FEATURE WIRELESS TECHNOLOGY
New high-power switches in silicon technology help simplify RF front- end design for the new era of 5G
Bilge Bayrakci, marketing and product manager for RF & MW control products at Analog Devices, Inc. explores how the latest high-power silicon switches are offering considerable savings on bias power & external components in massive-MIMO RF front-end design
M
ultiple-Input-Multiple-Output (MIMO) transceiver architectures
are widely used in the design of high- power RF wireless communication systems. As a step into the 5G era, Massive-MIMO system covering cellular bands are now being deployed in urban areas to meet the emerging demand for high data throughput and a new variety of services. In essence, availability of highly integrated single-chip baseband transceiver solutions, such as ADI’s new ADRV9008/9 family of products, make this achievement possible. Similar integration towards lower power consumption for thermal management and smaller size for cost, is still needed at the RF front-end section of these systems, in order to accommodate more MIMO channels. MIMO architectures allow the RF power
requirements on building blocks such as amplifiers and switches to be relaxed. However, as the number of parallel transceiver channels increase the complexity of the peripheral circuits and power consumption scales accordingly. ADI’s new high-power switches in Silicon technology are designed to simplify the RF front-end designs by eliminating the need for peripheral circuits and reducing power consumption to negligible levels. ADI’s new high-power switches in Silicon offer RF designers and system architects the flexibility to increase their system complexity without RF front-ends becoming a bottleneck in their designs. In Time-Division-Duplex (TDD) systems, there is a switch function incorporated at the antenna interface to isolate and protect the receiver input from transmitted signal power. This switch function can either be used directly at the antenna interface in relatively lower power systems as shown in Figure 1 or used on the receive path as shown in Figure 2 for higher power applications to ensure proper termination to the duplexer. In both, having a shunt arm on the switch outputs will help to improve the isolation.
20 SEPTEMBER 2018 | ELECTRONICS Figure 1: Antenna switch
Figure 2: LNA protection switch
components or interface circuits. In Figure 4, internal circuit architecture is shown. A FET-based circuit operates on low bias currents and low supply voltages, bringing down the power consumption to negligible levels and helping the thermal management at the system level. Besides the ease of use, the device architecture yields better isolation as more shunt arms are incorporated on the RF signal paths. ADI’s high power silicon switches can handle up to RF peak power of 80 Watts that is enough to cover with margin the peak-to-average power ratio requirements for Massive-MIMO systems. ADI’s family of high-power silicon switches are optimised for different power levels and various package options. These devices inherit the intrinsic advantages of Silicon technology and yield better ESD robustness and part-to-part variation compared to its alternative solutions.
PIN diode-based switches have been prefered solutions with their low insertion-loss characteristics and high- power handling capabilities. However, their need for high bias voltages to reverse bias for isolation and their need for high current to foward bias for low insertion loss, are the short comings in the design of Massive-MIMO systems. In Figure 3, a typical application circuit is shown for a PIN diode-based switch and its peripherals. Three discrete PIN diodes are biased through their bias-tee circuits and are controlled through a high- voltage interface circuit. ADI’s new high-power silicon
switches are better suited to Massive-MIMO designs. They run on single 5V supply with less than 1mA bias current and do not need external
Figure 3: PIN diode switch
Figure 4: Silicon switch
THE FUTURE IS MIMO Massive-MIMO systems will continue to evolve and there will be further need for even higher levels of integration. ADI’s new high-power silicon switch technology is well suited for Multi-Chip- Module (MCM) designs to integrate with LNAs to offer a complete single-chip solution for TDD receiver front ends. ADI will also scale new designs towards
Figure 5:
ADI’s high-power silicon switches
higher frequencies and will lead similar solutions for Millimetre-Wave 5G systems. Circuit designers and system architects will also benefit from the advantages of the company’s new silicon switches in other applications such as phased array systems, as ADI expands its product portfolio with high-power silicon switches towards X-Band frequencies and higher commonly used frequency bands.
Analog Devices Ltd.
www.analog.com 01628 477 066
e:
uksales@linear.com / ELECTRONICS
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