Technical Article

Addressing RF Communication Challenges With GaN-on-SiC Power Amplifiers

January 24, 2024 by Baljit Chandhoke

This article examines the communication challenges of RF applications like 5G, satellite communications, aerospace, and defense and how GaN-on-SiC power amplifiers can help.

This article is published by EEPower as part of an exclusive digital content partnership with Bodo’s Power Systems.

RF systems need power amplifiers (PAs) to deliver linear, efficient, high-output power. As systems move to higher-order modulation schemes such as 64/128/256 Quadrature Amplitude Modulation (QAM), they must deliver high linearity and efficiency in denser environments with stringent peak-to-average power ratios (PAPR). A new generation of Gallium Nitride (GaN) on Silicon Carbide (SiC) Monolithic Microwave Integrated Circuits (MMIC) PAs offers a solution to these challenges with the highest power density to generate high linear output power with high efficiency.

 

Figure 1. Applications of millimeter-wave 5G. Image used courtesy of Bodo’s Power Systems [PDF]

 

RF Power Amplifier Opportunities and Challenges

The biggest growth opportunities and challenges for RF power amplifiers are in satellite communications and emerging 5G communications solutions. NASA has enabled private-sector companies to launch thousands of low-Earth-orbit (LEO) satellites circling the Earth, delivering broadband Internet access, navigation, maritime surveillance, remote sensing, and other services. These RF applications consistently seek size, weight, power, and cost (SWaP-C) benefits. Large dish antennas are being replaced with phased array antennas for satellite communication that require smaller size components for integration and lower weight components. High RF power, which is linear with high P1dB and IP3, reduces distortion and is efficient with high PAE to minimize power consumption, which is essential for these RF applications.

 

Millimeter-Wave 5G Communications

New generations of millimeter-wave 5G communication solutions, by their speed, ultra-wide bandwidth, and low latency for broadband communication, are substantially increasing how much information can be shared in support of real-time decision-making and other military applications. 5G systems operating in lower frequency bands (sub 6 GHz) have been vulnerable to high-power jamming signals, but 5G millimeter-wave (24 GHz and above) systems are bringing 5G networking to both on-battlefield and offbattlefield applications with the millimeter wave band that is not as vulnerable to high-power jamming signals. Examples include battlefield sensor networks for command-and-control data gathering and augmented reality displays that enhance situational awareness for pilots and infantry soldiers. 5G will also enable virtual reality solutions for remote vehicle operation in air, land, and sea missions. Off the battlefield, 5G will enable a variety of smart warehouse, telemedicine, and troop transportation applications.

5G mmWave Frequency Bands

Different countries have different bands for 5G mmWave. In the United States, 28 GHz was the first 5G mmWave band deployed, followed by 39 GHz. China is deploying 5G mmWave in the 24.25 – 27.5 GHz and has lagged in adopting the 5G mmWave.

 

Figure 2. 5G mmWave frequency bands globally. Image used courtesy of Bodo’s Power Systems [PDF]

 

5G Network Architecture

The 5G network is composed of macro base stations and small cells. The macro base station is connected to the core network using mmWave backhaul or fiber optic links. Macro base stations can talk directly to the user equipment cell phones or the small cells, which speak to the user equipment mobile device providing the last mile connectivity. Picocells and femtocells provide network connectivity inside office buildings where the connection might be weak or have high user density.

Femtocells are typically user-installed to improve coverage areas within a small vicinity, such as a home office or a dead zone within a building. Femtocells are designed to support only a handful of users and can only handle a few simultaneous calls—they have a very low output power of up to 0.2 watts.

Picocells offer greater capacities and coverage areas, supporting up to 100 users over a range of up to 300 meters. Picocells are frequently deployed indoors to improve poor wireless and cellular coverage within a building, such as an office floor or retail space. Picocells can be deployed temporarily in anticipation of high traffic within a limited area, such as a sporting event, but are also installed as a permanent feature of mobile cellular networks in a heterogeneous network working in conjunction with Macro cells to provide uninterrupted coverage for end users. They have an output power of up to 2 watts.

Macro base stations cover a large area of> km and have an output power of up to > 100 watts.

 

Type Output Power Distance
Femto Cell 10 mW to 200 mW 10 m to 50 m
Pico Cell 200 mW to 2 W 50 m to 300 m
Macro Base Station 10 W to >100 W >1 km
Figure 3. 5G network architecture comprising small cells and macro base station. Image used courtesy of Bodo’s Power Systems [PDF]

 

Radar Communications

Radar systems operate in the 1 gigahertz (GHz) to 2 GHz L band for applications including “identify friend or foe,” distance-measuring equipment, and tracking and surveillance. S-band (2 GHz to 4 GHz) is used for selective response Mode S applications and weather radar systems. X Band (8 GHz to 12 GHz) is used for weather and aircraft radar, while C Band (4 GHz to 8 GHz) is used for 5G and other sub-7 GHz communications applications. 5G mmWave provides the highest bandwidths and data rates, operating in 24 GHz and higher frequency bands. Satellite communications for LEO and geosynchronous communication operate in the K band, spanning 12 GHz to 40 GHz.

 

Figure 4. Marine Radar communication uses frequencies in the S-band, L-band, C-band, and X-band up to Ku/Ka-band. Image used courtesy of Bodo’s Power Systems [PDF]

 

RF Beamforming

Different types of phased array beamforming architectures used in these RF applications are:

  • Analog 
  • Digital 
  • Hybrid 

 

Analog Beamforming

For any phased array, the ideal separation between elements is wavelength lambda by 2.

Figure 5 shows analog beamforming. There are four phased array elements separated by wavelength lambda by 2. For a 30 GHz signal, there will be a 5 mm separation between phased array elements. In analog beam forming, the phase shifter does the beam forming by changing phase to do constructive interference for receiving and transmitting the signal by focusing the energy from the beam in a particular direction. This is all done at RF frequency; hence, it is most sensitive to interconnect losses. Then, the signal from the phase shifter goes to the power combiner/splitter, followed by the down converter and ADC/DAC to the baseband. In this case, only one digital front end exists for N-phased array elements. As seen in Figure 5, there is only one digital front end comprising ADC/DAC for four phased array elements. The benefit of this architecture is the smallest number of components and lowest power dissipation. However, as the phase shifting is done in RF bands, this beamforming architecture is most sensitive to interconnect losses and complexity in phase shifting.

 

Figure 5. Block diagram of analog beamforming with four-phased array elements. Image used courtesy of Bodo’s Power Systems [PDF]

 

Digital Beamforming

Digital beamforming has traditional up-down conversion to the baseband band frequency, and digital phase shifting is done. This architecture provides more precision as digital beamforming is done in the baseband. However, there is ADC/DAC for each phased array element, resulting in many components and high-power dissipation. In this case, for N phased array elements, there are N digital front ends. Figure 6 shows four digital front ends comprise ADC/DACs for four phased array elements.

 

Figure 6. Block diagram of digital beamforming with four phased array elements. Image used courtesy of Bodo’s Power Systems [PDF]

 

Hybrid Beamforming

Hybrid beamforming combining digital and analog beamforming is optimal for larger phased arrays to get the efficiency of analog beamforming with fewer elements, power dissipation, and precision of digital beamforming. Figure 7 shows two digital front ends comprise ADC/DAC for four phased array elements. Compared with analog beamforming, there was only a single digital front-end ADC/DAC; with digital beamforming, there were four digital front-end ADC/DACs.

 

Figure 7. Block diagram of hybrid beamforming with four phased array elements. Image used courtesy of Bodo’s Power Systems [PDF]

 

RF Signal Chain

Figure 8 shows the RF signal chain block diagram. At the receiver, the RF signal comes in through the antenna, goes through a limiter diode, followed by a switch, and the desired RF frequency is selected through the saw filters. The desired signal is then amplified through the low noise amplifier with an extremely low noise figure to minimize degradation in the signal-to-noise ratio of the received signal. Then, it is down-converted using a mixer. The local oscillator (LO) signal is generated using discrete PLL components comprising of a phase frequency detector and pre-scaler to provide the LO frequency to the mixer to down-convert the signal to an intermediate frequency (IF), followed by a conversion from IF to baseband for signal processing.

 

Figure 8. RF signal chain block diagram. Image used courtesy of Bodo’s Power Systems [PDF]

 

At the transmitter, the base-band signal is upconverted to IF and then to the desired RF frequency. The RF signal is amplified using a power amplifier to transmit the signal.

 

RF Figure of Merit

The table demonstrates the RF Figure of Merit and the benefits of components used in the RF block diagram.

 

RF Figure of Merit

Product Type Key Parameter Key Benefit
LNA Noise Figure (dB) Improved Range/Signal Sensitivity
PA OIP3 (dBm) & P1dB (dBm) PAE (%) Linear Efficient Power – Low Distortion
Prescale Phase Noise (dBc) @ kHz offset Low Noise Floor – More Range
Wideband Switches Low Loss (dB) / High Isolation (dB) Low Harmonics in System

 

Power Amplifiers Requirements

Power amplifiers play a key role as the transmitter in RF applications. One of the biggest PA requirements is that it can operate in its linear region to minimize RF distortion. Satellite communications systems that use higher-order modulation schemes such as 64/128/256 Quadrature Amplitude Modulation (QAM) are extremely sensitive to non-linear behavior. Another challenge is achieving a satisfactory peak-to-average power ratio (PAPR)—the ratio of the highest power the PA will produce to its average power. PAPR determines how much data can be sent and is proportional to the average power. At the same time, the size of the PA needed for a given format depends on the peak power. 5G mmWave effective isotropic radiated power (EIRP) requirements mandated by FCC include 43 dBm EIRP transmit power for the mobile handsets and base station transportable power of 55 dBm EIRP. These and other conflicting challenges can be met with GaN-on-SiC power amplifiers for satellite communication, 5G, aerospace, and defense applications.

 

GaN-on-SiC Power Amplifiers

GaN-on-SiC has the highest power density to generate high linear output power with high efficiency. GaN-on-SiC power amplifiers can operate at high frequencies in the Ka and Ku bands from 12 GHz to 40 GHz for satellite communication and 5G and have broad bandwidths, high gain, and better thermal properties, meeting the requirements of RF applications. Microchip provides RF solutions using GaN-on-SiC technology, meeting the SWaP-C requirement for components. ICP2840 is a flagship device that operates in 27.5–31 GHz, providing continuous wave (CW) output power of 9 watts and pulsed output power of 10 watts with a gain of 22 dB and power added efficiency of 22%.

 

Figure 9. ICP2840 linear PAE across frequency and output power levels. Image used courtesy of Bodo’s Power Systems [PDF]

 

Figure 10. ICP2840 linear gain across frequency and output power levels. Image used courtesy of Bodo’s Power Systems [PDF]

 

Microchip K Band Power Amplifiers

ICP2840 generates 9W continuous wave output power in the Ka-band from 27.5–31 GHz for uplink frequency for satellite communication and 28 GHz 5G frequency band. 

ICP2637 has a wide bandwidth from 23–30 GHz, generates 5 watts of CW output power, and is offered in a QFN package and die form. 

ICP1445 generates 35 watts of pulsed output power in the 13–15.5 GHz frequency Band. 

ICP1543 operates in the Ku band at 12 to 18 GHz, generating 20 watts of CW output power.

 

Figure 11. Microchip Technology’s Ku Ka-band GaN-on-SiC MMIC power amplifiers include ICP2840, which generates 9 W of continuous wave output power in the Ka-band from 27.5 – 31 GHz for uplink. Image used courtesy of Bodo’s Power Systems [PDF]

 

These PAs have high gain and power-added efficiency using GaN-on-SiC technology and meet the Ku/Ka band requirements for 5G, satellite communication, aerospace, and defense applications. GaN-on-SiC, with its highest power density, provides the optimal power amplifier solutions for these applications.