal waveform can be resolved into a summation of harmonically related sine waves. The amplitude of the sine waves can be determined by calculation of Fourier transforms.
So what in the world does some dead French mathematician have to do with the HDMI switch? Well, Fourier tells us that the waveform is a summation of harmonically related sine waves. Therefore, higher data rate, higher frequency sine waves. Incidentally, the frequency of the fundamental sine wave is Â½ of the data rate. For example, the fundamental frequency of a 2 Gbps ( 50 % duty cycle ) square wave is 1GHz.
As data rates increase, every aspect of the switch design (every millimeter) becomes critical because the wavelengths of the signals approach the size of the components on board. The 3 critical parameters to consider are:
HDMI is based on a 100 ohm (differential) impedance. It is imperative that the switch be optimized to match this characteristic impedance. Any imperfections of the board layout will cause "reflections" which degrades signal transmission to the HD monitor. Think of "reflections" as signals that are lost between the inputs to the output. Utilizing careful RF and Microwave layout techniques minimizes these reflections.
Minimum Insertion Loss:
Signal loss should be minimized in order to maximize signal integrity to the output of the HDMI switch. Again, utilizing careful RF and Microwave layout techniques minimizes insertion loss.
Minimum Cross Talk:
With multiple inputs (up to 4), all potentially being active at same time, it is imperative that the desired channel not be interfered from any undesired channels. Again, careful RF microwave design techniques minimize cross talk.
HDTV technology is changing rapidly. HD connections such as HDMI will become the de facto standard in HDTV connections. With increased HDM sources, an external HDMI switch will be needed in order for the user to select the desired input. We have outlined the important features of a good HDMI switch , along with the design considerations involved.
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