The smartphone is one of the most widespread and versatile devices in the modern world. It has gained immense popularity over the past decade and now acts as a primary interface with the digital world. In some cases, especially in developing countries, a smartphone could be a user’s lone computing mechanism. Just 10 years ago there weren’t quite 4 million smartphones shipped to date. In contrast, in 2017 and beyond IHS Markit expects over 1.5 billion of these devices to ship globally each year. Many of the more user facing smartphone functions such as the screen, camera, memory, processing, and software are widely talked about in the market today. However, the function of the RF front-end (the components between the transceiver and the antennae), one which essentially enables the mobility of a smartphone, is often overlooked. RF performance can be an enabler of or barrier to a great mobile broadband experience.
Since the onset of the widespread adoption of LTE technology, the RF front-end (RFFE) has been supporting an increasing number of frequency bands and air interface modes while overcoming size and cost limitations set by the other areas of smartphone design.
Whereas the transition from 2G to 3G technology resulted in a geometric increase in RFFE complexity, the move from 3G to 4G has exponentially increased the complexity of the RFFE with developments such as 4x4 MIMO antenna architectures and carrier aggregation, in addition to an increase in frequency bands. Concurrently, in an increasingly competitive environment OEMs may be focused on most of the aforementioned user facing functions and may have more limited interest in the RF Front-end during a time when the function is more important than ever.
According to IHS Markit Wireless Semiconductor Competitive Intelligence Service, the value of the mobile handset RF front-end component market has grown from $4.3 billion in 2010, before the rapid adoption of LTE technology, to an estimated $13.4 billion in 2017; a compound annual growth rate of over 17.7%. During this time the RF component market grew at a rate 5 times higher than the overall semiconductor market, an amazing achievement that highlights the growing importance and complexity of the RF front-end.
In order to shed some light on one of the most critical aspects of smartphone design, the RF front-end, IHS Markit will be producing a series of RFFE Insights. These articles will discuss the trends of component integration, increasing complexity, and some of the key technological attributes which will be required for superb RF performance as the market progresses further toward the adoption of 4G+ and 5G technologies. This article is the first in the series.
The Progression of LTE has driven the RF Components Market
As the number of frequency bands serving LTE has expanded, techniques such as carrier aggregation have emerged to push data rates even higher. Carrier aggregation is the combining of separate RF bands to create wider bandwidths and faster download and upload speeds for a given device. The technology arose with LTE-Advanced which is essentially any device rated LTE Category 4 or higher. Beginning with Cat 4 LTE, devices can achieve data rates of 150 Mbps or more. The latest available modems are Cat-16 LTE and are capable of downlink data rates of around 1 Gbps. Coming next year, Cat-18 devices will be capable of even faster data rates of 1.2 Gbps. In order to achieve these remarkable speeds, mobile devices have had to support more transmit and receive paths, the additional receive paths have particularly grown more complex with 4x4 MIMO designs and will need to support a growing number of carrier aggregation band combinations. As LTE Advanced progresses into LTE-Advanced Pro, the number of carrier aggregation combinations is growing exponentially, where there were only 200 CA combinations in 2015, two years later the stage is set for more than 1,000 band combinations.
Component Integration to Limit SKU Proliferation
A decade ago smartphones only had to support around five frequency bands in order to be considered “world phones”, now with LTE, there are around 50 frequency bands, before even accounting for the possible carrier aggregation combinations. Just a few years ago it was possible for OEMs to release a single SKU global smartphone, albeit this was a challenge even then. Most smartphones released today have at least 2 to 4 variants to address all the major networks across the globe. Apple has been the only high volume premium smartphone OEM to achieve a single global SKU with the iPhone 4S, however, that will likely be the last time this will be achieved by such a high volume device, especially as LTE has progressed. With the 4S Apple only had to contend with 3G technology which was still deployed on a relatively small number of frequency bands, once Apple made the move to LTE, the single SKU was no longer an option and by the end of September 2012 there were three different models of the newly released iPhone 5, each addressing a different set of LTE bands. Smartphones have limited space for RF components and in order to support a growing number of frequency bands, these components must integrate with one another into modules. Additionally, components like power amplifiers (PA) must not only support a set of frequency bands but multiple modes as well. These multi-mode, multi-band PA are surrounded by other components such as RF switches, duplexers, and filters to create integrated front-end modules.
Examining what an earlier LTE smartphone RF front-end looked like compared to today’s flagship smartphones highlights the magnitude at which component integration has taken place. For instance, only 6% of the major RF components found in the Samsung Galaxy SIII in 2012 were integrated within modules while these components accounted for 26% of the RFFE bill of materials (BOM) cost (not including the RF transceiver). In contrast, modularized components accounted for 87% of the RFFE BOM in the Samsung Galaxy S8 Plus.
Not all OEMs will use the same approach toward RF component integration, depending on the target markets for a smartphone; they may choose to utilize a mix of discrete and integrated RFFE products. RF suppliers such as Skyworks, Qorvo, and Qualcomm offer various levels of integrated RF components. For OEMs focused on entry level, local, or carrier specific phones; they may choose to utilize more discrete RF content for their designs. However, even with regionally focused phones, there has been a greater degree of modularization. For regional handset SKUs, OEMs may utilize the integrated approach for PAs and switches but stick to discrete filters and duplexers. Front-end modules (FEM) combining switching and filtering content may be used in the receive diversity path as well to facilitate carrier aggregation. In addition to the receive diversity FEM(s), for most global flagship smartphone designs OEMs are turning to integrated front-end modules for the primary transmit and receive section, some of these designs can cover sets of low, mid, and high bands supported by the smartphone. In general, there will be a direct relationship between the level of integration in an RFFE and the BOM cost of the RF section in otherwise similarly designed and priced smartphones.
In the March to Modularization, Filters are beating the Drum
Though the components in a smartphone are becoming increasingly modular, the number of filters used in each unit is expected to go up over time. For each RF band supported by a mobile handset, there can be two or more filter die. Thus, the number of filters (integrated or otherwise) per handset will continue to increase over time, with some phones supporting more than 30 LTE frequency bands with a single model, there could be upwards of 70 filters in a single phone, this is a trend which will continue, especially in the premium smartphone segment. In order for a handset to accommodate the number of filter die required going forward the RF filters will need to be further incorporated into modules along with other functions such as antenna switches and power amplifiers.
System Level Expertise: Winning in RF Takes More than Component Integration Alone
With current premium tier smartphones supporting so many bands and modes, the need for RF suppliers to have system level expertise has never been greater. The most successful RF suppliers will be those which have diverse product portfolios with system level co-design capabilities ranging from the digital baseband to the antennae. These suppliers will be able to address the widest range of customer needs. These needs include producing the most power efficient devices but also offering the fastest possible and consistent download and upload speeds in a given smartphone. Additionally, OEMs must address the needs of mobile network operators to make their devices interact with the network in a manner as efficient as possible. Very few suppliers have the ability to accommodate the entire RF front-end function with their product portfolios, which is a primary reason that only a few vendors dominate the mobile handset RF component market.
The current, integrated RF front-end designs seen in the smartphone market will become foundational during the smartphone’s transition to supporting 5G technologies over the next few years. As new radio designs materialize, and become increasingly software controlled, the RFFE will have to support an even wider set of frequency bands. The range of RF frequency will be expanding from 700MHz-5GHz to 600MHz-60GHz; although higher frequencies will be focused less on mobility. There will also be higher orders of modulation and more air interface technologies which will add to RF complexity. The performance challenges which will surely be brought by 5G can’t be solved by component integration alone and will need to be addressed on a system level as well as within the RFFE. Going forward, the RFFE must be optimized for system level tunability in general and technologies such as envelope tracking and antenna tuning will be necessities in order for devices to match user expectations of performance, power efficiency, and battery life. In the next article in this series, IHS Markit will dive deeper into envelope tracking technology, why it’s important, and its current and future prevalence in LTE devices across the globe.