RF Front End in the 5G Era

The RF front end is the section between the antenna and the IF (or baseband) circuit in a communication system. In this section, the signal is transmitted in RF form. For wireless receivers, the RF front end usually includes amplifiers, filters, converters, and some RF connection and matching circuits.

What is an RF device?

RF devices are the core of wireless connectivity and are essential wherever wireless connectivity is needed. The number of wireless connections worldwide will grow exponentially in the future, driven by IoT applications.

RF devices are the basic components of wireless communication devices and play two important roles in wireless communication, i.e., they play the role of converting binary signals into high-frequency wireless electromagnetic signals in the process of transmitting signals and converting received electromagnetic signals into binary digital signals in the process of receiving signals.

Regardless of what kind of communication protocol, the communication frequency used is high or low, with the RF device module being the basic component necessary for the system. Whether using 13.56Mhz signal as the transmission carrier NFC system; or using 900/1800Mhz signal as the transmission carrier GSM communication system; or using 24Ghz and 77Ghz electromagnetic wave signal as the transmission carrier unmanned millimeter-wave radar, all need to be equipped with RF device module.

As an indispensable foundation of wireless communication, the technological innovation of RF devices is one of the core engines to drive wireless connectivity forward. In an environment of massive growth in connected devices, the RF device industry is the fastest growing and most certain directional asset for the future.

Important components of RF front end

(1) PA ( Power Amplifier): achieves the transmit channel RF signal amplification

(2) RF filter: retains the signal in a specific channel, while the signal outside a specific frequency band will be filtered out

(3) Duplexers: transmit and receive the signal isolation, to ensure that the reception and transmission in the case of a common antenna can work properly

(4) LNA (Low Noise Amplifier): achieves the amplification of the RF signal of the receiving channel

(5) RF switch: achieves the switch between RF signal reception and transmission. Switching between different frequency bands.

(6) Antenna Tuners: An impedance matching network connecting the transmitting system to the antenna, so that the antenna radiates the maximum power at the applied frequency.

The composition of the RF front end

5G makes RF front end design complexity order of magnitude higher

The RF front end is one of the core devices in a smartphone and consists of four main modules: a power amplifier (PA), a switch, a filter, and a low-noise amplifier (LNA).

The birth of each generation of communication mobile technology triggers significant changes in the related industries. 5G's high speed, large connection, and low latency characteristics bring huge challenges to RF front end design, and the complexity increases exponentially.

On the one hand, the RF front end has to act as the pioneer general of wireless receiving link, completing the work of antenna switch tuning, filtering, low noise signal amplification, and handing over the initial amplified signal to RF SoC for further frequency conversion and digital processing. On the other hand, the RF front end also assumes the role of ultimate guardian of the signal at the transmitting link end, realizing signal filtering and power amplification to ensure the signal transmitting quality.

Before the birth of 5G communications, most mainstream RF front ends used discrete device solutions. In order to achieve multi-band support, the number of filter devices, amplifiers, and switches kept increasing, plus peripheral matching circuitry and hundreds of components had to be accommodated between square inches. 5G era has come to integrate carrier aggregation, high-order modulation, Massive MIMO, and other technologies, which makes the design complexity of 5G RF front end multiply, bringing serious challenges to the cost, volume, and market competitiveness of the solution.

As an example, for each additional frequency band of a cell phone, about 2 additional filters (receive and transmit), 1 power amplifier, and 1 antenna switch are required. In addition to the significant increase in the number of frequency bands, the high-frequency bands of 5G make signal processing twice as difficult, and the system places higher demands on filter performance. For 5G, the demand for the number of filters may be as high as a hundred.

What are the technical enhancements in the 5G RF front end?

What is 5G?

5G is a technology that represents not just a cell phone, but more of a new way of production and new way of interaction.

The cell phone, which is just one of the carriers, is one of the most closely connected media in the eMBB scenario. Later, as mMTC and uRLLC scenarios unfold, the battlefield of 5G will not only be limited to this but a larger jungle will be laid out.

The opportunities contained therein will emerge gradually with the development of the timeline in general. What we need to do now is to plan ahead and fully discover the five times and ten times stock opportunities.

In the early era of 5G, the wireless communication module of the terminal equipment is the most first.

And wireless communication module includes four parts: antenna, RF front end module, RF transceiver module, and baseband signal processor. Among them, RF front end and antenna are the fields that belong to the volume and price are rising and the demand is expanding dramatically.

The opening of the 5G era has made network base stations and user devices (e.g., cell phones) increasingly slim and compact, and the energy consumption is becoming lower. In order to fit into small-sized devices, the printed circuit boards (PCBs) used in many RF applications are also being reduced in size. A typical RF front end consists of switches, filters, amplifiers, and tuning components. In 5G applications such as cell phones, small cells, antenna array systems, and Wi-Fi, the RF front end is becoming a complex, highly integrated system envelope.

What are the technological enhancements to the RF front end module as a core component?

Gallium Nitride Technology

Gallium Nitride (GaN) is a binary III/V group bandgap semiconductor ideally suited for high power, high-temperature tolerant transistors.

Gallium Nitride Technology

Some of the important attributes of GaN technology.

Reliability and sturdiness: GaN is more power-efficient and therefore has a lower heat output. Using GaN eliminates the need for these costly heat dissipation solutions.

Low current consumption: Gallium nitride reduces operating costs and generates less heat. In addition, the low current helps reduce system power consumption and lower power requirements.

Power capability: GaN devices offer higher output power than other semiconductor technologies.

Frequency bandwidth: GaN has high impedance and low gate capacitance, enabling greater operating bandwidth and higher data transfer speeds.

Integration: The need for smaller solutions for 5G is driving suppliers to replace discrete RF front ends, which are large scale and contain multiple technologies, with monolithic, fully integrated solutions.

Body acoustic wave filter technology

Surface acoustic wave filters and bulk acoustic wave filters are dominating the mobile device filter market with their small footprint, high performance, and affordability.

Body acoustic wave filters are best suited for the 1 GHz to 6 GHz band, and surface acoustic wave filters are best suited for the sub-1 GHz band.

For smartphone designers, the introduction of 5G presents another challenge for battery life and motherboard space.

Bulk Acoustic Wave Filter Technology

Not surprisingly, the number of filters installed in a phone increases dramatically from 4G to 5G, with carrier aggregation being a major contributor to the increase in the number of filters.

One advantage of bulk acoustic wave technology is heat dissipation, as shown in the figure.

Bulk acoustic wave technology for heat dissipation

RF Technology, Packaging, and Design

RF front ends consist of multiple semiconductor technology devices. The many 5G applications require a wide variety of processing technologies, design techniques, integration approaches, and packaging methods to meet the needs of each unique use case.

For the sub-7 GHz band of 5G, the corresponding RF front end solutions require innovative packaging approaches, such as increased compactness of component arrangements; shorter lead lengths between components to minimize loss; double-sided mounting; zoned shielding; and the use of higher quality surface mount technology components.

All 5G use cases require RF front end technology. The choice of RF semiconductor technology varies depending on RF functionality, frequency band, power level, and other performance requirements. As shown in Figure, each RF function and application corresponds to multiple semiconductor technologies.