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HDMI Switch: Insiders Guide
 

A HDMI switch enable multiple HDMI sources to be connected to a HD display. There are different categories of HDMI switches each with special applications as listed below:

HDMI switch multi input/single output:
A HDMI switch with single output enables multiple HDMI sources, such as DVD players, settop boxes, to be switched and shared on 1 HD display. For example, a 5x1 HDMI switch, enables 5 HDMI sources to be switched and shared with a HD display as shown below.

HDMI switch connection diagram

HDMI switch with Optical Audio port:
HDMI switches may incorporate additional audio capabilities such as converting audio to an optical output.. For example, the HDS4A 4x1 HDMI audio switch with Audio provides an optical audio port for integrating sources with a surround audio system.

HDMI switch with audio output port

HDMI Distribution amp :
A HDMI Distribution amp distributes 1 video stream to multiple HD displays. All connected HD displays will view or 'mirror' the same video source. Distribution amps can be cascaded to support more displays. An 8 output distribution amp cascaded with 8 additional 8 port amp is shown below:

HDMI Distribution amp

HDMI Matrix (Multi input Multi output HDMI switch):

A HDMI matrix switch enables multiple sources to be switch and distributed to multiple displays. A matrix switch allows any combination of inputs to be switched to the display. For example a 4x4 HDMI matrix allows 4 HDMI sources to be switched to any 4 HDTV.

HDMI Matrix HDbaseT over 1 cable 200ft-HD4xSTPMX application

The following table illustrates the switch combinations of a HDMI matrix switch.

Input sources
Output Displays
Switching combinations
4x2 Matrix 4 2 4x4 = 16
4x4 Matrix 4 4 4x4x4x4 = 256
4x8 Matrix 4 8 4x4x4x4x4x4x4x4 = 65,356
8x8 Matrix 8 8 8x8x8x8x8x8x8x8 = 16,777,216

 

Features of a HDMI switch:

-Expandability: select a HDMI switch that has adequate number of inputs to connect current devices and allow for future expansions. Virtually all Video devices ( digital cameras, tablet, mobile phones) will support HDMI so it is recommended that your system include additional ports to support new devices.

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

- 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.

-EDID Management: EDID is an acronym for Extended Display Information Data.  EDID was originally implemented by computer monitors to communicate its display capabilities to the video card so a compatible video resolution could be negotiated. EDID is also used by HD Displays via HDMI to identify the HDTV display and audio capabilities to the connected video source. Basic HDMI switches with single output simply pass the EDID directly from the display to the source. For multiple output devices such as a HDMI distribution amp, or matrix switches, a method for customizing or managing EDID is recommended. EDID Management allows the user to manually select the desired EDID in order to properly operate a multi- display system which may include multiple displays and audio receivers each with differing capability.

 

Design consideration of a HDMI switch:
HDMI is extremely high speed digital transmission standard with an aggregate data rate of ~6.75 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 transmission.

HDMI degraded EYE pattern HDMI Open EYE Pattern

no active compensation
with active compensation

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.

Contact us by email at info@Octavainc.com

 

 

 

 
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7078 Peachtree Industrial Blvd. Suite 300
Phone:770-825-0388
Norcross, Ga. 30071

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