(Editor's Note: this article contains many phrases and acronyms unique to consumer and multimedia design. If you are doing any work in this area, you should become familiar and comfortable with them! There is a list of all the acronyms used, below the “About the authors” section at the end; if you are ambitious, see how many you can spell out and properly explain.)
Now that large screen HDTVs (High Definition Televisions) have achieved widespread acceptance, many consumers are expanding their electronics collection to include components which complete a home theater system. Home Theater in a Box (HTiB), sound bars, and A/V receivers (AVRs) are home theater systems which enhance the user experience with superb audio, while complementing the HDTV video performance. Being capable of extracting and processing high-fidelity audio is a key differentiator among the hardware choices on the market today. Home theater systems can now offer all the latest features of HDMI® (High Definition Multimedia Interface) seamlessly integrated within this equipment.
The 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 features while costing less and having more user-friendly controls.
Designers of home theater equipment are tasked with integrating all these new HDMI features while shrinking their BOM costs, their development costs and their time to market. HDMI transceivers are a new product category which incorporates all these technical requirements to help designers meet these challenges.
HDMI transceivers, Figure 1 , provide integration of a 4:1 HDMI input mux, HDMI receiver, On Screen Display (OSD) engine and HDMI transmitter blocks. Alternatively, these functions would each be discrete IC devices with their own unique firmware. A transceiver can provide these functions with only a single firmware solution. This also reduces board area, firmware complexity and BOM (bill of materials) costs for the home theater system designer.
Figure 1: Functional Block Diagram of HDMI Transceiver
HTiBs are complete home-movie playback systems. They generally contain a multi-channel audio amplifier and include a surround-sound speaker system for playback of audio. It has become popular for HTiBs to also include integrated video players (DVD or Blu-ray). The advantages HTiBs provide are their ease of installation and power matching between the video player, amplifier and speakers. Most HTiBs primarily process audio and only pass-through video to the TV over the HDMI interface. Figure 2 is a block diagram of a typical HTiB system.
Figure 2: Block Diagram of a Typical HTiB
Another emerging AV system with the growth of thin, large screen flat panel TVs is the sound bar. It is a speaker system that has the advantages of compact size, easy set-up and provides much better sound quality than the speakers of the TV. Since most HTiBs and sound bars are used with large screen HDTVs, their audio and video connectors mainly utilize HDMI. A sound bar will typically have multiple HDMI inputs for various sources, a single output for the connected TV and built-in audio processing and speakers. Figure 3 is a block diagram of a typical sound bar system.
Figure 3: Block Diagram of a Typical Soundbar with HDMI Hub
Advanced sound bars are composed of multiple speakers and amplifiers with surround sound decoding capability. These advanced and unique acoustic designs give a certain level of surround sound effect without putting speakers at “rear” locations in a room. Middle- to high-end sound bar solutions often have integrated DVD or Blu-ray DVD players, so their system architecture is similar to that of an HTiB.
ARC (Audio Return Channel)
A new feature in the HDMI specification allows for an Audio Return Channel. The ARC feature allows the HDMI cable to “return” 2-channel S/PDIF or multichannel audio back to the HTiB from the TV. In order to listen to the TV audio on most HTiBs, an independent cable (optical S/PDIF or coaxial) would be required to send the audio from the TV or tuner source back to the HTiB. ARC eliminates the need for this extra audio cable. HDMI transceivers offer an ARC receiver on the HDMI output port. This allows the HTiB to be able to process audio from the downstream device.
ARC adds significant value in the case where the downstream HDMI sink device, such as a TV or set top box, uses a tuner to receive new media content. Instead of outputting the audio to the less powerful internal TV speakers, the consumer can easily use the higher fidelity HTiB system output. The returned audio data can now pass on the HDMI cable from the TV to the HTiB via control signals. This is in the opposite direction of the traditional video data path over an HDMI cable. The audio can be returned over ARC whether or not there is active HDMI video out of the HTiB on the cable.
HDMI transceivers provide an EDID replication feature that replicates a single location memory across multiple HDMI ports (even when the HTiB is in power down mode). This allows for faster system start-up times since all of the upstream HDMI source devices can configure their video outputs properly before the HTiB is powered up. EDID replication is supported through the use of only the +5V/55mA available from the source via the HDMI cable.
HDMI Transceivers which incorporate HDMI v1.4a technology can pass 3D video as part of the home theatre experience. New features that significantly enhance the user experience are critical to driving TV sales. The standardization of the transmission of 3D video in the HDMI standard is such a breakthrough. This specification defines an infrastructure for communicating 3D video in the home through a list of mandatory and optional video formats.
As a bridge between 3D content providing sources (e.g. game consoles, Blu-ray players) and 3D capable TVs, HTiB manufacturers must stay ahead of the technology curve to enable customer benefit in the long term from the full range of features offered by their source and sink devices. In a practical application, the HTiB must present the connected sources a list of supported 3D formats – retrieved from the connected TV and parsed against its own list of supported 3D formats. The connected source then indicates to the HTiB when it is sending 3D content through HDMI protocol commands. The HTiB can then extract and output any advanced audio formats (which the TV may not be equipped to support e.g. Dolby TrueHD ® or DTS-HD Master Audio ®) sent over the HDMI link .
OSD (On Screen Display)
Usually implemented in a dedicated OSD device, HDMI transceivers offer integrated OSD engines to blend the desired OSD onto the output video. This offers HTiB manufacturers considerable savings from using an external solution. HTiBs have many user accessible controls – selection between multiple inputs; selection of desired audio and video formats; 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. Component cost and bill of materials savings are possible as well as minimal design effort to integrate the OSD software into the system firmware.
CEC expansion for HDMI
The CEC (Consumer Electronic Control) channel is a single wire communication interface which facilitates home entertainment system networking. An example would be a single remote control button that simultaneously powers on and off all components of an entertainment system. With the expansion of the HDMI standard to support new optional features such as Audio Return Channel (ARC) and HDMI Ethernet Channel (HEC), the CEC command library within HDMI transceivers has also been expanded to support these new features. For HTiB designers, the requirement to support the latest HDMI features drives their requirement to support the latest CEC features – the discovery, negotiation, initiation and termination of ARC and HEC sessions are now handled over the single wire network on HDMI transceivers.
Audio insertion and extraction
Another use of an HDMI transceiver within an HTiB is to extract the HDMI audio and process it with a Digital Signal Processing (DSP) chip. The audio can then be re-inserted back into the HDMI stream to the TV. Since many TVs cannot handle multi-channel audio formats, the DSP chip can down-sample the audio to stereo and then re-insert the audio into the HDMI link for the TV.
Conversely, the incoming audio could be completely replaced with a new stream from another HTiB source that can be 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.
An 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 which is then input to the HTiB system. In order to utilize the superior sound quality of the HTiB 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 eight channel I2S audio signal output from the HTiB, but two channel I2S or SPDIF is also available from the HDMI link. The video then needs to continue to the TV or display to complete the system. Only an HDMI/HDCP repeater or transceiver type device can handle this audio extraction.
One 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 control, EDID management and video and audio muting control. HDMI transceivers integrate all of this repeater process control into a single device and firmware which reduces complexity of the system development.
As video and audio processing devices increase in complexity, the availability of qualified, hardware abstracted software libraries and APIs becomes a major benefit to the designer. The benefit is not just in terms of shortening time to market but also in terms of starting from a well structured, HDMI and HDCP compliant platform. Further savings can be made by 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 when it comes to using discrete receivers and transmitters from the same vendor in mid to high end HTIBs.
Two-layer PCB design for cost savings
New HDMI transceivers offer an efficient two-layer board layout and routing scheme by using QFP packaging. An LQFP package eases manufacturing cost, complexity and simplifies inspection following manufacture compared to a more complex ball grid array (BGA) packages. The LQFP also simplifies layout challenges to such an extent that the package can actually be laid out on just a two-layer board, realizing a lower cost, while still achieving all the required HDMI physical layer compliance test impedance measurements.
Design challenges on the two-layer board include managing power supply routing to the part with sufficient decoupling, providing optimal thermal conduction and routing the differential trace impedances required for the TMDS differential pair inputs and outputs. However, using surface mount discrete devices, good layout principles and by working closely with PCB and silicon vendors, a two-layer PCB layout is eminently achievable without sacrificing performance.
HDMI features such as ARC and 3D video and can now be realized with new HDMI transceiver products. Integrated OSD 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. While HTiB and sound bar systems may function as an HDMI repeater, new transceiver designs and firmware make the implementation seamless. Routing an HDMI transceiver on a 2-layer board can be achieved to reduce BOM costs. HDMI transceivers offer the system designer a lower cost and lower complexity home theater system with the latest HDMI features that consumers will want to support their audio visual experience.
Figure 4 is a typical HDMI transceiver system block diagram using the ADV7623 offered by Analog Devices. It integrates a 4-input HDMI Rx and an HDMI Tx with audio extraction.
Figure 4: HTiB System Design using ADV7623 HDMI Transceiver
After the HDMI signal is decoded, the audio content is extracted and processed by an audio DSP. The processed audio can then be sent to amplifiers and speakers and can be inserted back to the HDMI signal path. This particular transceiver also has integrated OSD which is practical for sound bar system design since it can save the cost of using a discrete OSD. The ADV7623 provides EDID replication, HDCP repeater support, ARC, and supports mandatory 3D video formats. The ADV7623 is available now and comes in a 144-LQFP package which supports two-layer PCB design.
HDMI transceivers integrate a multi-input HDMI receiver and HDMI transmitter in a single chip with flexible audio extraction and insertion. Utilizing HDMI transceivers for HDMI AV repeater designs including AVRs, HTiBs, and sound bars will:
(1) Save the system BOM cost with less components, smaller PCB area, and fewer PCB layers
(2) Greatly reduce the hardware design effort as well as the HDMI repeater system software work thus greatly reduce the time to market
These advantages make the HDMI transceivers an excellent choice for cost effective designs of high-performance home AV systems.
About the authors
Lie Dou is a Product Marketing Manager for Digital Video Products group at Analog Devices. He has been with ADI since 2003 and specializes in video and display products. Lie has a B.S. from Fudan University, China and Ph.D. in Physics from Wayne State University. He can be reached at .
Joe Triggs is a senior engineer with the Digital Video Products group at Analog Devices, Inc. He has been with ADI since 2007 and specializes in transceiver and video signal processing products. He has a BE from University College Cork and a MEng from the University of Limerick. He can be reached at .
Ian Beavers is a staff engineer with the Digital Video Products group at Analog Devices, Inc. He has been with ADI since 1999 and specializes in video and display products. He has a BSEE from North Carolina State University at Raleigh and an MBA from the University of North Carolina at Greensboro. He can be reached at .
Bonus: Multimedia acronyms in this article—test yourself: