Designer’s guide: 5G RF chips and modules

The increasing need for data and connectivity has driven the advancement of 5G technologies. The fifth-generation mobile network offers considerably higher speeds, reduced latency and the capacity to link many devices, extending the range of applications to several industries. Responsible for delivering and receiving data between devices and base stations, radio-frequency (RF) chips and modules are among the key components of 5G technology.

The added value of 5G technology

5G has improved the previous generation’s (4G’s) services, introducing three main capabilities.

Enhanced mobile broadband (eMBB)

Compared with 4G, eMBB achieves significantly higher data transfer rates and increased bandwidth. Up to 50 Mbits/s is available for the downlink in outdoor environments and 1 Gbit/s in indoor (5G LAN). The uplink is limited to half of these values. This translates into better performance for data-intensive applications, such as virtual reality and augmented reality.

5G employs the massive multiple-input, multiple-output (mMIMO) technique to increase data rates and improve spatial diversity. It uses a large number of antennas at both the base stations and user equipment.

Another technique used in 5G to improve communication is antenna diversity. Similar to MIMO, it uses multiple antennas but focuses more on signal reliability than data throughput.

Ultra-reliable low-latency communication (URLLC)

URLLC prioritizes the delivery of data with the highest reliability level, aiming to achieve success rates that exceed 99.999%. This is essential for mission-critical applications, such as autonomous vehicles or remote surgery, where even a single malfunction could result in severe repercussions.

URLLC aims to achieve extremely low latency, ideally below 1 ms. Real-time communication and control systems, such as industrial automation and remote control of vital infrastructure, as well as online gaming and video conferencing experience significant advantages from reduced latency.

Massive internet of things (mIoT)

Also known as massive machine-type communication (mMTC) in 5G terminology, mIoT is centered around establishing connections between a plethora of devices, potentially reaching into the billions, and integrating them into the network. These devices, typically sensors, smart meters, wearables or environmental monitoring systems, transmit relatively small amounts of data.

Efficient power usage is essential for mIoT devices. This involves using technologies engineered to maximize energy efficiency, ensuring that devices can operate for extended periods without needing frequent recharging.

Design challenges

Compared with the predecessor mobile technologies, 5G operates across a wider range of frequencies that can be divided into two frequency ranges:

• Sub-6-GHz bands (FR1) include all existing and new bands covering the 450-MHz to 6-GHz frequency range. These frequencies have been used for the initial rollout of 5G and currently handle the highest volume of 5G data transmission.
• Millimeter-wave (mmWave) bands (FR2) include the newly introduced 24.25- to 71-GHz frequency bands.

Although mmWave technology supports higher data transmission rates and larger bandwidth, it is hindered by increased signal attenuation and propagation difficulties. Designing for both frequency ranges requires addressing the following challenges:

• Signal attenuation: When it comes to signal loss, higher frequencies are more susceptible to the impacts of meteorological factors, such as precipitation, and vegetation. Due to this, the deployment of base stations must be more densely packed and RF components must be power-efficient.
• Beamforming: Beamforming focuses the transmit signal toward the intended receiver, enhancing signal strength and reducing interference. mmWave signals exhibit great directionality, necessitating the use of precise beamforming techniques to ensure robust connections. RF modules that have integrated beamforming capabilities are essential.
• Increased complexity: The increased bandwidth and higher frequencies of 5G present novel design obstacles, such as the need to handle more advanced modulation techniques and challenging signal-processing algorithms.
• Size and form factor: Compactness is one of the top priorities for modern electronics. Selecting RF components and modules with a small footprint is essential to achieve space-efficient designs. It should be noted that modern 5G devices require several antennas to cover all the available frequency ranges.
• Power consumption and thermal management: In mobile devices, such as smartphones, battery life is a critical resource. Selecting energy-efficient RF components is essential for maximizing battery life and reducing overall system power consumption.

Higher operating frequencies in 5G can lead to increased heat generation. Effective thermal management strategies are necessary to ensure component reliability and optimal performance.

5G FWA

Currently, there is a growing trend in the use of 5G fixed wireless access (FWA) technology. FWA is a method of connecting to the internet that replaces the traditional physical connection from the junction box to the residence with a wireless radio link.

Some operators offer a 5G FWA service using a frequency within the FR1 band, which is used by compatible 5G mobile devices (e.g., 3.5 GHz). Other operators, on the other hand, choose to operate in the FR2 frequency band, which is over 24.25 GHz (mmWave).

RF chipmakers are developing modules specifically designed for FWA applications. One example is Sivers Semiconductors AB’s BFM02803 RF module, which is optimized to seamlessly connect with baseband modems.

This RF module offers advanced features and operates throughout the 5G FR2 mmWave bands, spanning from 24.25 GHz to 29.5 GHz. The new module (Figure 1) incorporates 32 dual-polarized antenna elements that provide 2D beam-steering capabilities, allowing for adjustment in both azimuth and elevation.

RF chips and modules in 5G design

Several types of RF chips and modules play a critical role in enabling 5G functionality. Understanding their purpose and capabilities is essential for effective design.

Power amplifiers (PAs)

PAs enhance the transmit signal to ensure sufficient range and coverage. Efficient power amplifiers with wide bandwidth capabilities are necessary for 5G to manage a range of frequencies and complex modulation schemes.

Conventional PAs demonstrate non-linear characteristics, resulting in signal distortion and spectral regrowth, where the signal extends into neighboring frequencies. This becomes more critical in 5G applications due to the narrower bandwidth available.

Techniques such as Doherty PAs and envelope tracking (ET) are used to enhance the linearity of the PA and minimize distortion and spectral regrowth. Doherty PAs employ a dual-stage configuration consisting of a primary amplifier, which efficiently processes the majority of the signal, and a secondary amplifier that activates during signal peaks, enhancing the overall efficiency.

ET is a technique that adjusts the power supply voltage of the PA in real time, according to the signal envelope. This process optimizes efficiency and minimizes heat emissions.

Low-noise amplifiers (LNAs)

LNAs amplify weak received signals before processing. In 5G, LNAs with a high gain and low noise figure (a critical parameter that determines the minimum detectable signal level) are necessary to overcome signal attenuation, especially in mmWave bands where signals are weaker. In some cases, designers may cascade multiple LNAs with varying gain stages to achieve the desired noise figure and overall gain for the system.

Finwave Semiconductor Inc., a spinoff of MIT, has developed a semiconductor technology, the 3DGaN FinFET, that aims to enhance linearity and power density in 5G PAs and LNAs. Built on 8-inch GaN-on-Si wafers using standard silicon foundry tools, this technology achieves more than 10-dB-higher linearity compared with conventional technologies. Finwave’s patented technology exhibits excellent linearity, where the gain (G_M) remains constant over a wide V_GS range.

RF filters

These devices selectively allow desired frequencies to pass through while effectively blocking out any unwanted noise and interference. For optimal performance, it is critical to have filters that offer excellent selectivity and can effectively handle wider bandwidths. These filters play a vital role in reducing any potential interference from different bands.

Surface acoustic wave (SAW) filters

These filters are known for their high selectivity and are commonly used in sub-6-GHz bands. Bulk acoustic wave (BAW) filters are preferred at higher frequencies because of their better miniaturization than SAW filters. In mmWave bands, RF cavity filters offer excellent selectivity but with increased complexity and cost.

Switches and multiplexers

These components route and manage RF signals within the system. For 5G, high-speed switches and multiplexers are needed to handle the rapid data transfer rates and enable functionalities such as antenna diversity.

RF front-end modules (RFFEs)

RFFEs integrate RF components such as PAs, LNAs, filters and switches into a single, compact package. They simplify design by offering pre-tested and characterized solutions optimized for specific frequency bands.

RF transceivers

By combining transmitter and receiver functions into a single device, RF transceivers enable effective communication between the user equipment and the network.

To meet the demanding requirements of 5G, there has been a transition from specific frequency-band designs to single-chip transceivers that optimize the entire radio solution rather than focusing on individual components or interfaces.

Integrating RF and digital functions, these devices enhance the performance of 5G radio systems, reduce the number of external components (such as FPGAs) and optimize power consumption.

One example is Analog Devices Inc.’s ADRV9040 system-on-chip (SoC) RF transceiver that operates from 650 MHz to 6 GHz. This device meets the high performance, low power consumption and reduced size required by cellular infrastructure applications, including small-cell base station radios, macro 3G/4G/5G systems and mMIMO base stations.

The ADRV9040 RadioVerse SoC 8T8R integrated transceiver supports 400-MHz bandwidth and offers advanced digital front-end functionality, including ADI’s Gen 5 digital predistortion engine with crest factor reduction and integrated carrier digital up and down converters. Together, this functionality can significantly reduce size or eliminate the need for a system FPGA.

The ADRV9040 (Figure 2) also integrates discontinuous transmission (DTx), a proprietary feature that, when enabled, can turn the RF front end on and off during periods of null transmission. In lab trials with Vodafone, this feature can reduce radio unit energy consumption by more than 35%, ADI said.