Protecting 5G Macro Base Station Amplifiers and Antennas From Electrical Hazards
This article dives into protecting tower-mounted amplifiers and advanced antenna systems of 5G macro base stations from electrical hazards.
The next generation of cellular communication, 5G technology, offers increased speed, greater consistency, and lower latency.
This fifth generation of mobile networking is expected to have the capacity to allow communication among one million devices/km2, which is a factor of 10 greater than the 4G technology.
The advances of 5G could enhance consumer experiences and facilitate emerging technologies such as:
- Automated vehicles
- Smart homes/cities
- Automated factories
- Advancement in agricultural technology
While these are just a few areas where 5G will have an impact, it all is highly dependent on the data centers and supporting communications base stations.
Reliability of the infrastructure equipment is critical for the successful adoption of 5G networks.
Electronics design engineers need to protect their 5G infrastructure designs by developing circuits that protect against five sources of electrical hazards that affect the reliability and the lifetime of their equipment.
These hazard sources are:
- Lightning-induced surges
- Transient voltage surges resulting from large inductive load switching caused by motors
- Electrostatic discharge (ESD)
- Current overloads
- Short circuits
This article provides a detailed description of a macro base station and offers recommendations for protecting the base station circuitry, namely the tower-mounted amplifier and the advanced antenna systems from sources of electrical hazards.
The Macro Base Station
The base station connects the core network to the individual mobile phones and other wireless devices such as watches, tablets, and IoT devices via both transmission and reception. Baseband information is modulated and transmitted to mobile devices; and, mobile device transmissions are received, demodulated, and transmitted to the wireline infrastructure.
Macro base stations are tall towers with heights ranging from 50 to 200 feet. They are usually visible structures and strategically located to maximize coverage in a geographic area.
The base station must connect to all wireless devices attempting to communicate with the base station in the coverage area it serves.
The 5G base stations contain advanced, active antenna systems containing multiple antennas in multiple input-multiple outputs (MIMO) technology configurations.
The advanced, active antennas provide higher transmission/reception capacity, faster data transmission rates, and more efficient delivery of RF power.
Figure 1 shows all the elements that make up a base station and the recommended protection, control and sensing components that protect and improve the efficiency of the base station circuits.
Figure 1. Macro base station with an advanced antenna array
Figure 2 shows a block diagram of the base station circuitry.
Figure 2. Macro base station block diagram
Protection Components Inside the Surge Protection Device
The surge protection device interfaces with the AC power line and is subject to transients inherent in the AC power line.
A surge suppression fuse on the input of the surge protection circuit is recommended. This type of fuse can withstand a lightning surge up to 200 kA based on transient surges defined in UL 1449 and IEC 61000-4-5. This fuse also acts to provide current limiting protection under short circuit conditions.
Following the surge suppression fuse, consider using a series combination of a metal oxide varistor (MOV) and a gas discharge tube (GDT) to absorb the lightning strike and other large transients arising from load changes that occur on the power line.
Place the MOV-GDT combination as close to the input as possible to minimize the transient propagation into the circuit.
Connect the MOV between Line and Neutral and connect the gas discharge device from neutral to ground.
Additionally, a high-power transient voltage suppressor (TVS) diode is an alternative to a MOV if the TVS diode’s maximum surge handling capacity is adequate for the AC power line feed. TVS diodes have faster response times and clamp transients at lower voltages.
Protecting the Tower-Mounted Amplifier
The tower-mounted amplifier is exposed to the outdoor environment and needs protection from lightning strikes and ESD.
This circuit should have a series fuse to protect against current overloads and a parallel TVS diode to absorb lightning or ESD transient strikes.
High-power TVS diodes can safely absorb current overloads as high as 10 kA. These components are available in surface-mount packages when space constraints are critical.
Protecting the Advanced Antenna System
The Advanced Antenna System (AAS), as shown in Figure 3, both receives and transmits information, audio communication, and data communication from and to the mobile wireless devices in the geographic cell.
Figure 3. Advanced Antenna System Block Diagram
Digital packets from the baseband unit are converted to analog data and upconverted for RF transmission. Received RF signals are down-converted and digitized for transmission to the baseband unit.
Power Input Circuit
The power input circuit provides the DC power for the other AAS circuits.
On the input stage, a fuse for overcurrent protection is recommended. For this DC circuit, a fast-acting fuse is a suitable choice. Surface mount fast-acting versions are available for space-saving applications.
Consider a MOV and a gas discharge tube in series to protect the front-end of the power input circuit from transients that have passed through the SPD and the power supply and backup battery circuit.
Since the power input feeds all the other circuits, consider protecting these circuits from transient and ESD protection with a TVS diode at the back-end of the power input circuit. A TVS diode has a lower clamping voltage than a MOV and enables the use of lower, voltage-rated (and lower cost) components in the downstream circuits.
Ethernet and RS-232 or RS-485 Communication Circuits
To protect the integrity of the communication ports, use transient protection with crowbar protection components.
If a Power-over-Ethernet (PoE) communication link is in use, consider a protection thyristor, such as the component shown in Figure 4, which protects two data lines from ESD strikes.
Figure 4. Two-line protection thyristor for protection of Power-over-Ethernet circuits. Figure 4a. Schematic of a two-line component with a protection thyristor tied to each line. Figure 4b. I-V curve of a protection thyristor
An alternative protection solution is using a TVS diode array and a gas discharge tube.
An example two-line TVS diode array is shown in Figure 5.
Figure 5. Two-line TVS diode array with a parallel Zener diode
This device employs a Zener diode for clamping a transient compared with the protection thyristor, which crowbars the transient. Look for versions of these components with low capacitance to minimize the impact on the quality of the data transmissions. If the protocol is PoE, include a fuse to protect the Ethernet circuit from an overload resulting from crossed lines connecting to the circuit.
For an RS-232 or an RS-485 interface, consider using a protection thyristor and a gas discharge tube combination for transient protection. For current overload and crossed-line protection, consider a resettable polymeric positive temperature coefficient fuse for increased design flexibility.
In Part 2 of this article series, we'll address the circuit protection design requirements for the 5G baseband processor unit, network controller, RF front-end power amplifier, and supporting power supply and battery backup system.
To learn more, download the Circuit Protection Products Selection Guide, courtesy of Littelfuse, Inc.
All images used courtesy of Littelfuse, Inc
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