Page 19 - EngineerIt August 2021

ICT 5G

One potential PoE solution is outlined in Figure 11. This
solution includes the LT4321 bridge controller that allows MOS
transistors to be used as ideal diodes instead of rectifiers, the
advantage of which is much improved efficiency. This is followed
by the LT4295, an 802.3bt compliant PD device. This can then be
followed by appropriate local regulators to fulfill the requirements
shown in the previous table, providing up to 90+ W as required.
Beyond the PoE conversion devices, many other devices are
available in support of a small cell reference design. These include
cornerstone devices like the ADP5054 family, which is specifically
designed to power ADI transceivers as well as many other buck Figure 14: 5G prototype platform with re-bandable RF front end.
converters and lower noise LDO regulators, as shown in Figure 12.
is low for many small cell applications, the circulator may be replaced
Options by a simple TR switch. Finally, if only local area performance is
One of the great things about this radio architecture is the flexibility required, the dual stage LNA may be replaced by a simple single
that it affords in terms of meeting a range of market requirements. stage LNA. The result is a lower cost option still providing good radio
This architecture is optimised for a range of applications including performance. An example of this is shown in Figure 13. Many other
both FDD and TDD. It is equally capable of performance in low, permutations are available to suit a wide range of possibilities across
mid and high band and is well suited for small cell through massive a wide range of frequency and power options.
MIMO platforms. Many different trade-offs can be made in both the
transmitter and receiver circuits to optimise for cost, size, weight Conclusion
and power. While this introduction focused on higher performance The 5G technology devices reviewed here are available for
and integration, it is possible to make some simple trade-offs in communications applications and enable low-cost implementations
favour of cost with slightly different selections. suitable for 5G development, especially those implementing O-RAN
For example, some low power PAs do not require a drive O-RU solutions. These include devices from the RadioVerse family
amplifier and therefore may not be required. Because the RF power as well as RF amplifiers, clock recovery/synchronisation, and
power over ethernet/point of load regulation. Together this highly
integrated set of devices is ready for implementation of 5G small
cell, macrocell, microcell, and massive MIMO applications.
When combined with a suitable PHY and software provided
in an FPGA, eASIC, or ASIC, a complete O-RU solution may be
developed, as shown in Figure 14. This solution was developed
with partners at Intel , Comcores, and Whizz Systems. These
®
solutions meet not only the required RF characteristics but also the
cost and power budgets required to enable deployment of low cost,
high performance O-RAN platforms. n
Sources
1. ftp://ftp.3gpp.org/specs/latest/Rel-15/38_series/
Figure 11: A PoE isolated small cell power solution. 2. O-RAN Alliance.
3. “O-RAN: Towards an Open and Smart RAN.” O-RAN Alliance,
October 2018.
4. Brad Brannon. “Where Zero-IF Wins: 50% Smaller PCB
Footprint at 1/3 the Cost.” Analog Dialogue, Vol. 50, No. 3,
September 2016.
5. Specifications. O-RAN Alliance.

About the author
Brad Brannon has worked at ADI for 37 years following his
Figure 12: A typical power tree for small cell applications. graduation from North Carolina State University. At ADI he has
held positions in design, test, applications and system engineering.
Currently Brad is developing reference designs for O-RAN and
supporting those customers. He has authored several articles and
application notes on topics that span clocking data converters,
designing radios and testing ADCs. He can be reached at brad.
brannon@analog.com.

Analog Devices (www.analog.com) is represented in South Africa
by Altron Arrow. For more information contact Conrad Coetzee at
Figure 13: Alternate transceiver signal chain. ccoetzee@arrow.altech.co.za

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