Issue link: https://resources.mouser.com/i/1313800
Figure 5: Differences in coverage and capacity are distinct between 5G mmWave and sub-6GHz. Sub-6GHz massive MIMO will solve interference problems by using a large number of antennas at the base station and will enable base stations to serve large numbers of users in urban areas. Massive MIMO also boosts peak, average, and cell-edge throughput, maximizing cost efficiency by providing the optimal balance between user coverage and capacity. These technology advances do not come without system design challenges. Sub-6GHz massive-MIMO beamforming technology will drive demand for small, highly efficient, cost-effective power amplifiers (PAs) that can be used in massive-MIMO arrays. Also, because the 5G modulation schemes are becoming more complex (i.e., 256 QAM), wireless infrastructure PAs will need to be very efficient under the deep output-power back-off conditions (up to 8dB or more) that will be required to achieve the necessary linearity. Making 5G Massive-MIMO Sub-6GHz a Reality Using GaN High output power, linearity, and power-consumption requirements are pushing base-station and network OEMs to switch from using LDMOS technology for PAs to gallium nitride (GaN). GaN offers numerous advantages for 5G sub- 6GHz massive-MIMO base-station applications: • GaN performs well at 3.5GHz frequencies and above, while LDMOS is challenged at these high frequencies. • GaN has high breakdown voltage, high current density, high transition frequency, low on-state resistance, and low parasitic capacitance. These properties translate into high output power, wide bandwidth, and high efficiency. • GaN in a Doherty PA configuration attains average efficiencies of 50% to 60% with 100W output power, significantly reducing transmit power consumption. • The high-power density of GaN PAs enables small form factors that require less printed-circuit-board (PCB) space. • Using GaN in a Doherty PA configuration allows for the use of quad-flat no-leads (QFN) plastic packages rather than the expensive ceramic packages. • GaN's efficiency at high frequency and over wide bandwidths means that massive-MIMO systems can be more compact. GaN reliably runs at higher operating temperatures, meaning it can use a smaller heat sink. This enables a more compact form factor. | 25 |