RF discrete component approaches, module architectures, and circuits challenged as the mobile industry moves to next-generation networks
Until the deployment of early LTE networks, the design of the RF system was fairly simple and straightforward, as it involved a relatively small number of front-end components. The design of the RF front-end has since become increasingly more complex with the upgrade to LTE-Advanced. These technologies have enabled 4G networks to become efficient and reliable through the use of carrier-aggregation, MIMO, diversity, and envelope tracking.
The need to support a multitude of LTE bands in myriad combinations across the globe has amplified RF design complexity, leading to the addition of a greater number of RF components needed to support these bands and permutations. In the very constrained environment of smartphones, in terms of both energy and overall form factor, the RFFE system needs to be meticulously designed in order to optimize the overall performance of the device and mitigate interferences. This needs to be achieved without compromising the integrity of its industrial design, reliability, and ability of the device to support innovative features and functionalities.
The RFFE design is expected to be even more complex as the industry moves toward LTE-Advanced Pro and 5G. These networks will require additional RFFE functionalities, including higher order MIMO and massive MIMO, smart antenna systems, and sophisticated filtering functions. To put this into context, a high-end smartphone today, supporting 2X carrier aggregation, has around 7X the number of discrete RFFE components compared with a standard 3G device, and this number is poised to double with the move to LTE-Advanced Pro and could more than quadruple as networks migrate to 5G.
A design balancing act
Until now, and despite the increases in complexity, the physical RF footprint area on a smartphone has been reduced through three main approaches:
- Lowered footprint semiconductor process: This development has enabled some discrete components to shrink massively over the last few years. For example, the use of new materials, such as gallium arsenide (GaAs) and silicon germanium (SiGe), has enabled power amplifiers to be reduced in size, as opposed to previous generation technologies. Equally, the size of current-generation transceivers and LNAs has decreased due to the use of lower footprint semiconductor process technology, g., the use of 28 nm and below technologies.
- Improved packaging technologies: New packaging technologies, such as Chip-Sized SAW Packaging (CSSP), Die-Sized SAW Packaging (DSSP), Thin-Film Acoustic Packaging (TFAP), CuFlip, and Wafer-Level Packaging (WLP), enable many RF components, including filters, duplexers, and multiplexers, to shrink substantially. In addition to component-level miniaturization, these technologies also offer significant cost savings at the system level through reduced bill of material and simplified integration with other components, including antenna switches and transceivers.
- Increased physical integration of components: Integration and modularization of the main RFFE components, such as filters, PAs, duplexers, and switches, have continued apace, with the supply of bundled solutions from companies such as Murata, Skyworks, Avago, EPCOS, Qorvo, and Qualcomm. These approaches are critical for reducing the overall size of the RFFE by bringing certain homogeneous components together in a single package.
The concept of physical integration is being extended further with new packaged solutions, such as front-end module with integrated duplexers (FEMiDs) and PA module integrated duplexers (PAMiDs) that bring together a variety of components like PAs, switches, transmitter low-pass filters (LPFs), and receiver SAW filters into front-end modules. While not all RFFE components can be subjected to bundling due to their heterogeneous nature and interference, these newer types of integrated modules aid with lessening complexity, while reducing footprint size.
In addition, there is a clear delineation between the use of discrete components for smartphone SKUs at the entry level and those for global SKUs that have higher levels of component integration and meticulous RFFE design, offering superior performance. The majority of the world’s largest OEMs are looking increasingly to provide a single global SKU for their flagship models to reduce operational cost and harmonize experiences, and this goal is being helped extensively by the use of PAMiDs. Similarly, OEMs do not want to commit to providing a host of country SKUs in their portfolios, and so FEMiDs allow the ability to create different regional SKUs with easily substituted modules offering support for differing bundles of RF bands.
Moreover, the increase in RFFE complexity and its associated hardware has a perceptible effect on smartphone industrial design. Handset vendors have to ensure that their devices are capable of integrating these high-end technologies, and their RFFE requirements, into smartphones without compromising any of the following:
- Time to market
- Price
- Performance
- Power consumption
- Established designs (g., dimensions, thinness, display size, use of metal covers, etc.)
Any significant delays experienced by vendors’ smartphone models could prove disastrous, notably at a time when it is crucial for OEMs to stay competitive as the smartphone market is maturing and enduring cutthroat competition. More crucially, it is these next-generation networks that they are pinning their hopes on for creating a much-needed market boost to stimulate upgrade and replacement cycles.
This shift to new network technologies creates additional challenges to those companies providing RFFE architectures and components with many along the value chain currently engaged in finding the most optimal and cost-effective RFFE solutions to make this increasing complexity easier to manage. It is here that the use of standardized RFFE modules and help from end-to-end solutions providers will provide welcome support to OEMs, which will help greatly with the RFFE design process and speed time to market. However, as uncovered from analyses of smartphone models featured in ABI Research’s Teardown service, there is a link between RF system enhancement and the size of its silicon board area. In other words, for similar RF design, one should expect the size of the RF board area to increase significantly as the system supports new enhancements and accommodates new components. However, the use of well-designed RF systems could make the RF board area more compact and smaller in size. The Samsung Galaxy S8, which features many advanced RF components, including 4xCA DL, 2xCA UL, 4×4 MIMO, dynamic antenna tuning, and envelope tracking, is a good example of handling the RF complexity. It is clear that most handset vendors are struggling to cope with this increase in RFFE burden and no standard implementation has yet been pursued. Under current conditions, some are even delaying model launches in a bid to get a useable product to market, or else risk the device not working effectively. Issues include having a significant increase in power consumption, due to the front-end components, or compromising on the industrial design.
In contrast to the OEMs, RF component manufacturers are under pressure to customize their products and comply with smartphone vendors and operators’ requirements, significantly impacting their overall margins. This threat to their business has been tempered somewhat through RF supply chain rationalization, such as the formation of Qorvo borne out of the merger between of TriQuint Semiconductor and RF Micro Devices, and the creation of RF360 Holdings, a joint venture formed by Qualcomm and TDK EPCOS. In addition, Murata’s acquisitions have enabled it to gain access to PA and RF switch technologies, allowing it to now seamlessly manufacture all key RFFE components in-house. More industry consolidation and partnerships are to be expected over the coming years due to this drive toward deeper RF systems integration and the clamor for market share.
RFFE leadership demands component and system-Level innovation and integration
It is clear that hardware integration of RF components is necessary for bringing next-generation network technologies to smartphone reference design. Unless more collaboration and targeted integration happens in the RF industry, handset vendors will face an uphill struggle to overcome the challenges that the RF poses, which can only get worse as higher-order CA, 4×4 MIMO, and 5G penetrate the smartphone market further, with the potential to hamper both industrial design and power management.
However, while the availability of comprehensive, high-performance RF components and modules is important, they have yet to fully reach mass market devices. Additional RF innovation will also be required to produce the next generation of mobile devices that will be packed with many new network technologies and features. As the market moves toward LTE-Advanced Pro and 5G, the physical integration of components will not be enough to address the RFFE challenge head-on, so highly-integrated RF system design will be the key to help aid this transition.
Indeed, RFFE system design and platformization will become vital in the drive to accommodate a host of additional heterogeneous components into smartphones, such as MIMO systems, intelligent antenna systems, and beamtrackers, which are a consequence of moving to next-generation networks. As the RF systems grow in complexity at both the downlink and the uplink layers, the integration of new system-level technologies, such as envelope trackers and dynamic antenna tuners, will become a necessity for improving the overall RF system performance. This will become increasingly self-evident as additional spectrum bands, including C-band, mmWaves, and cmWaves, will be switched on to support 5G, which will create even more opportunities and challenges in terms of RF solutions and design.
Industry stakeholders must grasp the opportunity to provide advanced RFFE system designs through providing not just the core set of RFFE technologies and advanced module integration, but also modem-to-antenna RF solutions. These high-end solutions will fulfill a need that the smartphone industry desperately craves, enabling OEMs to focus on customer experiences and deliver more reliable devices to scale and on time, negating their need to deal with a proliferation of future component types and suppliers.
The most likely breeding ground for these RF designs is system integrators, such as Qualcomm, Intel, Tsinghua (which is the holding company for Spreadtrum and RDA), Samsung, and Huawei, rather than the traditional RF component suppliers. Currently leading the way is Qualcomm. Not only has the company managed to create new modem-based RFFE technologies, such as envelope tracking and antenna tuning, but it has also created a highly-integrated packaged RF solution through piecing together a number of targeted acquisitions and joint ventures to plug the gaps in its RF knowhow, including TDK (Epcos), Nujira, and Black Sand.
Such an approach puts the company in good stead to meet the upcoming challenges of 5G and will be a requirement of others along the supply chain if they are to survive. It is essential that they are able to provide smartphone vendors with the tools needed to create next-generation devices. Indeed, it is expected that, over the next 12 months, key suppliers and systems integrators will increasingly absorb specialized vendors and some components suppliers, while competition in the market may push some RF component vendors to exit the smartphone market altogether.
