An Innovative Approach to Base Station Design Using PAMs

Figure 1: FR1 and FR2 5G ecosystem.

• Massive MIMO is an extension of MIMO technology. It essentially uses the same frequency spectrum multiple times to increase capacity and coverage of the data transmitted. This allows for a more efficient use of spectrum. This move to mMIMO increases the number of channels from 4, to 16, 32, 64, 128 and higher, as shown in Figures 1 and 2. mMIMO technology helps by reducing signal problems, making connections faster, improving signal strength, cutting down on dropped calls, and allowing for better signal direction.
• The development of cellular base stations has evolved to meet consumer demands, moving towards advanced active array antenna designs. (See below Figure 2) This evolution is highlighted by mMIMO architectures, the 3 GHz C-band frequency, and the need for ultra-high capacity. With the introduction of 5G – Advanced in 3GPP Release 18, we will see implementations of 128 transmit/receive (128T/128R) and 256 transmit/receive (256T/256R) setups, offering unprecedented capacity in 5G-Advanced microwave networks. While mMIMO technology brings many advantages, it also requires PAs that are both highly efficient and linear to meet the demanding requirements of 5G base stations as well as driving the need to achieve this performance in an increasingly smaller footprint.

Figure 2: Evolution of cellular base stations.

• Active array antennas with beamforming can quickly steer beams and support multiple independent beams at once. They are low-profile, reliable, and have no mechanical parts. With many elements, they can effectively block interference and create precise radiation patterns. Beamforming is a big part of 5G base station design. It uses multiple antennas to control the direction of the signal wave form. It does this by appropriately weighing the magnitude and phase of the individual antenna signals in an array of multiple antennas. These 5G-Advanced antennas will operate in the microwave and mmWave frequency ranges. At higher frequency ranges, the signal wavelengths are very short, as shown in Figure 3 below, allowing many antennas to be placed in a small area.

Figure 3: mmWave lambda wavelength and spacing.

• Higher frequency operation reduces the lambda/2 (half-wavelength) spacing between the antenna array elements which requires a more compact and integrated RF front-end (RFFE) solution. See Figure 3 above.

PAMs Enable Compact and High Frequency 5G Base Stations

As someone interested in technology, you're probably wondering how current tech-solutions can fulfill the demands of 5G base station systems. While various technologies available today could work in a design, only the best technologies meet today's 5G standards and provide wireless companies with compact, efficient solutions. Let's introduce you to a cutting-edge solution designed to make building your base station system quicker, easier, and more reliable, all while addressing the 5G needs mentioned earlier.

Enter gallium nitride (GaN) power amplifier module (PAM) technology, an RF power device in a small, highly integrated package. PAMs, as shown in Figure 4, are the puzzle piece that efficiently and effectively completes the RF front-end.

Figure 4: Block diagram of PAM QPA and QPB (bias controller) products.

At a high level, let’s list some of the PAM advantages/design benefits:

• These integrated devices are optimized for mMIMO 5G base stations.
• They are optimized for 50 Ohm input and output impedances.
• Have a significantly smaller footprint than a discrete PA solution.
• Improves final system yields and decreases design time – in contrast to a discrete PA solution, which requires PA tuning and matching. The PAM solution can achieve optimum performance without the need for a PA or Doherty PA system-level PCB match.
• Allows for the inclusion of a factory-programmed integrated bias controller. This controller adjusts the gate bias over the operating temperature range, ensuring optimal performance of the module.
• These new devices have wide-bandwidth performance -- well suited for C-band and higher band wideband performance.
• With its improved efficiency and linearity, it carries those improvements into the base station systems.

A Deeper Dive on How PAMs Align to Market Needs

Qorvo’s GaN and PAM technologies were developed to meet the evolving needs of the wireless infrastructure market. Using GaN technology, Qorvo was able to provide a solution to meet market performance requirements and base station original equipment manufacturer (OEM) and cellular carrier desires. Let’s review how PAMs align to market needs in the below bullets.

• The development of 5G base station antenna design includes more RF front-end antennas and a broader frequency range. This change has led to lower overall system power levels but also added complexity. It has required the PA to be more efficient and linear. Advancements in GaN technology have made PAs both more linear and efficient. With Qorvo's GaN technology, PA and PAM line-up efficiencies can reach up to 48%, with error vector magnitudes (EVM) under 2% and adjacent channel leakage ratios (ACLR) of 50 dBc with the implementation of linearization techniques. These parameters reduce power consumption for carriers and OEMs, contributing to more environmentally friendly base station systems. Let’s dig deeper into each of these parameters and their influence on the 5G ecosystem.
• Improved efficiency – This translates to using less energy and producing less heat. As a result, system designers can create simpler, lighter designs without complex heat management. This leads to lower OPEX (operational expenditures), quicker development times and more reliable systems
• Improved linearity – As cellular frequency bands expand and bandwidths increase, it's crucial to design systems that transmit signals precisely within the required band without leaking into nearby bands. For instance, the cellular C-band is close to frequencies used by airlines. Better linearity in system design minimizes unwanted emissions.
• Improved EVM – Improving signal quality and the bit error rate enhances how accurately data is transmitted and received. EVM assesses this by measuring how much the actual signal points differ from their perfect positions on a constellation diagram. EVM is a key indicator of a digital radio system's performance. In RF systems, a high EVM, which means lower quality, can result from issues like thermal noise, phase noise, and the power amplifier's inconsistent response in both amplitude and phase.
• 5G-Advanced – For 5G-Advanced technology, smaller components are essential for fitting many RF front ends and antennas into compact spaces to meet high frequency requirements. Achieving smaller sizes in PA designs and the overall system is crucial. One effective strategy for reducing size in the semiconductor field is integration, and PAMs excel in this. (See Figure 5 below). PAMs combine multiple functions, including the controller, into a single unit while still meeting or exceeding the performance standards for 5G base station design. This not only leads to smaller, more efficient packages but also eliminates the need for separate matching components, as PAMs come with built-in 50-ohm input/output matching. This simplifies the system design and reduces costs.

Figure 5: Comparison between discrete PA and integrated PAM.

A Final Word

Today’s RF base station systems are becoming smaller, requiring wider RF bandwidth, increasing in frequency, using mMIMO and beamforming technology, and must be lighter, smaller, “greener” and more reliable. Meeting these needs does not always come easy, but just as the base station designs are advancing, so are the technologies used within them. The introduction of the PAM is one such advancement. These highly integrated devices make system design easy, while meeting all of today’s system-level requirements. Helping system design engineers get to market faster and with shorter design time cycles means OEMs meet their customer design and implementation initiatives.

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For more information on this and other Qorvo 5G and 6G base station design solutions please visit Qorvo.com or reach out to Technical Support.