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The Thermal Efficiency Behind Smartphone Trends

In our second blog post on the power and thermal challenges that face modern devices, we will explore the current trends in the industry and the technologies and innovations that make them possible.

Our phones are getting bigger. As the capabilities of smartphones have grown, so have their screens. The increased demand for more visual real-estate on our pocketable devices is a global trend. According to ABI Research, almost 83 million phablets, or phones with a five inch screen or greater, were shipped in 2012.  That is an increase of 4,504% from 2011. The same body of ABI Research also states that shipments of such phones are expected to grow to 273 million in 2017.

Not only are these screens bigger, but they are higher resolution, which means they consume more power and require more processing horsepower. Almost every standard flagship phone today has at least a 1080p screen. Tablet resolutions are even higher, with Qualcomm Snapdragon 800 processors supporting up to 2560x2048. Armed with these larger screens and crisper resolutions, users are able to demand more from their devices. After all, watching HD video or gaming on 6” phablet is a much more immersive experience compared to the 3” pixelated phones of yesteryear.

One might expect that if mobile devices’ horsepower increased to enable these new experiences, the thickness of the device would grow as well to compensate for the added power and heat from these components. In reality, the exact opposite is true. Tablets and smartphones are getting thinner. For example, the Sony Xperia Z Ultra powered by the Snapdragon 800 processor, weighs in with a massive 6.4” display, but launched as the “world’s thinnest HD smartphone,” at only 6.5mm.

To recap: larger screens, higher resolutions, and SoCs with more horsepower, yet devices are getting thinner. How is all of this possible? The answer is great engineering.

Let’s begin with where this thermal and power efficiency is visually demonstrated. The GPU is responsible for pushing millions of pixels to your display and does so up to 60 times each second. During gameplay it is called upon to render 3D worlds in ultra-realistic detail, all while the CPU may calculate the artificial intelligence of the game characters or the physics of the explosion you just caused. All these high performance tasks could make other SoCs burn a lot of power, and generate a great deal of heat. Snapdragon SoCs have a history of being cooler than the competition.

Mobile devices have a very different set of thermal constraints. In the archaic PC segment, desktop computers are housed in large enclosures and are cooled by thick metal heat-sinks with a large and often loud fan. In contrast, mobile devices are mere millimeters thin and are expected to be held in your pocket, your hand, or against your cheek. There are certain thermal thresholds that must be met for a handheld to be a viable product. Skin temperature is one of them. If the devices’ thermal threshold is surpassed, the SoC begins to throttle back its frequencies, and thus performance, in an effort to reduce the heat. This can have negative impacts on performance and overall user experience. 

OEMs’ design decisions are able to help mitigate some of this heat. The proximity of high power components and the material used in the phone to dissipate the heat are some of the methods employed. Qualcomm Technologies, Inc. (QTI) actively works with OEMs to address their thermal needs. Before the handset is ever launched, QTI provides a thermal dashboard and model to help OEMs understand how their design decisions will impact performance and temperature. Still, metals, fancy plastics and PCB layout are not the only tools to solve this problem.

Snapdragon processors are designed to enable lower power and thermal envelopes by a suite of features. The Adreno™ GPU is the visual center of Snapdragon, rendering 3D environments and painting pixels to your display. There are two different methods to render 3D images to the screen, deferred and direct rendering. Adreno utilizes both methods and dynamically switches between the two modes depending on which will deliver the best power efficiency. Deferred rendering breaks the scene into smaller tiles and renders them independently. Rendering smaller tiles consumes less memory and allows operations to remain on the GPU memory, and so these operations are not penalized for accessing the larger, longer latency external memory.

Direct or immediate rendering does not buffer any content, but computes the scene as a whole and renders all pixels directly and immediately to the screen. While less efficient for accessing the external memory and potential overdraw, there are still some scenes or even parts of scenes that will benefit from this approach. Because it has the flexibility to decide between the two rendering methods based on the one that delivers the optimal power efficiency, this technology is called FlexRender™.

Meanwhile Krait processors, the CPU of the Snapdragon SoC, are designed with aSMP, or asynchronous symmetrical multi-processing. Each CPU core is on an independent voltage plane. This allows each core to adjust its frequency to accomplish a task. While other SoCs force all cores to run at the same max frequency for a single-threaded task, Snapdragon allows that single active core to run at the needed speed while the others remain off or at a lower frequency.

Of course, a phone is not a phone at all without a connection to the outside world, so Snapdragon optimizes its modem for power and thermal efficiency as well. There are high level reasons behind Snapdragon processors modem power efficiency. First, QTI creates and owns all of the key IP blocks of the modem, which allows for optimization at the system level. There are also performance and power improvements from one generation to the next. Second, QTI’s history of modem leadership is evidenced by the multi-generational lead over competition, and each design is more power efficient than the last. 

At the lower level, QTI has been the first to commercialize many features which enable power savings in LTE modems. 

Envelope tracking is one of the more recent QTI innovations in connectivity. This technology applies to the RF (Radio Frequency) amplifier, designed to allow the voltage to adjust to achieve peak power efficiency. The excessive power output (shown in the yellow below) is dissipated as heat. Snapdragon powered devices with this feature will reduce the thermal footprint and RF power consumptions by up to 30%. Snapdragon processors will be coupled with the industry’s first modem-assisted envelope tracking for 3G and 4G LTE devices.

Connected Mode Discontinuous Reception (CDRX) can turn off the LTE receiver when data is not being actively sent or received. This simple idea can lead to significant system power savings, up to 15% lower power for web browsing and up to 20% for YouTube streaming. (See page 6 of this recent Qualcomm Technologies presentation for more info.)

Not only is the Snapdragon SoC optimized for power consumption, but it also is designed to achieve the highest data rates. Starting with the Snapdragon 800 processor, QTI brought the first LTE-Advanced modem to the world. Coupled with Carrier Aggregation, Snapdragon processors can achieve speeds of up to double the previous generation. This massive speed boost can allow the phone to download your content quicker, preventing the modem from heating up over a longer period of time.

QTI’s power saving features extend beyond silicon and into software. Snapdragon Battery Guru is an app designed to extend your battery life and longevity by automatically adjusting your smartphones settings. Upon installation, there is a brief learning period while the app learns your usage habits. Once it’s ready, it will disable certain features or apps when it knows you’re not using them. For example, it will learn that you are connected to a Wi-Fi signal at home from 6PM to 6AM, but during the workday, you’re only connected via 4G LTE. During the day, it will shut off your Wi-Fi connection so it is not burning unnecessary power searching for a connection. Or similarly, Snapdragon Battery Guru will recognize you do not conduct Skype calls in your sleep, so it will disable the connection to the internet if it is not needed. But if you do want to receive a Skype call at 2 a.m., Snapdragon Battery Guru allows for customization and you can override for each app as you see fit. Snapdragon Battery Guru is available on the Android Google Play store for your Snapdragon powered device.

Beyond silicon, QTI even addresses thermals at the packaging level. Snapdragon processors are now housed in 4-channel PoP (package-on-package), which lowers the thermal resistance on the package by allowing for more heat transfer back into the circuit board. This technology can help keep the SoC up to 5 to 15 degrees Celsius (41 to 59 F) cooler. Lower temperature not only results in higher performance, but up to 30% lower leakage.

How does this all translate in the real world? Just take a look at the LG G2 smartphone. In a recent review by AnandTech, this flagship handset is topping the charts in CPU and GPU performance. Those high performance scores do not result in high power, as the G2 also took the top spots in their battery life tests. To quote the author, “The LG G2 battery life is shockingly good through our tests, and in subjective use.” In the talk time test, it lasted over 8 hours longer than the 2nd place contender and over 2.5x longer than the new iPhone 5s.

Not only do Snapdragon processor features allow for longer lasting battery life, but they allow for faster charging. With phones increasing in size, and battery technology improving, phones are slowly cramming more and more watt-hours or battery capacity into your device. The downside of this is that charge times also increase with battery capacity. Qualcomm® QuickCharge 2.0 improves charging by up to 75%. This more than compensates for the larger battery capacities and ensures you spend less time tethered to an outlet and more time on the go. Check out what was said about QuickCharge here.

The smartphone continues to evolve, both inside and out. These changes are opening up new worlds of usage models and capabilities that we previously wouldn’t have imagined could be housed in our pocket. With the sizeable list of engineering innovations discussed here, Snapdragon processors have paved the way for this mobile revolution. If you want the best performance and the best battery life, you want a Snapdragon processor at the heart of your device.

Our next post will explore some of the new user experiences enabled by these exciting Snapdragon features and others.

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