MWJPerspective Evolution of the Smartphone Todd Gillenwater, Mobile Products CTO and VP of Engineering Qorvo, Greensboro, N.C. n less than 10 years, mobile Ride-sharing companies like Uber smartphone designed for global phones have evolved from rely on the ubiquity of mobile de- use may support more than 30 tools used mostly for talking vices that let users find and pay for bands today, compared with fewer and texting to highly complex, rides that are automatically direct- than 10 in 2010. The trend is con- Isophisticated devices that are cen- ed to their locations. tinuing, as regulators allocate new tral to almost every aspect of our All of these applications mean that higher frequency bands at 3.5 GHz lives. They have changed the way high speed, highly reliable data con- and above and refarm existing we communicate, letting us share nections are essential to everyone’s spectrum, such as the 600 MHz experiences in real time by upload- daily life. Demand for mobile data band previously used for TV broad- ing and downloading live video. continues to grow rapidly: the No- casting. Channel bandwidth has in- They guide us while driving, mak- vember 2016 Ericsson Mobility Re- creased, from 200 kHz with 2G to ing paper maps almost port predicts that global smartphone 20 MHz with 4G, even more using obsolete. They have subscriptions will rise from 3.3 bil- carrier aggregation (CA) in LTE Ad- become univer- lion in 2015 to 6.8 billion in 2022, vanced (see Figure 1). This is be- sal controllers with the data used per smart- ing combined with techniques for for Internet of phone expected to rise nearly 8x producing higher data rates and Things (IoT) to 11 GB/month over the same capacity from a given bandwidth, devices rang- period. Trends such as virtual re- such as MIMO, more complex ing from home ality and real-time video require modulation and network densifi- thermostats high performance networks cation, including the use of small to hotel room that provide low latency as well cells. door locks. as higher data rates. Today, key trends include LTE And they have To handle the growth in mo- Advanced, which network opera- enabled com- bile data, successive network tors are now deploying, and its panies to create generations—2G, 3G, 4G (LTE) successor LTE Advanced Pro (de- entire new cloud- and, in the future, 5G—have used fined in 3GPP Release 13 and based business a variety of methods to progres- later releases). These LTE network models. sively increase network enhancements ensure that 4G will capacity and data continue to play an important role rates. One way even after 5G begins to be de- is allocating ployed. LTE will operate in paral- many more lel with 5G and provide adequate frequency performance for many applica- bands. tions. LTE Advanced introduced A flag- CA, which aggregates the band- ship LTE width of up to five RF carriers, Reprinted with permission of MICROWAVE JOURNAL from the February 2017 issue. ©2017 Horizon House Publications, Inc. MWJPerspective TABLE 1 COMMON CELLULAR BANDS 1 Gbps 600 Mbps Band Uplink (MHz) Downlink (MHz) Duplex Type 4 CA ate 450 Mbps 2 × 2 MIMO 1 1920 to 1980 2110 to 2170 FDD R 3 CA Cat 11/12 3 1710 to 1785 1805 to 1880 FDD ata D 300 Mbps 2 × 2 MIMO 4 1710 to 1755 2110 to 2155 FDD 20 + 20 MHz Cat 9 150 Mbps 2 × 2 MIMO 7 2500 to 2570 2620 to 2690 FDD ownlink D 10 + 10 MHz Cat 6 2 × 2 MIMO 17 704 to 716 734 to 746 FDD 25 1850 to 1915 1930 to 1995 FDD 2013 2014 2015 2016 40 2300 to 2400 2300 to 2400 TDD 41 2496 to 2690 2496 to 2690 TDD Fig. 1 Increasing downlink data rate enabled by carrier s 66 1710 to 1780 2110 to 2200 FDD aggregation. called component carriers (CC). between different bands, between LTE Advanced allows maximum the transmit and receive frequen- network data rates up to 1 Gbps, cies of each frequency division du- Third and LTE Advanced Pro will increase plex (FDD) LTE band and between Harmonic the possible number of CCs to 32, LTE and other wireless services, allowing up to 3 Gbps. Wi-Fi is be- such as Wi-Fi and public safety coming more important with the communications. High perfor- introduction in LTE Advanced Pro mance acoustic filters are needed Uplink Downlink Downlink of licensed assisted access (LAA), to achieve the required isolation. Band 17 Band 17 Band 4 which uses CA to combine licensed Bulk acoustic wave (BAW) filters LTE spectrum with unlicensed Wi- provide better performance (high- Fi spectrum at 5 GHz to achieve er Q factors) than surface acoustic s Fig. 2 With carrier aggregation, the greater data rates. wave (SAW) filters, especially at third harmonic of the Band 17 uplink higher frequencies, and are typi- signal can interfere with the receive SMARTPHONE TRENDS AND cally used for the most demanding signal in Band 4. CHALLENGES applications. As smartphone data perfor- The isolation challenges increase interference, the filters in the RF mance requirements continue to with CA, because the RF front-end front-end must provide very high grow, so does the complexity of must communicate simultaneously rejection of the problem harmon- the RF front-end, creating a series on multiple bands. This leads to ics without adding unacceptable of new challenges for the engineers new requirements for cross-isola- insertion loss. High linearity is re- working on smartphone designs. tion between bands, to avoid situ- quired in all the components— Today’s requirements are creat- ations where the transmit signal of PAs, switches, filters—to minimize ing design challenges that include one aggregated band interferes the generation of harmonics. maximizing linearity and isolation, with receive signals on another ag- A different cross-isolation issue managing power consumption and gregated band, which will degrade occurs when aggregating closely antenna tuning. Greater integration the sensitivity of the receiver. There spaced bands, which typically is required, since an increasing num- are various problem scenarios. share the same RF pathway within ber of bands must squeeze into the When aggregating widely sepa- the RF front-end. Examples include limited space allocated to the RF rated frequency bands, issues can bands 1 and 3 and bands 25 and front-end. Another important trend arise with harmonic frequencies 66. In these cases, the problem is is the emergence of smartphone generated at multiples of the trans- that the transmit frequency of one market tiers, each with differing RF mit frequency by non-linear com- band is close to the receive fre- requirements. This article discusses ponents in the RF chain, including quency of the other aggregated each of these and how the smart- power amplifiers (PA), switches and band. Multiplexers, which combine phone will evolve to handle 5G. even filters. With some band com- all the transmit and receive filters binations, such as bands 17 and 4 for multiple aggregated bands into Isolation (see Table 1), the third harmonic of a single device, provide an effi- The requirement to accommo- the lower frequency band (17) falls cient solution, allowing simultane- date more LTE bands within the into the receive frequency range ous use of the aggregated bands RF front-end creates challenges of the higher frequency band (4), while providing isolation between achieving the necessary isolation as shown in Figure 2. To prevent them. Multiplexers will become MWJPerspective increasingly important as network operators aggregate three or more Hexaplexer bands (see Figure 3), due to limits Band 1 on the available space and number Quadplexer Tx of antennas within the smartphone. Band 1 Band 1 Tx Rx Power Management Duplexer Single Filter Band 3 Band 1 Band 3 Several trends require better Rx Rx Tx Common Band 3 Common Common Common power management to maximize Port Rx Port Port Port smartphone battery life and avoid Band 3 Band 3 Band 3 Tx Tx Rx overheating. Greater transmission bandwidth, achieved with tech- Band 3 Band 7 niques such as uplink CA, will re- Rx Tx quire more power. Also, intra-band Band 7 uplink CA, which combines compo- Rx nent carriers within a single band, involves higher peak-to-average s Fig. 3 Multiplexers become increasingly important as network operators aggregate power ratios than standard LTE sig- bands to increase data rates. nals, increasing the demand on PA linearity. For example, doubling the a Network Problem” in this issue, space allocated to the RF front- uplink bandwidth with CA to 20 + page 102.) end has not increased. In today’s flagship phones, typically only 10 20 MHz (200 resource blocks) more Antennas than doubles the probability that to 15 percent of the internal area the peak-to-average power ratio of The number of antennas in is dedicated to cellular, Wi-Fi and the modulated signal envelope will smartphones has grown with the Bluetooth RF functionality. Smart- exceed 4.5 dB. requirement to support faster data phones are getting thinner, reduc- Another emerging requirement services as well as the growing ing the internal volume, and manu- is Power Class 2, a new standard range of RF frequencies and tech- facturers need to use the available that doubles output power to 26 nologies. Today’s handsets may space for new functionality and to dBm to overcome the greater prop- include as many as six or seven an- maximize battery size to respond agation losses of high frequency tennas, including primary cellular to user demands for longer op- bands (e.g., Band 41). The greater and diversity receive (DRx), Wi-Fi, erating time.