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March 15, 2015


Electronics & Systems
Mobile Devices
The Basics
Nadim Maluf

You are shopping for a new smartphone and you are trying to understand how long the battery will last. But you can’t seem to get a straight answer. Apple says the iPhone 6 will last up to 14 hours of talk time on 3G but you are really not going to have your iPhone glued to your ear for 14 hours. Motorola is more subtle about its claims: up to 24 hours of mixed use. Other manufacturers follow the same strategy of being vague about their claims with the operative word being “up to.”  

The reason nobody wants to commit to battery life is you, the user and consumer. We each use our mobile device differently. Some of us use the device as a phone more frequently, others use apps more intensively. Some of us turn off plenty of background services such as data refresh, whereas others want their GPS operating with as many apps that request it. This creates an infinite number of combinations of use, and hence makes the “average user” profile somewhat of an oxymoron. This blog will shed some insight onto what components and features in your mobile device are power hungry and what you can do to limit the times that these power-hungry features are allowed to access your limited battery capacity.

The most power intensive components in a smartphone are the display, the processor (or CPU), the various radio functions (and there are several radios in your smartphones), the location services, in particular the GPS system, and the memory, in particular, writing into memory. Naturally, they are not equal in their power consumption, so we will attempt to put some power figures for each of them as well as rank them in terms of their power needs.

1. Displays: The display and its associated electronics (backlight, touch screen controller, graphics processor) are by far the most power hungry component in your mobile device. Modern smartphones have some pretty impressive displays but the more pixels they pack, the more power they consume. The Galaxy S6 has a spectacular 2560 x 1440-pixel Quad HD display but I can imagine it will be a serious power hog. Naturally, Samsung will not share these power figures with the public but one can estimate from various publications and lab tests these power levels to be about 1,000 mW for a standard 5-in HD display, and rising to 1,500 mW for the quad HD screens. A battery with a capacity of 2,600 mAh or equivalently 10,000 mWh, this translates to about 6 – 8 hours of active screen time. A couple of years back, these power levels were nearly half what they are now because the screens were smaller and were at most 720p. Tidbit #1: If you must have a large screen, reduce the backlight screen intensity. Backlights can consume several hundred milliwatts.

2. Processor: A an octa-core running at 2.4 GHz all the time will most likely cause a thermal shutdown of the smartphone quite rapidly. A processor running at full steam will consume 3,000 mW at its peak — and generate a lot of heat. Fortunately, these peak events are short-lived and may be infrequent depending on your usage. But still, applications that are processor intensive will invoke that processor horsepower more often than you desire and deplete your battery. Rogue applications are clearly detrimental to battery life. On average,  iOS is more power-conscious and tries to reduce the demand on the processor. The new Android 5.1 Lollipop has gotten much smarter in this segment than its predecessors, but can still benefit from more improvement.  Tidbit #2: While the OS should in principle terminate applications not in use, keep an eye on rogue apps that continue to run in the background or when you don’t need them. Shut them down or better yet, remove them from your device.

3. Networking and radios: Your smartphone contains several radio systems. A modern device will have a LTE radio and a separate 3G radio, and possibly an older 2G radio. It will have a separate WiFi radio and a bluetooth radio, albeit these two are usually low-power, relatively speaking. These radios have power amplifiers for their transmit-receive functions. These power amplifier consume a lot of power — to amplify the signal — when the network signal (the number of bars on the top of your screen) is really low. In other words, if your signal level is low, the smartphone will compensate for that by boosting its own transmission power, hence more power consumption. How much power: what is an average power of 1,000 – 1,500 mW could double or more. Tidbit #3: Turn off unnecessary radios (WiFi, bluetooth or LTE radio if there is no LTE signal). Turn off background data refresh and do not let apps have unfettered access to the network radio (especially 3G and LTE) in the background.

4. Location services: The location services utilize an integrated chip that includes a GPS transceiver complemented by another integrated chip with accelerometers and gyroscopes. A GPS chip will consume approximately 25 mW and the accelerometer/gyroscope will consume another 25 mW — that’s 50 mW in total. It surely is far less than the radio and screen, but in a world of limited power budgets, every mW counts. Tidbit #4: More and more apps are requesting to access locations which turns on these services and consumes power. If you don’t need them, turn these background location services off, and limit them to only the apps that are essential, such as navigation. Also, terminate the apps that use location services if you are not using them. Google Maps and other map apps are apps that like to check your location frequently. Terminate it if you are not using it.

5. Data storage: For most users, we don’t write into memory very frequently. Memory includes the flash memory in your device (those 32 or 64 GB that hold your files and music and photos), as well as the SD Card that boots your storage by a large amount. But if you are a user who loves to use the camera feature continuously, more importantly the video, then you may be in for a surprise. Each MB file consumes a peak of 400 mW of power to be written into memory. Uncompressed standard HD (1080p) video file is 3 MB per second. Assuming an optimistic 10:1 file reduction after compression, that translates to 120 mW for each second of recording. The newer 4K video format has a whopping uncompressed bitrate of 40 MB/sec. That will be a serious power hog! Tidbit #5: If you want to record video on your smartphone, reduce the resolution to the minimum you are willing to live with. You will be surprised to see how great the 720p quality looks on the screen.

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