“In the later deployment of 4G LTE cellular base stations, large-scale multiple-input, multiple-output (MIMO) radio technology is widely used, especially in dense urban areas, small cells effectively fill the gap in cellular coverage while improving data services speed. The success of this architecture clearly confirms its value. Because this architecture itself has the required spectrum efficiency and transmission reliability, it will become the preferred architecture for emerging 5G network radios.The challenge to make 5G a reality is that designers must significantly increase the number of transceiver channels that operate in multiple frequency bands at the same time, while at the same time integrating all the necessary hardware compression and integration with previous generation devices.
In the later deployment of 4G LTE cellular base stations, large-scale multiple-input, multiple-output (MIMO) radio technology is widely used, especially in dense urban areas, small cells effectively fill the gap in cellular coverage while improving data services speed. The success of this architecture clearly confirms its value. Because this architecture itself has the required spectrum efficiency and transmission reliability, it will become the preferred architecture for emerging 5G network radios. The challenge to make 5G a reality is that designers must significantly increase the number of transceiver channels that operate in multiple frequency bands at the same time, while compressing and integrating all the necessary hardware into the same size or smaller space as the previous generation of devices.
Doing this means:
u The more channels, the higher the RF power inside and outside the base station, which will exacerbate the problem of isolation between channels that do not interfere with each other.
u In order to maintain reliability under high-power signals, receiver front-end components must improve dynamic range performance.
u The size of the solution is very important.
u As the power of Electronic equipment and transmitters continues to increase, thermal management issues must be resolved.
In order to seek higher data rates to support various wireless services and different transmission schemes, system designers are faced with more complex circuits and must meet similar size, power, and cost budgets. Adding more transceiver channels in the base station tower can achieve higher throughput, but achieving each channel at a higher RF power level is as important as keeping the complexity and cost of the system at an acceptable level. In order to achieve higher RF power, hardware designers do not have many choices in RF front-end design, but rely on traditional solutions that require high bias power and complex peripheral circuits to achieve this, which makes it more difficult to achieve design goals .
ADI recently introduced a multi-chip module suitable for time division duplex (TDD) systems, which integrates low noise amplifiers (LNA) and high power switches. The ADRF5545A/ADRF5547/ADRF5549 series cover the 1.8 GHz to 5.3 GHz cellular frequency band and are optimized for the M-MIMO antenna interface. This new series of devices integrates high-power switches with silicon technology and high-performance low-noise amplifiers with GaAs technology, combining high RF power handling capabilities and high integration without sacrificing any aspect-the best of both worlds.
Dual channel architecture
The application block diagram of ADRF5545A/ADRF5547/ADRF5549 designed by M-MIMO RF front-end is shown in Figure 1. The device channel integrates a high-power switch and a two-stage LNA. While the transceiver is operating in receive mode, the switch routes the input signal to the LNA input. During the transmit mode, the input is routed to the 50 Ω terminal electrode to ensure proper matching with the antenna interface and isolate the LNA from any reflected power from the antenna. The integrated dual-channel architecture allows designers to easily extend MIMO beyond the limitations of traditional device 8×8 (8 transmitter×8 receiver) configurations, reaching 16×16, 32×32, 64×64, and even higher.
Figure 1. Block diagram of M-MIMO radio frequency front end.
Wide working bandwidth
The gain characteristic of ADRF5545A/ADRF5547/ADRF5549 and its frequency coverage are shown in Figure 2. Each device is optimized for commonly used cellular frequency bands and is consistent with other tuning components (such as power amplifiers and filters) used in the same design.
Figure 2. ADRF5545A/ADRF5547/ADRF5549 gain characteristics
High power protection switch
The device contains a high-power switch designed through a silicon process and does not require any external components to generate bias. This switch operates on a single 5 V power supply and consumes only 10 mA. It can be directly connected to a standard digital microcontroller without the need for any negative voltage or level shifters. Compared with the implementation scheme based on PIN diode switches, silicon switches can save users about 80% of bias power and 90% of circuit board space.
The switch can handle a 10 W average RF signal with a peak-to-average ratio (PAR) of 9 dB during continuous operation, and can withstand twice the rated power in the event of a fault. ADRF5545A/ADRF5547/ADRF5549 are the first products on the market with a power handling capability of 10 W, so they are particularly suitable for high-power M-MIMO designs. If each antenna element can transmit more power, then the number of transmission channels can be reduced and the same RF power can be obtained from the base station. The ADRF5545A/ADRF5547/ADRF5549 architecture is shown in Figure 3. It can be seen from it that the high-power switches of the two channels are powered and controlled by the same device pin. LNA has its own power supply and control signal design.
Figure 3. ADRF5545A/ADRF5547/ADRF5549 circuit architecture
Low noise figure
The two-stage LNA is designed through the GaAs process and uses a single 5 V power supply without any external bias inductors. The gain has a flat characteristic in the frequency range, and can be programmed to 32 dB and 16 dB in high gain mode and low gain mode, respectively. The device also has a low-power mode to save bias power, where the LNA can be powered off during transmission operations. The noise figure of this device is 1.45 dB (including the insertion loss of the switch), which is very suitable for high-power and low-power M-MIMO systems. Figure 4 shows the noise figure performance of the ADRF5545A/ADRF5547/ADRF5549 in the specified frequency band.
Figure 4. ADRF5545A/ADRF5547/ADRF5549 noise figure
Small size, minimum number of external components
Except for the primary decoupling capacitors on the power supply pins and the DC blocking capacitors on the RF signal pins, the device does not require any tuning or matching components. The RF input and output are matched at 50 Ω. Matching and biasing inductors are integrated in the LNA design. This reduces the material cost of expensive components (such as inductors) and also simplifies the hardware design of crosstalk between channels between adjacent transceivers. This device is available in a 6 mm × 6 mm surface mount package with a thermally enhanced backplane. The device operates in a rated case temperature range of -40°C to +105°C. All three chips have the same package and use the same pinout configuration. Can be used interchangeably on the same circuit board. Figure 5 shows how the device is mounted on its evaluation board. The evaluation board can be obtained directly from ADI or through its distributors.