As soon as 5G hits have been achieved, DC-DC converters may be the rescue of the RF energy amplifier

With the upcoming 5G rollout, the engineers were commissioned to redesign a large part of the cellular network infrastructure to support the high frequencies offered by 5G. One of the biggest challenges with this design is to minimize power consumption. Lower power consumption means longer battery life in phones and less money in base stations.

Breakdown of power consumption by components in RF systems. Image courtesy Mouser

As Timothy Hegarty of Texas Instruments points out, power amplifiers are the primary consumers of energy in both base stations and cellular devices. For this reason, the engineers have further developed this component in order to maximize its energy efficiency.

Interestingly, DC-DC conversion technologies can be key to optimizing the energy efficiency of RF power amplifiers. Flex Power Modules recognized this reality and recently partnered with OpenRAN and the O-RAN Alliance to expand the range of DC-DC converters for RF power amplifiers.

One of the fully regulated analog DC / DC converters of the Flex Power Module, the PKM4516AD. Image courtesy of Flex Power Modules

“We are leveraging our interaction with OpenRAN members to provide companies with a wide variety of DC-DC parts that are ideal for RFPA applications,” said James Zhang, APAC sales director for Flex Power Modules.

An overview of RF power amplifiers and their power efficiency can help us evaluate DC-DC converters as a solution, especially given 5G.

What is an RF power amplifier?

RF power amplifiers (RFPAs), in simple terms, are devices that convert a low-power, high-frequency signal to a high-power, high-frequency signal.

Block diagram showing where an RFPA works in sequence. Image courtesy of Analytical Graphics

These components are used in the transmitter section of an RF system because they are required to drive the antenna and transmit the signal.

Why are RF power amplifiers inherently inefficient?

Due to the fundamental laws of thermodynamics, it is physically impossible for electronic devices to achieve 100% energy efficiency. RF applications suffer from particularly poor energy efficiency due to the many obstacles in converting DC to RF power. These causes include signal path loss, high operating frequencies, and inherent defects in devices.

The gain compression is shown graphically. Image courtesy Keysight

In an RFPA, linearity is equally important for energy efficiency. Linearity is critical because the modulation schemes used in cellular communications produce amplitude modulated signals that have a non-constant amplitude envelope.

Unfortunately, this is a compromise with energy efficiency, as efficient PA operation occurs with gain compression (when amplifiers do not have a linear relationship between input and output power). Hence, for reasons of linearity, power amplifiers are forced to operate less efficiently.

Other causes of RFPA inefficiency and solutions

In the past, the power amplifier in a mobile radio device was fed directly from the device’s battery. In this way, it becomes a source of inefficiency because, as mentioned earlier, cellular modulation schemes result in signals not having constant amplitudes. Essentially, we are supplying an amplifier with a constant amount of power, even though the amount of power actually required varies.

Traditional PA operation leads to wasted energy. Image (modified) courtesy of Digi-Key

Engineers creatively developed techniques such as APT (Average Power Tracking) and ET (Envelope Tracking) to address this problem.

Energy savings through APT and ET compared to fixed voltage. Image courtesy Texas Instruments

Using these techniques, the power delivered to the amplifier is determined either by the average power of the signal or by the envelope of the signal.

How a DC-DC converter can help

A DC-DC converter can improve some of these power inefficiencies in RF power amplifiers. A DC-DC converter is required to provide real-time power tracking and dynamically adjust the DC supply voltage.

How a DC-DC converter can be used to save energy in RFPAs. Image (modified) courtesy of Digi-Key

For RF applications, a linear regulator seems to be the best choice for a transducer because it generates very little noise and there is no high frequency switching that could potentially interfere with the RF signal.

However, since performance is a major concern, linear regulators are not chosen because of their inefficiency. This has led companies to develop DC-DC converter modules that are specially optimized for RF power amplifiers.

With 5G, energy efficiency is the key

For 5G to be successful on a large scale, it has to be energy efficient. Energy efficiency saves costs in energy and cooling solutions. For these reasons, companies like Flex Power Modules are using O-RAN and OpenRAN to expand their presence in the RFPA market.

The continued development of RFPA-specific DC-DC converters will hopefully lead to scalable and affordable 5G solutions to support cellular and IoT applications.

If you are working with the cellular infrastructure for 5G, how did you factor energy efficiency into your design? Share your experience in the comments below.

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