Background:

The High Definition TV “experience” continues to drive manufacturers to offer truly digital devices. The days of analog video interfaces are limited. In previous articles, we touched on HDMI connections. It is clear that HD sources such as DVD players, Cable settop boxes, satellite boxes are transitioning to the HDMI standard. It is inevitable that future HD sources such as HD DVD players (HD or Blue 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.

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. 2 port HDMI switches will be 100% occupied as most HD hometheaters will use a HD cable or satellite receiver and a HD DVD player. With a plethora of HDMI sources, for example PS3, Blu-Ray, HD DVD, Apple TV, and HD video cards coming to market, it is prudent to have at least 3 HDMI inputs available to your HDTV.

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 transparency: any switch must pass HDCP data between source and monitor.

-HDMI 1.3: HDMI 1.3 is recommended since it is the latest version of HDMI. This will ensure that you protect your investment and have the bandwidth to support future applications.

- 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.

- External Powering: It is important that the HDMI switch is powered independently from a dedicated power source. Some HDMI switchers are powered directly from the HDMI cable to save cost, however this could load down the power from the HDMI source. The power carried on the HDMI cable is intended to power the internal EDID PROM inside the TV which stores the TV's capabilities. It is not intended to power up external devices.

All Octava HDMI switches utilize a dedicated power adapter.

- Intelligent Input Selection: HDMI sources provide a signal to indicate that it is available. These inputs can be utilized to intelligently select the HDMI source that the user intends to view. Octava HDMI switches use this in a SMART SCAN feature to minimize users from having to manually select the HDMI source.

-Power saving feature: Look for an energy smart device that conserves power. Although Octava HDMI switches are low power, it utilizes a Smart standby feature that automatically puts the HDMI switch into a Standby mode to conserve power when the Video Sources are turned off. We do our part to combat global warming.

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

What is a HDMI Cross Switch with Dual Ouputs:

HD systms with 2 HDTV displays will need the flexibility to route the video source to either HD display. For example, the systems consists of a DLP projector and a secondary Plasma or LCD display. A 3x2 HDMI cross switch has 3 inputs and 2 HDMI outputs allows the user to easily switch the HDMI source to either Output. Or display a separate HD stream on both displays for "picture by picture" effect.

The ability to switch the HDMI source to either output allows the user to save on projector bulb wear because the user can easily switch to the projector for movies or weekend viewing only and switch "day to day" programming to the Plasma or LCD.

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 ½ 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:

Impedance Match:
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.

The ultimate test for signal integrity is a EYE Pattern test. A "open" EYE pattern ensures that the signal at the HDTV receiver can correctly decipher the digital signal for error free signaling. For example, if a "1" is sent from the transmitter ( HD source) then the HDTV will receive a "1" . A "shut" EYE pattern that has been degraded will cause the HDTV receiver to misinterpret the digital sequence and will generate "bit errors" ( a "1" may be interpreted as a "0") which manifests itself in incorrect pixel display on the screen. A completely "closed" eye pattern will be unrecoverable at the HDTV and render the picture un-viewable.

Octava HDMI switch uses active compensation electronics to correct signal degradation to ensure a pristine EYE Pattern for error free transmisssion.

Conclusion:

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.