Low Power Dominates CES

By Pallab Chatterjee
The 2011 Consumer Electronics Show was dominated by tablets and other mobile devices, and the common theme was communication and data access anywhere anytime. From a design perspective, that translates into two main systems targets and one major constraint. The two targets are wireless connectivity and high performance graphics. The major constraint is power use. The power is a combination of idle state power and active power.

The wireless connectivity has expanded to multiple options, all of which now have high bandwidth. The standard connectivity has been with WiFi utilizing 802.11a,b,g or n protocols. For applications requiring video data transfer, the protocols are at least 802.11g or 802.11n. The other methods of connectivity are 3G and 4G/LTE cellular connections. These are all general-purpose connections to the Internet and they support a wide variety of data transfer models. The data may be small packets such as PDF files and e-book files, or larger streaming applications such as HD video or online gaming. These larger streaming applications require more power because the RF subsystem has to both remain on and active over the duration of data transfer. In the area of gaming and movies, this can be several hours.

Other popular wireless connectivity options include WiDi, Wireless HDMI , WHDI (wireless home digital interface), Bluetooth, Zigbee, and Z-Wave. These have similar power architectures to the other RF transceivers, which utilize active-power, standby-power, and sleep-power modes. These blocks need very-low-power control logic to handle the power mode switching, as the target use time in standby/power down is between one and four weeks. Color tablet computers are looking for five-plus day standby mode with RF off; cell phones are 10 to 14 days of standby mode with the RF on standby for calls/messages/e-mail notifications; and e-readers require four weeks of standby with the RF off and the data loaded on the device/a static display.

Power is also the driver for graphics style and performance. The easiest place to see the impact is in the e-reader market. This has two basic technologies—grayscale e-paper without backlight, and color displays with backlight. The products recommended for intense readers are the e-paper screen designs that do not consume any power once the page is loaded. Without the backlight, and without the need to refresh, these devices can go up to a month between charges. The drawbacks in this technology are the lack of color and a slower response time. As a result, these are dedicated readers and browsers of standard static web pages, not video playback devices.

The size of the screen and its resolution drives the power needs. The larger the screen, the more power for backlighting. The higher the resolution, the more power that needed for the CPU and GPU to display the image. If the system utilizes a video codec, such as H.264, the tradeoff on power becomes more complicated. Traditionally the codec has been in software for these mobile devices. However, with long-format video data and gaming and movies, keeping the CPU and GPU running for long periods of time to handle the decoding may use more power than a custom hardware implementation of the codec with its own power control. The codec allows for the GPU to be turned off, and most of the CPU to be turned off, with the streaming data going directly to the codec. A number of the tablets at this year’s CES took this solution for the media player targeted applications.

A common power constraint for all of these systems is the battery. Whereas laptops and netbooks have a significantly large form-factor to support large batteries, these new products do not. The thickness, lack of a fan for cooling and the need for recharging drives the peak battery power. In the trend for mobility, a recent surge in the use of inductive “wireless” charging for mobile devices has risen. The Wireless Power Consortium has created a standard labeled “Qi” for products that support a peak power of 5W and target 70% maximum efficiency on power conversion.