Antennas Topologies Directly connecting two duplexers together can affect each other’s filter characteristic, thereby losing the isolation that is needed to operate at reference sensitivity[2]. The duplexer design approach is more complex than the multiplexer design, requiring a separate duplexer for each band and a switch and phase shifters[1].

Antennas Topologies Using the diplexer design reduces the number of antennas required in the user equipment (UE)[1].

Antennas Topologies Mobile devices today have what’s called the diversity antenna, which further increases the downlink data rate[1]. With the addition of MIMO/diversity antennas in LTE, the limited isolation between primary and diversity antennas creates even larger problems for CA[1].

Antennas Topologies For example, IMD products due to the nonlinearity of switch may interfere with diversity received signal because of limited isolation between primary antenna and diversity antenna[1,3].

Understanding Switch Configurations As shown in the previous page, switches are also non ‐ linear components, not to the same extent as PAs, but they can still create harmonics and inter- modulation distortion (IMD) products. Therefore, switches for CA must have very high linearity[1]. Switch isolation is also an important consideration for CA. A switch that supports multiple bands in CA mode must provide adequate isolation between the ports to prevent coupling paths[1,3]. B17 3f0

Understanding Switch Configurations In addition to the B17/B4, there are still some combination leading to harmonics issue, such as B8/B3 (2nd harmonic of B8 Tx 880–915 MHz falls into the B3 Rx band 1805–1880 MHz) and B8/B7 (3rd harmonic of B8 Tx MHz falls into the B7 Rx band 2620–2690 MHz)[7]. The harmonic levels must be attenuated to a level below –85 dBm before the diplexer in order to avoid desensing the B3 and/or B7 primary/diversity receivers[7].

Understanding Switch Configurations As shown below, the B8 harmonic levels must be attenuated to a level below –85 dBm before the diplexer[7]. Less than -85 dBm

Impact on data rate throughout the cell Impact on data rate throughout the cell In addition to CA, another technique designed to increase the data rate is termed “higher order modulation”. QPSK, 16-QAM, 64-QAM, and 256-QAM(to be released)[7]. This concept of diversity can be further applied to four antennas for yet another doubling of SNR (or 3 dB more increase) for the same data stream, thereby improving data rates[7]. This concept is called “MIMO”(Multi-input Multi-output).

Impact on data rate throughout the cell Impact on data rate throughout the cell For DL data rate, the relationship among modulation order, aggregated bandwidth, and MIMO[7].

Solving Downlink CA Challenges With downlink CA, the phone receives on two or more bands. The simultaneous reception on multiple bands creates a higher probability of interference. The interference challenges are increased by the fact that many smartphones now use multiple antennas. The challenge is to ensure cross-isolation and in-band isolation on both the primary and diversity Rx chains [3, 4-6].

Addressing Uplink CA Challenges Increasing uplink performance is particularly important for TDD-LTE because each band’s uplink data rates are limited by the fact that the same frequencies are used for uplink and downlink, with most capacity allocated to downlink[4]. Because intra-band CA involves the transmission of wideband signals with high peak-to-average ratios, it will require PAs with very high linearity. Envelope trackers will also need wider bandwidth capability to support these signals[4].

Addressing Uplink CA Challenges With inter-band uplink CA, interaction between the signals transmitted on different bands can create intermodulation frequencies that falls into Rx bands or auxiliary bands used for other purposes such as Global Positioning System (GPS).Intermodulation products can also be created in intra-band uplink CA via non- contiguous resource blocks[3,4].

Multiplexer Increasing the number of filters connected to the same antenna node leads to increased insertion loss in each filter passband. So the quadplexer using FBAR technology, like AVAGO ACFM-7107, is a good choice because FBAR is known for low loss resonators[8].

Multiplexer As shown in previous page, the nominal values for L and C shown there should be selected to match the quadplexer ANT port to 50 ohms. Otherwise, the in band isolation and cross band isolation may NOT be expected, thereby aggravating sensitivity. In general, the in band and cross band isolation should be at least 60 dB. The L and C matching components should be located in close proximity to the quadplexer. And the inductor should be of the high Q type. Wire-wound type has higher Q value than multi-layer type.

Multiplexer The recommended PCB Layout with ACFM-7106 and Ant Matching Components is as shown below:

Reference [1] Enabling Carrier Aggregation for dummies, Qorvo [2] LTE Carrier Aggregation Technology Development and Deployment Worldwide [3] ABCs of Carrier Aggregation [4] Carrier Aggregation: Implications for Mobile-Device RF Front-Ends [5] The Easy Way to a 1 Gbps RF Front-End on Smartphones, Qorvo [6] DL/UL Acceleration Technologies [7] LTE-Advanced Pro RF Front-End Implementations to Meet Emerging Carrier Aggregation and DL MIMO Requirements, IEEE [8] Multiplexers in Mobile Handsets with LTE-Advanced Carrier Aggregation, IEEE [9] RF front-end solutions for mobile applications selection guide, Infineon