Some Like It Hot, But Not Smartphone Users

Few seem to remember the days of bulky brick or bag phones that at the time seemed like marvels of technology. Those mobile phones could only make phone calls, but today the smartphone is central to many people’s lives, providing a functional substitute for several different standalone devices. The smartphone can act as an ever present camera with DSLR like performance and the ability to record 4K video, a personal navigation system, and an entertainment hub providing for a high quality music and video experience while on the go. Today’s high end smartphones can do things that most analog mobile phone users from the 1990s and before could not even imagine.

Slim form factors with sleek metal and glass bodies exemplify the refined tastes of the smartphone user and not unlike relatively recent buying trends with televisions, smartphone screen sizes have generally increased as well. Users, regardless of which price tier they are interested in, are looking for significant performance increases and additional value with each generation. Although most users are unaware, these increasingly stringent performance and design requirements placed on OEMs produce heat management and power efficiency challenges that are becoming ever more difficult to overcome.

In this article series IHS will highlight the importance of heat management and power efficiency (thermal performance) to smartphone users, OEMs, and semiconductor suppliers alike. This introductory article will cover an overview of the most important underlying factors impacting the thermal performance of any given smartphone which could be summarized with three different aspects of thermal design (“the three S’s”) which consist of:

• System level design – Several device attributes can impact thermal performance such as the materials used for the phone’s casing, the choice to utilize heatsinks or other heat dissipation techniques, PCB layout, internal components, and underlying software, firmware, or protocol stack, etc.
• System on a chip (SoC) design – Thermal characteristics can be affected by the performance of certain IP blocks including but not limited to the CPU, GPU, other peripheral cores, as well as the design of other supporting functions.
• Silicon level design – Technology and process node evolution as well as transistor layout can also have an impact on the thermal performance of a given smartphone.

Subsequent articles in the series will look at each of the three levels of design identified above in more detail and their impact on a smartphone’s thermal performance. Different factors impacting the operating temperature of smartphones will be considered and myths about what creates a hot smartphone will be debunked.

Throughout the series, IHS will examine how OEMs, semiconductor suppliers, and foundries can work together to achieve an optimal balance between ideal thermal characteristics and the overall performance of a device.

The Whole Can Be Hotter Than the Sum of its Parts

From their inception, mobile phones have faced thermal performance challenges with OEMs and semiconductor suppliers finding ways to assuage user concerns about their devices overheating or sub-par battery lives. As might be expected, with user demands continuing to escalate, the difficulty in masking thermal performance has increased as well. Over the past few years the issue of smartphone thermal performance during intense activities has become more visible among the technology-centric media, bloggers, product reviewers, and consequently consumers themselves. Some reviewers of the newest devices are taking into account how hot the devices are during different use cases, and if the individual device is too hot they’ve been quick to lay blame on the OEM or the chipset vendor, when in fact there are many different contributing factors on how hot a phone runs in different situations.

Thermal performance must be accounted for from the very beginning of a smartphone’s development and in several areas of device and system design in order to deliver a product that users will appreciate. A smartphone’s heat signature will vary greatly by the activity of the end user and system level design can help maintain appropriate operating temperature across the wide range of user needs. Use cases which tend to require the display to be active along with moderate or heavy processing to occur, such as gaming can contribute to higher than normal operating temperatures for any given phone. Design elements such as metal casing and large screen form factors are becoming popular choices and may cause phones to heat up more than those with plastic or other casing material and smaller screens but with other similar hardware during these same situations.

Gaming is particularly challenging from a thermal perspective as users are usually holding their phones during this time, making them acutely aware of temperature changes. As high end smartphones are now offering console-like graphics, users are increasingly turning to their smartphones for their gaming experiences making thermal performance an even more important attribute of the smartphone.

Another situation influenced by system level design is the location of the user when performing these tasks relative to the nearest cell site. Devices can heat up based on the users’ location at or near the edge of the cell, as internal components such as power amplifiers have to work harder to maintain not only a minimum network connection but also a connection that can meet the user’s expectation of a high quality of experience.

One of the ways system level design can differ from one OEM to the other is when the signal transmission situation gets better as the user moves further into the cell. Instead of keeping the power amplifiers on at full blast, OEMs can deploy methods of mitigating the impact of the power amplifier on the thermal performance of the device. They may choose to utilize envelope tracking ICs which can dynamically adjust the supply voltage to what is required by the power amplifier in order to maximize power efficiency and battery life, but also reduce heat. Qualcomm currently leads the envelope tracking market along with other traditional RF front-end companies such as Qorvo. These suppliers are using other methods of optimizing power efficiency in the RF front-end including antenna tuning to active RF bands and impedance tuning to mitigate power loss between the antenna and the rest of the RF front-end.

Other internal components such as accelerometers could be used to maximize the power efficiency of a device. For instance, instead of constantly pinging the network for the best connection, a device could leverage the accelerometer to wake up the phone and ping the network when the user changes locations or begins to move.

SoC Level Design – Breaking the Mold

The SoC and supporting components design will impact many use cases for the smartphone user. User experience in scenarios such as 4K video recording can vary greatly depending on the design and implementation of the underlying core IC content of a handset. As device capabilities continue to expand beyond what used to be thought possible for smartphones, it’s becoming increasingly important for smartphone IC suppliers to address thermal performance in every way possible.

The video capabilities of smartphones have evolved at an amazing pace. The first smartphone with 1080p resolution launched in 2012 and only three years later smartphones with 4K displays were a commercial reality. This rate of innovation far outpaces the television industry’s similar move from 1080p to 4K and highlights the potential challenges faced by semiconductor suppliers to maintain operating temperatures while increasing device capabilities.

Watching and recording 4K content have different impacts on thermal performance with the latter leading to higher than normal temperatures, especially as recording time increases. Not only does 4K recording increase the stress on the processor, but the screen is also left on during this time, adding to the thermal challenges presented by this use case. As with larger screen formats, 4K video recording is becoming a more common smartphone feature. Although currently isolated to high-end devices, it is sure to move down into mid-range products in the coming years as well.

Other smartphone features such as “always on” listening or contextual awareness have recently emerged and are providing advancements in thermal performance particularly when it comes to power efficiency and battery life. These evolving functions have led to the implementation of low power peripheral cores such as DSPs as well as sensor hubs. For example, as mentioned above if a phone knows that it hasn’t moved, then there is no need to scan for new cell sites. By having sensors turned on, the phone is able to operate more efficiently using lower power cores and determine if it is necessary to perform high power activities such as scanning for new neighbors. While the aforementioned hardware evolution is increasing the number of sensors within a smartphone, specialized software capabilities are also necessary to manage the various sensors within the device and make them usable for healthcare and accessibility applications, such as heart rate monitoring or advanced voice commands and activation.

The above evolving use cases have resulted in implications for SoC design in order to achieve reasonable thermal performance. One such SoC design element is to use only the processing power that is needed for any given task and shut down higher performance cores when they are not needed or when temperatures rise beyond a given threshold. Many popular SoCs such as Samsung’s Exynos 7420 and the Qualcomm’s Snapdragon 810 perform core throttling. The design of supporting power management functions are also increasingly important as sometimes the battery can cause the device to operate at higher than normal temperatures as well.

All Silicon Is Not Created Equal

Along with SoC design, semiconductor manufacturing has evolved to the point of offering designers benefits of moving to more advanced technology nodes for the main ICs in a smartphone such as the baseband or applications processor. These benefits include an increase in performance and power efficiency. Power efficiency improvements should translate into better battery life and overall thermal performance, but as the move continues to smaller process geometries these improvements have begun to slow based only on linear node shrinks.

A shift from planar CMOS process to FinFET technology is resulting in even greater power consumption and thermal benefits by offering lower variability, and allow for lower voltage operation at smaller geometries compared to planar processes. However performance and power consumption can vary greatly depending on the foundry which is being utilized to produce the SoC. Chipset suppliers such as Qualcomm have begun to move their SoCs to 14nm FinFET with products such as the Snapdragon 820 and 625, while Samsung has had 14nm applications processors commercially available for almost a year now and has since announced their own integrated modem/application processor products on 14nm.

Even with an optimal production process SoC designers face the challenge of OEMs wanting to achieve the greatest performance benchmarks possible for their devices, as such they may tune the SoC to attain the highest metrics as possible without regard to the power efficiency of a device effectively negating benefits gained from any improvements made by the foundry in the production process.

Experimentation Taking Place as Thermal Performance Improvement Continues

Semiconductor suppliers, foundries, and mobile handset OEMs have come a long way in enabling compelling smartphone products that are capable of replacing many consumer devices. Although thermal performance has improved substantially from the days of the old analog mobile phones which offered very limited functionality over and above simple phone calls; it has moved closer to the forefront of user concerns when it comes to mobile devices spurred on by the aforementioned use cases.

As users are coming to expect smartphones in thinner and lighter form factors along with improved performance and richer feature sets in each generation, some OEMs are turning to creative designs to ensure devices don’t get too hot. Mobile handsets such as the Lumia 950 and 950XL by Microsoft are approaching thermal challenges by designing a liquid cooling system in support of the processor, whether or not these unique approaches will result in increased sales still remains to be seen. 

In next article in this series on the contributing factors of smartphone thermal performance IHS will focus more closely on system level design elements and their impact on the user experience of a given smartphone.

The original article can be found here.