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HDMI:
Guide To HDTV Connection Of The Future
By: Jeff Su
Background:
As the HDTV market continues to heat up, consumers are in need of
being educated on the latest technology. One of the terms that you, the
consumer, will surely run into while selecting a HDTV set is:
HDMI.
For most this is an
unfamiliar term and we will explain the details of HDMI in this
article so you, the consumer, is armed with the proper knowledge to make
intelligent purchasing decisions. |
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What is HDMI:
HDMI is an acronym for High Definition Multi-Media Interface. The
HDMI specification (now at 1.2) was created by some of the largest
consumer electronics manufacturers in the world: Hitachi, Matsushita,
Philips, Silicon Image, Sony, Thomson, and Toshiba. HDMI is the
latest digital HDTV interconnection standard. The notable
differences between HDMI and the earlier HDTV interconnects standards
(component video, and DVI) are: |
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-HDMI is all digital unlike analog
component video cables
-HDMI supports multi-channel audio in addition to digital video. (DVI
only supports digital video)
- HDMI is more compact in size and carries both audio and video
signals therefore eliminate cable clutter.
-HDMI incorporates content protection called HDCP ( high definition
content protection)
What does a HDMI connector look like: HDMI looks similar to a USB
cable. The compact size and high integration (carries both audio and
video) makes the HDTV installation experience truly "plug and play."
Why should I use HDMI:
-HDMI is all digital, so picture quality is "perfect" from source to
display
-HDMI is both a digital audio and video connection. This will minimize
cabling in your system
-HDMI is rapidly becoming the de facto standard for HDTV connections.
How does HDMI transport the digital video: The video portion of HDMI
is carried by 3 separate differential pairs. Each pair transports 1 of
3 uncompressed native digital R,G, B signals from source ( dvd
player,set top box) to the sink ( HDTV display). A unique protocol,
T.M.D.S.( transmission minimized differential signaling), is used to
transport the digital data. Each pixel is represented by 24 bits ( 8
bits each for each of the primary colors). The T.M.D.S. protocol then
"calculates" and stuffs 2 extra bits to the video data stream in order
to create a digital stream with minimum transitions ( lower EMI, lower
interference) and also minimize long strings of '1' and '0' which can
cause detection errors.
A fourth differential pair, called the TMDS clock provides the pixel
clock for timing the data stream. The maximum TMDS single link pixel
clock rate is 165 MHz.
What is the data rate of a single link HDMI connection: The maximum
pixel clock rate is 165MHz and each of the 3 TMDS video streams
carries 10 bits. Therefore the aggregate data rate is 3 x 10 x 165MHz
= 4.96Gbps.
How many pins are included in the HDMI connector: There are 19
individual pins in the HDMI connector. There are 3 pairs of TMDS
signals which carry all the digital audio and video signals.
How is the digital Audio signal transported: The multi-channel audio
is time multiplexed into the TMDS data streams. Audio is much lower
data rate (192kbps) and the extra time is used to demux the audio
signals.
What is HDCP: HDCP is an acronym for High-Bandwidth Digital Content
Protection. HDCP is an encryption method developed by Intel in order
to control unauthorized copying of digital media. The encryption is
carried out in the HDMI transmitter found in the "source" ( dvd
player, set top box) and decryption is carried out by the HDMI
receiver ( the HDTV display). The secret keys for encryption are
exchanged between the source and display over an I2C bus ( pins 15 and
16).
Is HDMI compatible with DVI: DVI is the predecessor to HDMI. HDMI and
DVI are identical as far as video is concerned. Therefore, video
backward compatibility exists. However, DVI will not support digital
audio. For example, if you have an older DVI connection on your source
and a HDMI connector on your display, a HDMI to DVI cable is all that
is needed in order to view the video. A separate audio cable ( TOSLINK
or SPDIF) will be needed to carry the digital audio.
What formats will HDMI support: HDMI is high speed digital connection
and will support resolutions of 480i, 480P, 720i, 720 P, 1080i and in
the future,1080P.
Conclusion:
HDTV technology is changing rapidly. HD connections such as
HDMI will become the de facto standard in HDTV connections. We
have outlined the important features of HDMI, so the consumer is well
informed and ready to make intelligent purchasing decisions.
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About the Author:
Jeff Su is product development manager at
http://www.octavainc.com. He can be reached at info@octavainc.com
Read more articles by:
Jeff Su
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HDMI | HDMI Cables | DVI to
HDMI Cables | HDMICable | HDMI DVI Cable
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