Global data usage has skyrocketed since the launch of the first smartphones. In 2010 the figure stood at just 2 ZB. Fast forward to now and it has reached 120 ZB and this figure is predicted to increase by a further 150% by the end of 2025. It is estimated that 90% of this data was generated within the last two years and with IoT coming to fruition and 5G going mainstream, global data generation is only going to intensify.
This unprecedented growth is having a profound impact on the way mobile phones are designed and built, particularly their mobile radio front ends. Parameters are constantly changing; functionality is becoming increasingly complex and the physical space they occupy within the overall design is expanding. The total size of a mobile device, however, is finite and as such printed circuit board (PCB) space is now one of the most valuable and sought after areas. No longer limited to voice communications, today’s smartphones have evolved into multimedia hubs that enable us to interact with technologies and applications in ways unimaginable just a few years ago.
More frequency bands, more hardware
The introduction of the 4G standard initially paved the way for high data demand. 5G, with its promise of ultrafast upload and download speeds magnified the situation, which in turn heighted the need for more spectrum and more frequency bands to be made available. However, it is somewhat ironic that the proliferation of new frequency bands, intended to alleviate bandwidth scarcity and increase network capacity has only intensified the PCB space dilemma in smartphones and other mobile devices. More bands require more distinct components; power amplifiers, filters, duplexers, switches etc for basic communications purposes, resulting in larger, more complex radio front ends. In parallel, there is heightened market demand for evermore powerful and compact smartphones with advanced features and greater functionality. Factor in the drive for bigger screens, faster processors, memory boards, high power batteries and sophisticated cameras then something needs to change to optimise the available PCB space.
Limitations of fixed frequency filters
When the first smartphones were launched in the late 1990s/early 2000s two frequency bands were in use. From a communications perspective this meant that 4 x filters were needed: 2 x transmit, and 2 x receive filters so signals can be isolated from each other. Each pair of filters makes a single duplex filter. By 2010, support for 8 x frequency bands was required. Fast-forward to now and the average smartphone must include 32+ duplex filters to support 32+ bands and this figure is increasing.
Fixed frequency duplex filters are fundamental to the operability of all wireless devices in their existing formats. They ensure that the built-in transmitters and receivers can simultaneously send and receive radio signals so we can listen and speak to each other. They also prevent self-interference (an unavoidable consequence of wireless RF) from compromising performance and efficiency of the device. Failure to keep this self-interference in check will render any mobile device unfit for purpose.
What this means from a PCB perspective:
- Each frequency band requires a fixed frequency duplex filter supported by selector switches
- Each packaged duplexer is ~1.6×1.2mm
- 30 duplexers take up ~ 66 mm2 of PCB space (including 100µm spacing between filters, no routing)
The impact of third-party technologies
The wireless communications landscape has evolved significantly since the advent of the smartphone and our growing data dependency. This, combined with the introduction of 3G, 4G and 5G standards has given rise to the development of advanced signal processing technologies such as Carrier Aggregation (CA), Multiple-Input Multiple-Output (MiMo) and Diversity to support operator demand for additional capacity. These different technologies collectively, however, have magnified the complexity challenges in mobile radio front ends, further cementing the need for a rethink.
Why miniaturization is important
One possible way to reduce the overall PCB space in mobile radio front ends whilst maintaining optimal performance is to leverage tunable duplexer technology. Tunable duplexers are designed to be versatile and adaptive so they can support multiple frequency bands within a device’s operating range. As such they empower OEMs to achieve notable reductions in the size and complexity of mobile radio front ends, enabling the development of compact and efficient mobile devices with a greater number of features for competitive differentiation. Other benefits include streamlined supply chain, reduced manufacturing costs, frequency agnostic capabilities and support for sustainable processes.
Resolving the self-interference quandary
The key to the effectiveness of tunable duplexers lies in their ability to dynamically adjust their resonant frequencies. Until now tunable duplexers have comprised varactor diodes, MEMS (Micro-Electro-Mechanical Systems) technology and other tunable components. These elements are electronically configured to match the desired operating frequencies, eliminating the need for fixed-frequency filters for each supported band. However, these classic implementations do not have sufficient performance to meet [mobile phone / 3GPP / wireless] specifications. More significantly, they allow too much of the transmit signal to leak into the receiver, preventing the receiver from working correctly. These challenges need to be overcome before tunable duplexers can be utilised in mass manufacturing processes. The race is on to achieve this because simply increasing the number and types of components needed per mobile device to match the growing number of frequency bands is untenable long term.
Conclusion
As demand for compact, high-performance smartphones continues to escalate and band counts continue to increase, tunable duplexers do offer a promising solution to the PCB challenge. Moreover, if the self-interference issues can be resolved, they are poised to redefine the mobile manufacturing landscape as we know it by shrinking mobile radio front ends whilst maintaining or even enhancing their functionality.
