Design Article
Designing HDTVs with CEC to Energy Star 3.0
Doug Bartow
Analog Devices, Inc.
3/6/2009 2:00 AM EST
The revised Energy Star requirements for TVs were developed by the EPA in consideration of several key technologies driving TV design today. Since different types of display technologies such as LCD, CRT, plasma, OLED and rear-projection all serve the same fundamental purpose, the Version 3.0 testing criteria were designed to be technology-neutral. This allows consumers, when comparing several Energy Star TV sets, to be confident that they are equally energy efficient and that the meaning of the label is consistent across display technologies.
Wide color gamut and motion blur improvement are features that were considered for additional power allowance, but the EPA found that they had a minimal effect on power consumption compared to a TV's overall power budget. TVs with automatic brightness control (which have lower power consumption in low ambient light conditions) were considered in the total power calculation formula and are also noted on the Energy Star Product List.
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Table 1: PMax = maximum allowable On Mode power consumption in watts
A = viewable screen area of the product, found by multiplying the display width by the display height
Above are the Energy Star Product Criteria for TVs while operating in the power-on mode. The EPA recognizes that new display technology advances in backlights and OLED displays promise to make TVs even more power efficient. They have proposed waiting six to eight months after Tier 1 requirements (see reference table) take effect to reevaluate display technology and determine Tier 2 requirements. The EPA anticipates that future innovation in TV designs will lead to additional power savings that should be reflected in the marketplace by 2010 when the Tier 2 guidelines are scheduled to go into effect.
Next: Standby power requirements and CEC
Standby mode power level requirement for TV products
Irrespective of screen area or resolution, all TVs must consume 1 watt or less in standby mode.
A TV designer is faced with a host of design challenges in order to meet the 1 watt or less standby mode requirement. This stringent power requirement must be met without sacrificing any display performance or features that consumers highly value.
The growing popularity for the Consumer Electronics Control (CEC) function (the part of the HDMI interface standard that provides capability for "One Touch Play" control over the HDMI cable of all the electronic hardware typically found in Home Theater systems) calls for additional design consideration in order to meet the standby mode power consumption of 1 watt or less.
Standby power and CEC
CEC is a single conductor wire or bus technology that is meant to carry IR-remote and control commands between interconnected HDMI devices. It is a bi-directional link over a HDMI cable that enables consumers increased flexibility in controlling their HDTVs, Blu-Ray player, set-top-box, A/V receiver or other devices. For example, by pushing "Play" on a Blu-Ray player, CEC will send commands over the HDMI cable to power up the HDTV and A/V receiver in order to start watching a movie. CEC also allows a user to point their I/R remote at their HDTV, and press a single button (e.g.,"Play a Movie"), which will power up the HDTV, Blu-Ray player and A/V receiver.
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Figure 1: On standby, system off.
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Figure 2: Button pushed on Blu-ray player turns on all system components using CEC.
The CEC function requires that the HDTV be capable of powering up by either receiving commands from an I/R remote or from the CEC bus connection on an attached HDMI cable. The TV must be able to send or receive CEC commands while in Standby Mode. The TV designer must carefully consider this requirement in order to meet the latest Energy Star guidelines.
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Figure 3: One touch play on remote using CEC to turn on all system components
Next: Strategies for meeting standby power requirements with CEC
Meeting standby power requirements with CEC
In order to keep standby power consumption as low as possible, it is important to maintain power only to the I/R receiver and CEC controller (which are waiting to receive a power up command). When an I/R remote command is received, it is decoded and, if it is determined to be a CEC command, it gets passed over the HDMI cable to other connected devices. The CEC controller is also waiting to receive a CEC command from another connected device to power up the HDTV in response to a button push.
The CEC controller function could simply be added as another processing task implemented in the display's main microcontroller but this would result in a much higher level of power consumption. Adding a small, standalone microcontroller, dedicated to monitoring the CEC bus, would decrease power consumption, but also add cost and design complexity.
A better solution would to design in an integrated HDMI interface, such as Analog Devices' ADV7604 HDMI Receiver or ADV7510 HDMI Transmitter, both of which contain an on-chip CEC controller/buffer.
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Figure 4: Block Diagram of ADV7604 HDMI Receiver
Offering designers the flexibility of an integrated CEC controller/buffer means that CEC functionality can quickly be incorporated without a significant increase in standby mode power consumption.
Next: The CEC message buffer
The CEC message buffer
The on-chip CEC message buffer contained in the ADV7604 (and ADV7510) allows designers to utilize an existing system ASIC and still keep standby power consumption low. Instead of running the system ASIC at an elevated power level while keeping on the lookout for an incoming CEC message, it can remain "resting" in a lower power state.
A standalone CEC controller can be a more power efficient solution, as it waits for an incoming CEC message, stores it in its buffer and sends the system ASIC a system interrupt to wake it up. This powers up the system ASIC in a controlled fashion, allowing it to read the CEC message buffer whenever it is ready and decode the CEC message. Selecting an HDMI interface with an integrated CEC controller/buffer enables designers to utilize existing system hardware and software designs while quickly incorporating the popular CEC functionality.
Conclusion
The EPA has definitely "raised the bar" for TV designers by incorporating more stringent requirements for energy efficiency in its Energy Star Version 3.0 guidelines. The EPA estimates that only 25 percent of HDTVs currently entering the market will be capable of meeting these stricter requirements. The TV designer will be challenged to not only meet this demanding energy efficiency standard but will also be called on to also add exciting new features, such as CEC functionality, to their latest HDTV models. By carefully considering several design concepts, TV designers can find the optimal system solution that satisfies not only the latest Energy Star guidelines but also meets time-to-market and BOM cost goals.
About the author
Doug Bartow is the Strategic Marketing Manager for the Advanced TV Segment at Analog Devices, Inc. (ADI). Doug is responsible for defining display interface products for LCD monitors, projectors, plasma displays and HDTVs. Prior to ADI, he worked in product marketing and product development at Harris Semiconductor (now Intersil) and at Motorola. He can be reached at doug.bartow@analog.com.
