RF Switch Ups Power Density and Integration for 5G Networks
The new RF switch device from Menlo Micro offers 25 W power handling and an integrated charge pump driver circuit.
As 5G network services deploy across the globe, demand is on the rise for sub-6 GHz—and for the C-band spectrum in particular. Such mid-band 5G networks rely on key infrastructure that includes advanced beamforming antennas and similar applications.
Those system designs call for highly reliable, high-performance RF switching technology. With that in mind, Menlo Micro has rolled out its MM5140 switch aimed at those needs. The MM5140 is a single-pole/four-throw (SP4T) DC-to-6 GHz switch.
The 5.2 mm x 4.2 mm MM5150 RF switch is shown here on an evaluation kit board. Image used courtesy of Menlo Micro
Key specs include:
- 25 W (continuous wave), 150 W (pulsed) maximum power handling
- -40°C to +85°C temperature range
- Operating lifetime: >3 billion switching cycles
- Linearity IP3 (3rd order intercept point) greater than 90 dBm
In this article, we share insights from our conversation with Menlo Micro. We look at how its switch technology contrasts with GaN (gallium nitride)-based solutions. We also get the company’s take on what specs are important for applications like 5G beam-steering and the significance of the integrated charge pump driver.
Tradeoffs to RF Switch Design Approaches
Like Menlo Micro’s other RF switch products, the MM5150 is built using the company’s “Ideal Switch” technology. The approach uses a mix of materials and semiconductor-like manufacturing techniques, while other RF switches on the market instead use a single semiconductor technology, like GaN.
In our interview, we asked Jonathan Leitner, Senior Product Marketing Engineer at Menlo Micro, how their technology approach contrasts with semiconductor-based technologies like GaN. Leitner says that Menlo’s “Ideal Switch” technology provides some important advantages over GaN in thermal performance, DC, and RF performance.
While GaN has a semi-insulating substrate, Menlo’s approach uses a metal alloy switch technology combined with a fully insulating glass substrate, says Leitner.
Through-glass-via packaging is a key part of the "Ideal Switch” technology. Screenshot used courtesy of Menlo Micro
This results in improved RF linearity (IIP3), much lower harmonics, lower RF losses, and improved DC leakage currents.
Those specs are important, but there are tradeoffs. For example, GaN switches don’t require a high voltage bias to actuate the switch, but Menlo’s switch does since they are electrostatically actuated. Like other semiconductor switches, GaN switches have turn-on/turn-off rates that are often a factor of 10x faster than Menlo’s Ideal Switch products.
Integrated Charge Pump Driver
According to Leitner, a key innovation of the MM5140 switch is that it integrates a high-voltage charge pump/driver circuit. This shrinks the need for external components while also allowing simpler PCB designs.
We asked Leitner what some of the implications are of this integrated charge pump circuitry. As mentioned earlier, Menlo’s switches are electrostatically actuated, and this requires a high voltage/low current biasing source. Leitner says this has presented problems for some engineers, but now that issue can be eliminated because of the integrated custom-designed charge pump/driver circuit.
Functional block diagram of the MM5150. The integrated charge pump driver circuit eliminates the need for several external components. Image used courtesy of Menlo Micro
Other solutions often require multiple discrete charge pump and driver/multiplexing circuits, he says, but without achieving the small size and interface options of Menlo’s charge pump/driver design.
The integrated charge pump circuit provides flexible SPI and GPIO digital interfaces. This means that it can be controlled easily from a host processor or test system, according to the company.
5G Beam Steering Use Case Example
As mentioned earlier, the MM5140 switch features specs that make it suited for demanding applications, including a wide temperature range and good linearity. We asked Leitner to expand on why those attributes are important for a system design such as an RF beam-steering antenna for example.
"The challenge of 5G beam steering antennas is that today’s remote mechanical phase shifters offer very high levels of linearity (greater than 100 dBm), but they are large and bulky. That high linearity is a requirement to maintain low adjacent channel leakage performance such that the transmitter does not interfere with adjacent cell channels."
The trick then is providing high linearity using technology that can enable smaller and more integrated designs. Leitner claims that there are currently no known semiconductor processes and RF switches that can approach the >90 dBm IP3 of the MM5140.
That’s the level of linearity needed to compete with the levels provided by traditional mechanical phase shifters that drive the antenna elements, he says.
Smaller Designs Solving Big Problems
The company says engineering samples of the MM5140 SP4T switch are available now, along with evaluation boards. Scheduled for production release is Q2 2022. With 5G network gear rolling out worldwide, engineers are looking to improve and evolve their system designs. It’s always a game of tradeoffs, but Menlo’s MM5140 RF switch may offer a way to rethink what can be done in terms of component count and RF performance.