Volume 45 – February 2011
article in PDF format. (667KB)
HDMI Transceivers Simplify the Design of Home
that large-screen HDTVs (high-definition televisions) have achieved
widespread acceptance, many consumers are expanding their electronics
collection to include components for a complete home theater system.
Home theater in a box (HTiB), sound bars, and audio/video
receivers (AVRs) enhance the user experience with superb audio while
complementing the HDTV video performance. The ability to extract and
process high-fidelity audio signals is a key differentiator among the
hardware choices on the market today. Home theater systems can now offer
all the latest features of the High-Definition Multimedia Interface
integrated within the equipment.
effort to improve the home theater experience comes with several implementation
challenges for the system designer of HTiBs, sound bars, and AVRs.
The latest version of the HDMI standard includes new optional features,
such as an audio return channel (ARC), 3D display formats,
and enhancements to the consumer electronics control (CEC)
protocol. Consumers, of course, want their new home theater equipment
to include all of these new HDMI featuresat lower cost and with
more user-friendly controls. Designers of home theater equipment must
thus adapt to the new standards, while shrinking their bill-of-material
(BOM) costs, development costs, and time to market. To help designers
meet these challenges, Analog Devices has created HDMI transceiver
products that incorporate these new features.
example of an HDMI transceiver is the
which incorporates a 4:1 HDMI input multiplexer (mux), HDMI
receiver, on-screen-display (OSD) engine, and HDMI transmitter.
Individually, these functions would require discrete ICs, each with
its own unique firmware, but a transceiver can combine all these functions
in a comprehensive solution, reducing board area, firmware complexity,
and BOM costs for the home-theater system designer.
1. Functional block diagram of an HDMI transceiver.
Theater in a Box
are complete video playback systems. They generally include a multichannel
audio amplifier and a surround-sound speaker system for playback of
audio. In addition, they usually include a DVD or Blu-ray™ video player.
HTiBs ease installation and power matching between the video player,
amplifier, and speakers. HTiBs principally process audio; the video
is passed through to the TV over the HDMI interface. Figure 2 depicts
a typical HTiB system.
2. Block diagram of a typical HTiB system.
the increased popularity of thin, large screen, flat panel TVs, sound
bars are emerging as complementary AV systems. These are compact,
easy-to-set-up speaker systems that provide much better sound quality
than the TV speakers. Since most HTiBs and sound bars are used with
large-screen HDTVs, their audio and video connectors mainly utilize
HDMI. A typical sound bar will have multiple HDMI inputs to handle
various sources, a single HDMI output for the connected TV, built-in
audio processing, and speakers. Figure 3 illustrates a typical sound-bar
3. Block diagram of a typical sound bar with HDMI hub.
sound bars comprise multiple speakers and amplifiers with surround-sound
decoding capability. Their electronic and acoustic design features
can produce a surround-sound effect without separate speakers at the
back of a room. Middle- to high-end sound-bar systems often contain
DVD or Blu-ray players, resulting in system architecture similar to
that of HTiBs.
Return Channel (ARC)
new feature in the HDMI specification provides for an audio return
channel (ARC)to allow the HTiB to process audio from the
downstream device. In order to listen to the TV audio without an ARC,
an independent cable (optical S/PDIF or coaxial) would be required
to send the audio from the TV or tuner back to the HTiB. With the
ARC, the HDMI cable can return 2-channel S/PDIF or multichannel
audio from the TV back to the HTiB, dispensing with the extra audio
cable. HDMI transceivers offer an ARC receiver on the HDMI output
adds significant value in the case where the TV, set-top box, or other
downstream HDMI sink device uses a tuner to receive new media content.
Instead of listening to the audio over the less powerful internal
TV speakers, the user can easily employ the higher fidelity HTiB system
output. The returned audio data passes on the HDMI cable from the
TV to the HTiBin the opposite direction to the traditional
video data pathwithout regard to whether or not the video output
to the HTiB is active on the cable.
Display Identification Data (EDID) Replication
transceivers provide an EDID replication feature that reproduces a
single location memory across multiple HDMI portseven when the
HTiB is in power-down mode. This enables faster system start-up times,
as all of the upstream HDMI source devices can configure their video
outputs properly before the HTiB is powered up. The only power required
for EDID replication is furnished by the +5 V/55 mA available from
the source via the HDMI cable.
a bridge between 3D content-providing sources, such as game consoles,
Blu-ray players, and 3D-capable TVs, HTiB manufacturers must stay
ahead of the technology curve to enable customers to benefit in the
long term from the full range of features offered by their source
and sink devices. HDMI transceivers that incorporate the latest versions
of HDMI technology support implementation of 3D video as part of the
home theater experience. This new feature of the HDMI standard significantly
enhances the user experience; such features are critical to energizing
specification defines an infrastructure for communicating 3D video
in the home via a list of mandatory and optional video formats. In
a practical application, the HTiB must present to the connected sources
a list of supported 3D formatsretrieved from the connected TV
and parsed against its own list of supported 3D formats. The connected
source then indicates to the HTiBthrough HDMI protocol commandswhen
it is sending 3D content. The HTiB can then extract and output advanced
audio formats, such as Dolby TrueHD® or DTS-HD
Master Audio®, that were
sent over the HDMI link, but that the TV may not be equipped to support.
have many user-accessible controls, such as selection between multiple
inputs, selection of desired audio and video formats, and configuration
of advanced audio processing options. To enable control of these complex
features in a user-friendly manner, an on-screen display (OSD)
is employed. OSD was usually implemented via a dedicated device, but
now HDMI transceivers offer integrated OSD engines to blend the desired
on-screen display material onto the output videooffering HTiB
manufacturers considerable savings over the external solution. Savings
of component cost and bill of materials are possible, as well as reduction
of design effort to integrate the OSD software into the system firmware.
Electronics Control (CEC) Expansion
consumer electronics control (CEC) channel is a single-wire communication
interface that facilitates home entertainment system networking. One
example is a single remote control button that simultaneously powers
all components of an entertainment system on and off. As the HDMI
standard has expanded to support new optional features such as ARC
and HDMI Ethernet channel (HEC), the CEC command library within HDMI
transceivers has also expanded to support them. For HTiB designers,
supporting the latest HDMI features requires that they also support
the latest CEC features. HDMI transceivers now handle the discovery,
negotiation, initiation, and termination of ARC and HEC sessions over
the single-wire network.
Insertion and Extraction
use of an HDMI transceiver within an HTiB is to extract the HDMI audio
for processing with a digital signal processing (DSP) chip.
The audio can then be reinserted into the HDMI stream to the TV. Since
many TVs cannot handle multichannel audio formats, the DSP chip can
downsample the audio to stereo and then reinsert the audio into the
HDMI link to the TV.
the incoming audio could be completely replaced with a new stream
from another HTiB source and embedded into the HDMI signal to the
TV. In this case, only the audio insertion feature would be used.
An example of this application could be docking an iPod® to an HTiB
and mixing the audio with an independent video stream.
HTiB system may act as an HDMI repeater when it accepts an HDMI input
and also sends it as an output, in a home theater configuration. A
Blu-ray player, for example, can be the source as an input to the
HTiB system. In order to utilize the superior sound quality of the
HTiB as compared to the connected TV, the audio must be extracted
from the HDMI signal within the HTiB. In the best case, an audiophile
would want a full 8-channel I2S audio signal output from
the HTiB, but 2-channel I2S or S/PDIF is also available
from the HDMI link. The video continues to the TV or display to complete
the system path. Only an HDMI/HDCP (High-bandwidth Digital Content
Protection) repeater or transceiver-type device can handle this
of the biggest challenges in HTiB and sound-bar design is implementing
the HDCP repeater function. The repeater function implemented in an
HTiB is a complex mix of content protection, EDID management, and
video- and audio muting. HDMI transceivers integrate the entire repeater
process into a single device and firmware, reducing system development
video and audio processing devices increase in complexity, the availability
of qualified hardware-abstracted software libraries and application
programming interfaces (APIs) becomes a major benefit to the designershortening
time to market and making it feasible to start from a well-structured
HDMI- and HDCP-compliant platform. Further savings can be made by
initially adopting the shared code base of a silicon vendor: the rewards
of integrating the code for a transceiver in low- to mid-end HTiBs
can be reaped in the upgrade possibilities when using discrete receivers
and transmitters from the same vendor in mid- to high-end HTiBs.
Circuit-Board Design for Cost Savings
HDMI transceivers offer an efficient board layout and routing scheme
by using quad flat-pack (QFP) packaging. The low-profile
LQFP package eases manufacturing cost and complexityand simplifies
inspection following manufacturecompared to more complex ball
grid array (BGA) packages. The LQFP simplifies layout challenges
to such an extent that the package can actually be laid out on a 2-layer
board, realizing a lower cost, while still achieving all the required
HDMI physical-layer compliance-test impedance measurements.
challenges on the 2-layer board include managing power supply routing
to the transceiver with sufficient decoupling, providing optimal thermal
conduction, and routing the trace impedances required for the transition
minimized differential signaling (TMDS) differential-pair inputs
and outputs. However, successful layouts that do not sacrifice performance
are eminently achievable by using surface-mount discrete devices,
employing good layout principles, and working closely with printed-circuit-board
(PCB) and silicon vendors.
transceivers offer the system designer a lower cost, lower complexity
home theater system with the latest HDMI features that consumers desire
to support their audio-visual experience. Using these transceivers,
HDMI features, such as ARC and 3D video, can now be realized. The
integrated on-screen display engine in the HDMI signal path reduces
the cost and complexity of HTiB and sound-bar designs. The ability
to extract, process, and insert audio within the HDMI stream enhances
the home theater experience in consumer system designs. Where HTiB
and sound-bar systems may function as HDMI repeaters, new transceiver
designs and firmware make the implementation seamless. Routing an
HDMI transceiver on a 2-layer board can be achieved to reduce BOM
4 illustrates a typical HDMI transceiver system using the ADV7623
from Analog Devices. It integrates a four-input HDMI receiver
(Rx) and an HDMI transmitter (Tx) with audio extraction. After
the HDMI signal is decoded, the audio content is extracted and processed
audio DSP. The processed audio can then be sent to amplifiers and
speakers, or can be reinserted into the HDMI signal path. This particular
transceiver also has integrated OSD, making it practical for sound-bar
system design, as it can save the costs of using a discrete OSD engine.
The ADV7623 provides EDID replication, HDCP repeater support, and
ARCand supports mandatory 3D video formats. Available now, the
ADV7623 comes in a 144-lead LQFP package that facilitates 2-layer
4. HTiB system using the ADV7623 HDMI transceiver.
transceivers integrate a multi-input HDMI receiver and HDMI transmitter
in a single chipwith flexible audio extraction and insertion.
Utilizing HDMI transceivers for HDMI A/V repeater designsincluding
AVRs, HTiBs, and sound barswill:
the system bill-of-materials costwith fewer components, smaller
PCB area, and fewer PCB layers.
reduce both the hardware and HDMI repeater system software design
efforts, thus greatly reducing the time to market.
advantages make HDMI transceivers an excellent choice for cost-effective
high-performance home audio/video system design.
the HDMI logo, and High-Definition Multimedia Interface are trademarks
or registered trademarks of HDMI Licensing LLC in the United States
and other countries.
a staff engineer for the Digital Video Processing Group at Analog
Devices (Greensboro, NC), is a team leader for HDMI and other video
interface products. With over 15 years' experience in the semiconductor
industry, he has worked for ADI since 1999. He holds a bachelor's
degree in electrical engineering from North Carolina State University
and an MBA from the University of North Carolina at Greensboro.
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a senior applications engineer for the Digital Video Processing Group
at Analog Devices (Limerick, Ireland), has worked for the company
since 2007. He works on HDMI receiver, transmitter, and transceiver
products. He earned his primary BEng degree from University College
of Cork in 2002 before continuing to complete his MEng through research
at the University of Limerick in 2004.
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is a product marketing manager for the Digital Video Products Group
at Analog Devices. He has been with ADI since 2003 and specializes
in video and display products. Lie has a BS from Fudan University,
China, and a PhD in physics from Wayne State University.
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