Military Embedded Systems

The future of power management in the mobile computing market

Story

October 28, 2013

Charles Limonard

Dialog Semiconductor

2013 is proving to be a milestone year for the mobile computing market, with a wider choice of entry-level and high-end smartphones becoming available and tablet sizes and prices shrinking, spurring record sales on a global basis. At the same time, power management is fast becoming the defining issue of the era, as consumers want to be able to consume more multimedia content on the move for longer between battery charges.

More smartphones are forecast to be shipped globally than feature phones for the first time in our industry in 2013. International Data Corporation (IDC) predicts some 918.6 million smartphones will be shipped to vendors, representing 50.1 percent of the total worldwide mobile phone market. We’re seeing smartphone prices fall globally, a greater choice of entry-level to high-end models on the market, and an acceleration of 4G LTE network roll-outs, making these “do-it-all” devices an increasingly attractive option for consumers. China supplanted the U.S. last year as the global leader in smartphone shipments, but we are also seeing burgeoning demand in Brazil and India with their large, populous nations, high-growth economies, and rising middle classes.

The prospects for tablets are similarly positive. Tablets are likely to out-ship notebooks in the U.S. for the first time this year. The buying public can't get enough of the devices, and this is expected to persist in the longer term on a global basis. IDC has recently raised its tablet shipments forecast for the 2013–2016 period, suggesting global tablet sales will reach 190.9 million in 2013. By the end of 2017, IDC expects tablet vendors to have shipped in excess of 350 million units with a rapidly growing choice of smaller, cheaper slates. We’re seeing a confluence of high-end tablets and ultra-mobile notebooks as the world figures out how these devices can co-exist and hybridize.

Effective power management presents an increasingly complex array of design challenges for these portable devices. Poor battery life contributes to customer dissatisfaction with a new smartphone more than any other single feature. This will only become more of an issue over time unless vendors take new innovative approaches to their power management strategy.

4G smartphones use substantial battery life searching for next-generation network signals, which are currently scarcer than 3G signals, and they eat up more battery power decoding high levels of data that can be transmitted within the spectrum. In addition, consumers are now using their mobile devices more extensively – they talk, text, email, and surf the web, but they also want to be able to view higher-definition videos and GPS maps, conduct two-way video calls, play more immersive games, and stream music. At the same time consumers demand displays that are brighter, bigger, and incorporate better touch functionality, and, in the future, haptic feedback. Each of these features is a major battery drain, creating a need for effective power management technologies.

Power management remains a critical challenge

In the past, power management technologies used to be integrated within the application processor. However, as the importance of optimizing power performance becomes more important and technically challenging, this on-chip approach is no longer possible. Dialog’s companion Power Management Integrated Circuits (PMICs) are highly programmable, enabling them to support the voltage scaling and power delivery sequencing required by single or multicore application processors, as well as all the sub-systems in the phone, such as the network and connectivity stack (3G, 4G LTE, Wi-Fi, Bluetooth, and NFC), the display, high megapixel cameras, and more.

 

Figure 1: The functionality expected in modern mobile devices demands increasingly complex power management capabilities.

(Click graphic to zoom by 1.6x)


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There are good reasons for having a companion PMIC that is highly integrated with all the key communications, multimedia, and processing blocks on the board of a mobile device. The PMIC has to generate up to 30 different power supplies to be able to feed different parts of the applications and baseband processor with the right combination of voltage and current. If designers take an on-chip approach to power management, with the application processor handling these tasks, they need a high-current supply that can only be carried by aggregating many pins. System-on-Chip (SoC) designers can avoid the additional die and efficiency cost of on-chip power management by using individual low-voltage, low-current supply rails that are supplied off-chip by the dedicated, companion PMIC.

A diversity of power management needs

The market for smartphones is diversifying as they are adopted on a global basis. A platform approach is becoming increasingly more important in smartphones as vendors seek to give consumers more choice of models, spanning the high-end to entry-level markets with optional 4G or NFC connectivity, depending on the market. They are under pressure to launch new models every six to nine months in response to consumer demand for “the latest and greatest features” and competitor activity; a platform strategy helps them manage this process while containing costs.

A new wave of smartphone handset vendors are coming onto the market working with SoC vendors who provide a complete reference platform to OEMs to help reduce time to market and development risks. Of course, it’s important that OEMs have the capacity to customize a platform to differentiate the products they are developing on the market.

PMICs enable vendors to be flexible in designing their smartphone platforms and launch multiple models and designs for different markets and over the “life cycle” of that product. They support late changes in board-level designs as additional functionality that is added into smartphone platforms during the R&D process. This can also help to reduce PMIC inventories and respond to the consumer market’s need for volume flexibility. This customizability is also a huge advantage to new handset vendors working with SoC vendors.

The move to multicore devices

The vast majority of smartphones today are single- and dual-core SoCs. At the very high end, there is a smattering of quad-cores. The same is mostly true of tablets, although the larger power budget (up to 4 W for a passively cooled device and as high as 7-8 W for systems with fans in comparison to around 1 W for smartphones) means that the processors tend to skew toward higher core counts.

Some have questioned the need for multicore mobile computing devices. It’s certainly true that the majority of PCs sold today have dual-core CPUs, as most software applications are single-threaded rather than multi-threaded and are able to work off a number of cores. Software for mobile devices is even less amenable to threading.

Despite this, there is a significant power advantage to be had from multicore devices. Multicore devices delegate simple tasks to one core, while directing more complex, power-hungry tasks to the other core. Each of the quad- or octal-core application processors needs to be powered up and down into and out of sleep state in particular sequences. The PMIC acts as a conductor for the system, telling individual blocks inside each baseband or applications processor device when to wake up and when to go to sleep to save energy. Most workloads will still be single-threaded and need high frequencies, so the SoC must be able to efficiently deliver both aggregate throughput and single-core performance.

Heterogeneous cores, which ARM bills as “big.LITTLE,” pair a small and efficient core with a larger and more complex core and switches between the two. The challenge again is power and reducing switching penalties through an effective power management solution. Put simply, there isn’t enough power or cooling for every block to be in a high-performance mode simultaneously. When running a highly immersive and interactive game, the display and GPU will draw much of the power; the CPU will actually have to reduce frequency and voltage to deliver the best overall performance. This becomes even more complex if there is significant wireless traffic as well. As a result, an advanced PMIC is required to handle these switching processes (Figure 2).

 

Figure 2: Power management is migrating from the application processor into a dedicated external PMIC, like this DA9063 from Dialog Semiconductor.

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4G LTE and the power performance challenge

4G LTE smartphones also present a power performance challenge. Today’s digital modulation techniques compress more data bits into every RF channel, resulting in more complex waveforms with higher “crest factors,” expressed as Peak-to-Average Power Ratio (PAPR).

LTE signals have a very high crest factor (typically, 7.5 to 8 dB PAPR), resulting in a much higher peak power requirement for the transmitter. Traditional fixed-supply PAs are only energy efficient when they are in compression, at the peaks of the transmitted waveform. If designers opt to use a larger Power Amplifier (PA) with an increased supply voltage, a lot of energy is wasted and the time consumers are able to use LTE devices between battery charges can drop to a matter of hours. To optimize power performance, two companion PMICs are required to manage the more complex voltage and current requirements of the smartphone.

Saving board space

OEMs are also under pressure to save board space, freeing up “real estate” for new functionality and helping them keep their devices thin while reducing costs. The use of 3D packing technology – or chip stacking – is paying dividends here. Typically, chip stacking relies on connecting different layers of the stack with low-density bond wires or solder bumps. Combining a fully configurable PMIC with a low power audio codec that is monolithically integrated, or stacked, in a single package delivers significant board space and cost savings. This can involve the integration of over 30 different high- and low-voltage circuits and analog functions on a single chip.

Manufacturing trends

We’re also seeing the relentless drive toward thinner and smaller geometry devices that pack in more features than ever before. Ever-finer feature sizes potentially introduce the perils of high leakage current due to short-channel effects and varying dopant levels, which ultimately threaten to derail the industry’s progress to smaller geometries.

We’ve also seen the advent of novel stack materials, such as high-k/metal gates, and now fully depleted transistors, for example, FinFETs. Modern FinFETs are 3D structures that rise above the planar substrate, giving them more volume than a planar gate for the same planar area. Given the excellent control of the conducting channel by the gate, which “wraps” around the channel, very little current is allowed to leak through the body when the device is in the off state. This allows the use of lower threshold voltages, which results in optimal switching speeds and power.

There is plenty of other promising research for the roadmap. Dialog, for example, is working with Taiwan Semiconductor Manufacturing Co. (TSMC), the world’s largest contract chipmaker, on state-of-the-art 0.13 micron bipolar-CMOS-DMOS (BCD) technology to integrate advanced logic, analog, and higher voltage components into a smaller form factor, single-chip power management IC to support next generation smartphones, tablets, and Ultrabooks.

The BCD process technology epitomizes the relentless innovation that drives the semiconductor industry – on the application, design, and process technology fronts. The technology incorporates analog Bipolar (B) components, Complementary Metal Oxide Semiconductors (CMOS) and high-voltage transistors Double Diffused Metal Oxide Semiconductors (DMOS) on the same die. System designers are embracing this technology since it reduces power losses, board space and costs. Silicon partners like Dialog are championing BCD as it helps build better, smaller, and more innovative products. While the foundries also have a key role to play as BCD technology is manufactured on 200 mm wafers, allowing them to extend the usefulness of their almost fully depreciated lines and either reduce the cost for end-customers, preserve margins, or free up investment for other emerging technologies.

Making smart future bets

Dialog also continually has an eye on the future, trying to identify the emerging technologies that will continue to transform the industry. For example, we have recently partnered with Arctic Sand Technologies, Inc., an MIT spin-off that is commercializing an innovative new approach to power conversion for multiple markets, including smartphones, tablets, Ultrabooks, and data centers.

DC-to-DC power converters are the underlying building block of today’s power management Integrated Circuits (ICs). Arctic Sand’s patented Transformative Integrated Power Solutions (TIPS) technology uses a unique approach for conversion, based on switch capacitive techniques.

The technology facilitates the use of smaller inductive components, resulting in increased efficiency and an overall higher power density factor over and above today’s competing technologies, delivering significant advantages in portable and data centre applications.

Harnessing the growth of mobile computing

Demand for mobile computing devices is only going to increase according to industry forecasts. Mobiles are evolving from personal information devices to mobile computing platforms that are critical to our everyday needs. Power performance is fast emerging as the defining issue of the era. Smartphone owners who are highly satisfied with their device's battery life are more likely to repurchase the same brand of smartphone, compared with owners who are less satisfied.

Consumers want a greater variety of devices in our lives. For example, a minority of consumers actually buy a 3G or 4G data plan with their tablets, preferring to use Wi-Fi in their homes and business to access and consume media. What is clear, however, is that people want to live in an untethered, wireless way. This places added pressures on battery life of portable devices, requiring a relentless focus on power management innovation across the triple play of smartphones, tablets, and the new hybrid tablet/notebooks coming onto the market.

Charles Limonard, product marketing manager for the mobile business group at Dialog Semiconductor, has over 18 years of experience in the global electronics industry and strong technical know-how. Prior to joining Dialog he held senior roles at NXP Semiconductors and Philips Semiconductors. He holds a BSc in Electronics from Hogeschool van Utrecht in the Netherlands.

 

 

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