23 March 2014

GE introduces awesome MEMS switch tech for faster LTE-Advanced

GE MEMS switch on a dime
This week, GE Global Research announced it had developed a brand new switch technology that can be used for enhancing the radios used in 4G phones to provide much faster speeds. Called a “MEMS switch,” it promises to drastically improve the efficiency and performance of radio signals.

To understand how this improves LTE performance, we need to understand how this MEMS (microelectromechanical system) switch fits into the equation. In the radio chain (comprising of the antenna, filters/duplexers, power amplifiers, transceiver, and the baseband), there are RF switches used everywhere. RF switches are used to support multiple bands within a frequency range. For example, an antenna for 1710-2170 MHz would have switches to support 2.1GHz (IMT, 3GPP Band 1), 1.9GHz (PCS, 3GPP Band 2/25), 1.8GHz (DCS, 3GPP Band 3), and 1.7+2.1 GHz (AWS, 3GPP Band 4/10).

RF switches in radios typically leak some of the signal out, causing interference and signal quality degradation before it even leaves the phone (or in the case of received signal, before it even reaches the baseband for processing). With older technologies (like GSM, CDMA, and UMTS), this generally resulted in lower coverage (i.e. fewer bars). There was also a performance drop, but the coverage was the main issue.

With LTE, though, you suffer a lot more on performance. This is largely because there are a lot more complex radio techniques being used to improve capacity and latency, and these techniques require much more sensitive radio equipment. Consequently, that leakage that only hurt a little bit before will hurt a lot now.

Current RF switches are transistor based, meaning that they are semiconductors. GE’s MEMS switches are the closest it gets to a wire-based switch, as it is a metal/metal contact switch controlled by using electrostatic forces. As a consequence, these switches are as nearly totally lossless as it gets for switches. Also, GE’s technology is designed to have better inherent isolation for each switch within an array of switches, so that when a switch is flipped, there will not be anything leaking over from one side of the switch to the other (reducing or eliminating potential interference issues from triggering multiple conditions at once).

GE MEMS switch wafer

A wafer of GE MEMS switches

With a high degree of isolation, linearity (degree to which the component does not affect the signal being carried), and a very low degree of loss across a chain of switches (which is critical for signal transference across the radio chain in mobile devices), RF switches based on GE’s MEMS technology would be perfect for improving the base hardware that all cellular networks run on. It also helps that it’s quite small! (In the top image, the MEMS switch is shown on top of a US dime, which is 18mm across.) Low-throw-count switches (2-6 count) are comparable to the currently used technology in size (silicon on insulator, or SOI for short), but high-throw-count switches (12+) would be significantly smaller than any of its competitors. That enables smaller form factors and reduced costs on PCB construction.

The result of this improved technology is that the signal goes in and out of the device more more cleanly. As GE mentions in its announcement, less distortion and leakage leads to a cleaner signal that can be processed and used with more advanced radio techniques like higher-order MIMO and non-contiguous carrier aggregation. It also allows for more sensitive radios to be used. This is critical for LTE-Advanced, as those technologies are the core of how it offers super-fast broadband connectivity.

Now, MEMS has been around for a long time. The benefits of MEMS switches are not new. However, what is new is GE’s production process involving a metal alloy that makes it possible to use it in low-power environments like smartphones as well as higher-power environments like cell towers. This “secret sauce,” as GE Ventures’ Chris Giovanniello called it, is what makes it usable for these environments. Giovanniello further noted that since GE does not participate in the wireless industry, it will be looking to license out its technology to companies that do (such as network gear and smartphone vendors) to enable wide adoption of “GE Metal MEMS” RF switches.

As of right now, no one has announced any partnerships to use the technology, but it wouldn’t be surprising if the next generation of LTE-Advanced network gear and devices used the technology to enable much better performance in the network.



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