Want to save bias power in MIMO RF front-end designs? High-power silicon switches are the answer

This achievement has been made possible by the availability of highly integrated single-chip RF transceiver solutions, such as the ADRV9008/ADRV9009 product family from ADI. Similar integration is still needed in the RF front-end portion of such systems to reduce power consumption (to improve thermal management) and size (to reduce cost) to accommodate more MIMO channels.

* The ADRV9009 is the only single-chip solution that meets all existing and emerging cellular standards – from legacy 2G/3G protocols to the higher data rates required by 4G and the emerging needs of 5G.

MIMO architectures allow for the relaxation of RF power requirements for building blocks such as amplifiers and switches. However, as the number of parallel transceiver channels increases, the complexity and power consumption of the peripheral circuits also increase accordingly. ADI's new high power switches using silicon technology are developed to simplify RF front-end design, eliminate the need for peripheral circuits and reduce power consumption to negligible levels. ADI's new high power switches using silicon technology provide RF designers and system architects with the flexibility to increase the complexity of their systems without making the RF front end the bottleneck of their design.

In time division duplex (TDD) systems, a switch function is incorporated into the antenna interface to isolate and protect the receiver input from the transmitted signal power. This switch function can be used directly at the antenna interface (in relatively low power systems, as shown in Figure 1) or in the receive path (for higher power applications, as shown in Figure 2) to ensure proper connection to the duplexer. Having a parallel branch on the switch output will help improve isolation performance.

Figure 1. Antenna switch.

Figure 2. LNA protection switch

PIN diode-based switches have been the preferred solution due to their low insertion loss characteristics and high power handling capabilities. However, in the design of massive MIMO systems, they require high bias voltage for reverse bias (for isolation) and high current for forward bias (for low insertion loss), which becomes a disadvantage. Figure 3 shows a typical application circuit for a PIN diode-based switch and its peripherals. Three discrete PIN diodes are biased by their bias supply circuits and controlled by a high voltage interface circuit.

Figure 3. PIN diode switch.

ADI's new high-power silicon switches are better suited for massive MIMO designs. They operate from a single 5 V supply, have a bias current of less than 1 mA, and require no external components or interface circuits. The internal circuit architecture is shown in Figure 4. The FET-based circuit operates with low bias current and low supply voltage, thus pulling power consumption down to negligible levels and helping thermal management at the system level. In addition to ease of use, the device architecture also provides better isolation performance because more parallel branches are included in the RF signal path.

4. ADRV9008/ADRV9009 Silicon Switch

Figure 5 shows a side-by-side comparison of printed circuit board (PCB) artwork for a PIN diode-based switch and a new silicon switch on a single-layer PCB design. The silicon switch occupies less than 1/10 the PCB area of ​​the PIN diode-based switch. It simplifies power supply requirements and eliminates the need for high-power resistors.

Figure 5. Side-by-side comparison of a PIN diode-based switch design and a silicon switch.

ADI's high power silicon switches can handle up to 80 W of RF peak power, which is sufficient to meet the peak-to-average power ratio requirements of massive MIMO systems with margin. Table 1 lists ADI's high power silicon switch series optimized for different power levels and various package types. These devices inherit the inherent advantages of silicon technology and can achieve better ESD robustness and reduce part-to-part variation compared to alternative solutions.

Table 1. ADI's new high power silicon switch series

Massive MIMO systems will continue to evolve and will require further integration. ADI's new high power silicon switch technology is well suited for multi-chip module (MCM) designs, integrating the LNA together to provide a complete, single-chip solution for TDD receiver front ends. In addition, ADI will also increase the frequency of new designs and will lead similar solutions for millimeter wave 5G systems. As ADI expands its high power silicon switch product line to X-band frequencies and higher popular frequency bands, circuit designers and system architects will also benefit from ADI's new silicon switches in other applications, such as phased array systems.