Battery life is not enough? Let's innovate PMIC design technology together!

　　With the introduction of entry-level and high-end smartphones, consumers have more choices, and tablet computers are becoming smaller and cheaper, which has stimulated global market sales records to set new records. 2013 will undoubtedly be an important milestone in the mobile computing market. At the same time, consumers want to maintain longer battery life while browsing more media content, so power management is quickly becoming a focus of this era.

　　An increasing number of forecasts indicate that in 2013, global shipments of smartphones will surpass traditional mobile phones for the first time. Market research firm IDC predicts that smartphone shipments will reach 918.6 million units, accounting for 50.1% of the global mobile phone market. Global prices for both entry-level and high-end smartphones continue to fall, giving consumers more choices, and the introduction of Long Term Evolution (LTE) network optimization makes these "universal" devices even more attractive to consumers. China replaced the United States as the country with the highest smartphone shipments in 2012, and in populous countries such as Brazil and India, fast-growing economies and a rising middle class are also driving booming demand.

　　Tablets are also expected to have a bright future. 2013 may be the first year that tablet shipments in the United States surpass notebook shipments. Consumer demand for these devices is insatiable, and it is generally expected that this situation will continue for a long time around the world. IDC recently raised its forecast for tablet shipments between 2013 and 2016, indicating that global tablet sales could reach 190.9 million units in 2013. By the end of 2017, IDC expects tablet vendors to ship more than 350 million units, with smaller and cheaper tablets also growing rapidly.

　　As portable devices become increasingly complex, effective power management solutions are a huge design challenge (Figure 1). According to the 2012 U.S. Wireless Smartphone Customer Satisfaction Study conducted by JD Powers, poor battery life causes more dissatisfaction than any other single feature for consumers of new smartphones. And this problem will only get worse over time unless vendors are willing to innovate their power management strategies.

　　Figure 1 New mobile device functional requirements are gradually increasing the complexity of power management performance.

　　4G smartphones consume a lot of battery life searching for network signals, which are now scarcer than 3G signals. They must consume more power to decode the signals transmitted in the spectrum. In addition, consumers will use their mobile devices more extensively, including chatting, sending text messages, sending emails and browsing the web, but they also want to be able to watch higher-resolution videos and satellite navigation maps, make two-way video calls with their children, play more immersive games and stream music. At the same time, consumers also need brighter, larger displays with better touch functions and, in the future, tactile response functions. Each of these features consumes a lot of power, which also creates the need for high-performance power management technology.

　　Power management remains a major challenge

　　In the past, power management technology was often integrated into the application processor. However, as power efficiency optimization has become more important and a technical challenge, this on-chip approach is no longer feasible.

　　The industry’s companion power management integrated circuits (PMICs) are highly programmable chips (Figure 2) that support the voltage scaling and power delivery sequencing functions required by single-core or multi-core application processors, as well as subsystems in phones such as the network and connectivity stack—3G, 4G LTE, Wi-Fi, Bluetooth and NFC—displays, high-pixel cameras, and more.

　　Figure 2 Power management is being separated from the application processor into a separate PMIC.

　　There are many good reasons why it is important to have a secondary PMIC that is highly integrated with all the communications, multimedia, and peripheral processing circuitry on a mobile device. This PMIC must be able to handle up to thirty different power supplies for various parts of the application processor and baseband processor, with the right combination of voltage and current. If the consumer power management is embedded on-chip, the application processor will handle these tasks, requiring a high-current capable power supply, which can only be achieved by aggregating many pins. System-on-chip (SoC) designers can use a dedicated secondary PMIC off-chip to provide individual low-voltage, low-current power rails, thus avoiding the extra die and cost benefits of on-chip power management design.

　　Power management needs vary

　　Smartphones are widely adopted around the world, and the market is becoming more diversified. To provide consumers with more choices of models, suppliers are gradually expanding from the high-end market to the entry-level market, but they are under great pressure to launch new models every 6-9 months to meet consumers' demand for the "latest and best features" and competition from peers. At this time, the design method of smartphone platforms becomes increasingly important. The new platform strategy allows them to manage these processes and reduce costs.

　　The industry has also observed a trend of smartphone suppliers and SoC companies working together to lay out the market. These SoC companies can provide original equipment manufacturers (OEMs) with a complete reference platform architecture to help accelerate product launch time and reduce development risks. Of course, a very important point for OEMs is whether they have the ability to tailor the platform and develop differentiated products based on market demand.

　　The industry's introduction of a highly configurable PMIC allows suppliers to be more flexible in designing smartphone platforms and launching multiple models and designs for different market needs throughout the product life cycle. It can support late changes in circuit board design when additional features are added to the smartphone platform during the R&D process. This also helps reduce PMIC inventory and meet the consumer electronics market's demand for quantity flexibility. For new mobile phone suppliers, this customized feature enjoyed by working with SoC suppliers can be a huge advantage.

　　PMIC Coordinates Multi-Core Device Process

　　Most smartphones today use single-core and dual-core SoCs, with a few quad-core models in high-end products, and the same is true for the tablet market. However, the larger power requirements (passive cooling requires 4 watts (W), systems with fans require 7-8 watts, while smartphones only require about 1 watt) mean that processors will move towards higher core counts.

　　Some people question the need for multi-core mobile computing devices. It is true that most personal computers sold on the market today have dual-core central processing units (CPUs), but since most software applications are single-threaded rather than multi-threaded, they cannot run on multiple cores. Software for mobile devices is even less suitable for multi-threading.

　　Still, the power benefits from multi-core devices are significant. Multi-core devices assign simple tasks to one core while directing more complex, power-hungry tasks to other cores. Each quad-core or octa-core application processor must be powered up and powered down from sleep in a specific order. The PMIC acts as a system conductor, telling individual circuit blocks in each baseband or application processor device when to wake up and when to go to sleep to save power. Most workloads are still single-threaded and run at high frequencies, so the SoC must be able to efficiently deliver total processing power and single-core performance.

　　Heterogeneous cores, which ARM labels big.LITTLE, pair a small but efficient core with a larger and more complex core, and can switch between the two. Mobile devices must reduce the power losses caused by switching through efficient power management solutions. In short, if every circuit block has to be in high-performance mode at the same time, there will not be enough power or heat dissipation. When running a highly realistic and interactive game, the display and graphics processor (GPU) will use most of the power; the CPU must reduce frequency and voltage to provide the best overall performance. If there is also significant wireless data traffic, everything will become more complicated. The end result is that an advanced PMIC is required to handle the switching of these processes.

　　LTE and the Power Efficiency Challenge

　　LTE smartphones also present power efficiency challenges. Today’s digital module technology can compress more data bits into each RF channel, resulting in more complex waveforms with higher crest factors (peak-to-average-power-ratio, PAPR).

　　LTE signals have very high crest factors (typically 7.5-8dB PAPR), resulting in high peak power requirements for the transmitter. Traditional fixed voltage power amplifiers (PAs) are extremely energy efficient when they are in compression at the peak of the transmit waveform. If designers prefer to use larger supply voltage PAs that can be ramped up, much energy will be wasted and the usable time of an LTE device may be reduced to less than an hour before the next battery charge.

　　To optimize power efficiency, two auxiliary PMICs must be used to manage the more complex voltage and current requirements of smartphones. Envelope Tracking is also an emerging and promising power supply technology that can be used to improve the energy efficiency of the RF power amplifier (RFPA) of LTE mobile phones. It replaces the fixed DC voltage supplied by the RF power amplifier with a dynamic supply voltage, which can more closely track the amplitude, or the packet of the transmitted RF signal.

　　The goal of packet tracking technology is to improve the efficiency of power amplifiers carrying signals with high peak-to-average power ratios. To provide high data processing capabilities within limited spectrum resources, linear modules with high peak-to-average power consumption ratios must be used. Unfortunately, traditional power amplifiers with fixed voltage sources operate inefficiently under these conditions. In a packet tracking power amplifier, the efficiency can be improved by changing the power amplifier supply voltage in sync with the packets of the radio frequency signal.

　　Save PCB space by integrating audio chip into PMIC

　　OEMs are also under pressure to save board space. They must free up more area to accommodate new features while keeping the device thin and short and reducing costs. For these goals, the use of three-dimensional (3D) packaging or chip stacking technology can produce advantages. Generally speaking, chip stacking uses low-density wiring or solder bumps to connect different stacked layers. The industry integrates or stacks fully configurable PMICs and low-power audio codec chips (Audio CODEC) in a single package, integrating more than forty different high and low voltage circuits and analog functions on a single chip, greatly saving board space and cost.

　　In addition to saving space, the industry's first audio codec chips also provide ideal audio performance for consumer devices. By integrating advanced echo cancellation software into the digital signal processor (DSP), the audio codec chip can filter out background noise and increase sound clarity, thus providing rich, low-frequency and high-definition frequencies even in noisy environments.

　　In addition to chip stacking technology, the industry will see other new technologies to save circuit board space in the future. One of these technologies is 3D integration, which connects different circuit layers through through-silicon vias (TSV). TSV is denser and provides stronger connectivity, can span more layers and save more power. 3D integration was initially used to package high-speed memory and SoC to provide better bandwidth for graphics functions, and it is now definitely an area worth watching in the future.

　　Thin and light features may cause high leakage current

　　Mobile devices are becoming thinner and smaller, yet packing more functionality than ever before. Smaller device sizes can lead to dangerously high leakage currents due to short channel effects and different doping levels, which ultimately prevents the industry from moving towards smaller sizes.

　　In addition, the emergence of new stacked materials such as high dielectric constant metal gate (HKMG) and fully depleted transistors such as fin field effect transistors (FinFET). Today's FinFET is a 3D structure that rises on a planar substrate. Compared with a planar gate of the same area, FinFET can provide greater capacity. The gate around the channel can provide excellent path control, so that when the element is in the off state, the leakage current that can pass through the body is negligible. This makes the use of low threshold voltage values ​​feasible to achieve optimal switching speed and power.

　　There are many other promising technology blueprints. For example, Dialog and TSMC are working together on the most advanced 0.13 micron (μm) Bipolar-CMOS-DMOS (BCD) technology to integrate advanced logic, analog and high voltage components in a small single-chip power management chip to support the next generation of smartphones, tablets and Ultrabooks.

　　BCD process technology represents the innovative force that drives all areas of the semiconductor industry, including applications, design and process advancement. This technology combines analog bipolar (B) devices, complementary metal oxide semiconductors (CMOS) and double diffused metal oxide semiconductors (DMOS) on the same wafer. System designers use this technology to reduce power losses, circuit board space and costs. This technology helps to manufacture better, smaller and more innovative products. At the same time, because BCD technology is now manufactured on 6-inch wafers, wafer fabs can allow their almost depreciated production lines to continue to contribute productivity, which can reduce costs and generate profits for end customers, or have more room to invest in other emerging technologies.

　　DC-DC power converters are the foundation of today's power management integrated circuits. The industry-patented TIPS (Transformative Integrated Power Solutions) technology uses a unique conversion method based on exchange capacitor technology. This technology allows the use of smaller conductive components, which in addition to improving efficiency, can achieve higher overall power density than competing technologies, providing significant advantages for portable and data center applications.

　　Power management determines brand success or failure

　　According to industry forecasts, the demand for mobile computing devices continues to increase. Mobile devices are evolving from personal information devices to mobile computing platforms, playing an increasingly important role in daily needs. At the same time, power performance is quickly becoming a key issue of this era. Smartphone users who are highly satisfied with their phone's battery life are more likely to buy the same brand of phone again than those who are dissatisfied. Among 4G smartphone owners who are highly satisfied with their phone's battery life (selecting 10 points on a 10-point scale), nearly 25% said they would "definitely" buy a phone from the same manufacturer again. In contrast, only 13% of phone owners who are less satisfied with their phone's battery life (selecting 7-9 points on a 10-point scale) expressed the same intention. Mobile phone operators who overcome challenges by adopting innovative power management methods in their devices can gain a greater competitive advantage and market share over other mobile phone operators.

　　Consumers want more devices in their lives. For example, a small number of consumers who purchase 3G or 4G plans for tablets would rather use wireless local area networks (Wi-Fi) to receive and consume media at home or work. Regardless, it is clear that consumers want unlimited wireless connectivity. Such requirements put greater pressure on the battery life of portable devices, and the industry must continue to focus on power management innovation for triple-network smartphones, tablets, and the new hybrid tablet laptops that are about to be launched.