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    Cary Chin is Director of Technical Marketing at Synopsys. His background at Synopsys is in R&D where he has managed the Power Compiler, Primepower, PrimeTime PX, and DC-FPGA products.

    Cary is a member of the Solutions Marketing Group, and focuses on the Synopsys Eclypse Low Power Solution.

iPhone 4S Power Efficiency Improvements

Posted by Cary Chin on January 27th, 2012

This blog originally posted on the Low Power Engineering Community 11/3/11.

I’ve had my iPhone 4S for a few weeks now, and have gotten to know it pretty well. Mine is the 64GB model, mostly because I want to play around with the new 1080p video recording capabilities, and don’t want to worry about running out of storage space all the time.

I’ve read many reports online about runaway battery consumption with the new 4S, but I haven’t noticed any huge change vs. my iPhone 4 in battery behavior. I still charge it every night and most of the time when I’m at my desk in my office.

From a hardware perspective, the iPhone 4S pretty much delivers as expected. The dual-core A5 processor zips along with plenty of headroom, smoothing out many of the rough spots in everyday usage that have started to creep in since the iOS 4.3 update. The camera upgrade boosts both still image and video (1080p) performance into the realm of most modern point-and-shoot cameras, although the lack of any optical zoom is still a big limitation. On the other hand, the wide availability of camera and photo enhancement apps pretty much make up for the lack of optical zoom. Battery capacity has increased minimally, but not enough to make any practical difference.

From the power efficiency standpoint, by far the most interesting new hardware feature is the new dual-antenna design, which eliminates the infamous “death grip” effect of the iPhone 4 and improves cellular reception in general. Combined with the new communications chip that boosts data rates (for GSM networks), the new radio setup is worth looking at—especially since we’ve seen that the radio can contribute even more to the energy equation than the display.

The runaway star on the software side with the iPhone 4S and iOS 5.0 is Siri. Reminiscent of a cross between HaL and the famous Star Trek “Computer,” Siri listens, seems to think, and generally does a better-than-expected job of carrying out your wishes. While still clearly early in the development cycle, Siri feels to me like the beginning of a paradigm shift where we may actually become just a productive without a keyboard as with one. I’ve dictated quite a few e-mail and text messages with Siri (sometimes while driving!), and accuracy is very good—or very bad. That to me is an indication of evolving and improving AI on the recognition side. And as is usual for Apple, the real genius of the Siri interface is the simplest part of it: You simply hold your phone up to your head to start talking to Siri. To everyone else, it just looks like you’re answering a phone call! I wish I thought of that…

Running the 4S though my usual battery (pun intended) of power tests running the Star Trek movie resulted in the following:

The results were surprising in several respects. First, the 4S seemed to be extremely efficient in the “Max Battery” mode. It played through the entire movie consuming just 0.6 Wh of energy. That would be more than 18 hours of continuous movie playing, although you can’t see much at the lowest brightness setting. This is almost a 40% improvement in energy efficiency vs. the iPhone 4! The new lower power A5 chip is likely at the heart of this result. These days video decoding is an almost-routine task, and can probably easily be handled on one of its cores.

Turning the display to full brightness (the “Max Brightness” test) shows the expected result. The energy cost of running the display at full brightness is about 0.6 Wh for the two-hour movie. The display on the 4S isn’t notably different than on the iPhone 4, so this is expected.

Turning up the sound to maximum (“Max Movie” mode) shows one other interesting change. On the iPhone 4, there was virtually no change in energy consumption between the runs with the sound muted or with the sound at maximum. On the iPhone 4S there is definitely a measurable difference, both in energy consumption as well as in the perceived loudness of the sound. In fact, with the sound at maximum, the tiny speakers in the 4S produced enough sound to make it annoyingly loud as I was trying to do some other work. I had to resort to my “manual” muting method (putting a piece of tape over the speaker) to conduct my tests.

Well, I’m about out of space and time for this post. Next time I’ll describe the results of testing the new iPhone 4S dual-antenna and modem chip setup. These results are very interesting.

In late breaking news, Apple just announced a software update, iOS 5.0.1, which among other things “fixes bugs affecting battery life.” No big surprise, as the complexity of today’s smartphones rivals any other computing platform—and dwarfs the others when it comes to power management. In particular, the interaction between hardware and software to minimize energy consumption is very difficult to model and predict, but the ramifications on battery life are immediate and sometimes ugly.

And by the way, if you are interested in learning more about low power hardware design, my colleague Josefina Hobbs is hosting a new series of short videos covering everything from introductory concepts to selected advanced low power design topics. Check them out here.

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2 Responses to “iPhone 4S Power Efficiency Improvements”

  1. vickymoraya says:

    nice bunch of info, well compiled, iPhone 4 just rocks! thanx!

  2. Jarhead says:

    I’ve seen a huge difference in power consumption between 3G and 4G on Verizon, what was causing it was the 4G consumed several times more power when driving.

    I’ve partially shielded it and found it consumes more power in 4G.

    Then I drove to a friend’s house outside of town where 4G is really spotty, and found my Bionic was consuming power so fast that it gets surprisingly hot and discharged it’s battery in just 2 hours. And this was with doing nothing on the phone. Putting it into 3G and leaving it there (as it was discharging really slow), two days later, the phone battery was still not discharged.

    To me, 4G seems to consume tremendously huge amounts of power when it is searching for cell sites (towers) or if the signal is poor. I often go into the mountains where there is no valid 4G or 3G signal at all, in 4G the phone gets too hot for my pocket, and depletes the battery- however if I put it in 3G, it doesn’t get warm. However while walking or driving, on occasion, text messages will get through, however sending a 178k picture will not work (maybe due to file size). Watching the bars, you’ll get a 1G white bar for a few seconds once and a while.
    (remember this if you think you can navigate by cell phone (example Google Maps) where it needs to download the map- cell phone navigation is usually useless without connectivity. The Pre-cache cap they have added to Google Maps in the latest Beta is still just 20Mb and is useless as it only covers a very small area with details enough to show even the main paved mountian roads (non-highway). This is were a dedicated Garmin really shines and is invaluable, and will even show most dirt and gravel roads.

    Most of the mapping apps that interface with Google and other services to download maps are now restricted by Google, or even prevented from downloading a single tile at a given zoom. Before this, tremendous bandwidth was being consumed from the Google servers, and it benefited Google not.