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RF & MICROWAVE DESIGN required to avoid interference with other devices on the network. This is done by specifying The Third Order Input Intercept Point (IIP3). Sourcing Intel Mobile Corporation, 2G requirement for switch linearity was IIP3= 55dBm, 3G switch requirement was 65dBm, LTE switch IIP3 requirement is 72dBm and LTE-A antenna switch with UL CA capabilities will have to meet IIP3 of 90dB. Currently, solid-state switch technology such as SOI or SOS is reaching the technology limit and will not be capable of achieving an IIP3 of 90dBm – see figure 2. The problem is their poor Ron*Coff = 120 Figure of Merit (FoM) switch and in OFF-State SOI/SOS transistors leakage, which is affecting switch linearity, insertion loss and isolation. Increasing the number of switch throws for high multi-throw switch configurations and higher frequency bands will further quickly degrade performance and make this type of switch a very poor choice for LTE-A switching. The only type of switch capable of achieving this RF performance of IIP3 >90dBm target is an RF MEMS (Micro Electro Mechanical) switch. DelfMEMS RF MEMS switches are surface micro-machined devices that use a mechanical movement to switch Fig. 3: DelfMEMS RF switch. the RF transmission line on or off – see figure 3. This technology doesn’t suffer from frequency dependency and high multi-throw switch configuration limitation. With its FoM <10 it offers dramatically superior linearity, insertion loss and isolation performance compared to existing solid-state solution. The DelfMEMS switch becomes an ideal solution for typical RF-FE for LTE-A, where low IL is essential. High IL has a direct negative impact on smartphone battery life and Rx Sensitivity degradation, which will directly impact handset call quality and data reception. According to “Top 10 Smartphone Purchase Drivers” user study, battery life is, for over 50% of users, the most important feature in the smartphone. The IL reduction which can be achieved with the DelfMEMS switch in a multi-throw, high frequency environment replacing existing SOI/SOS switches will produce up to 17% battery power saving and up to 29% Rx sensitivity improvement. These exceptional improvements become even greater at 3.5GHz. Equally important are isolation benefits between bands and Rx and Tx. Here the DelfMEMS switch is capable 40dB isolation at 2.7 GHz bands, compared to the existing 18dB solid-state switch isolation. Taken together, it becomes increasingly clear that RF MEMS switches with their inherently high linearity, high operating frequency, ultra-low insertion loss and very high port-to-port isolations are a perfect LTE-A switching candidate. The DelfMEMS RF MEMS switch structure uses a new, integrated, micro-mechanical building block that is based on a robust, totally new IP portfolio that includes seven key patents and innovations. It does not use a cantilever beam or bridge featuring a highly conductive electrode electrostatically actuated in order to create an ohmic contact resulting in a mechanical switching. These older structures proved to have several issues: stress on the anchors, possible stiction, low commutation speed and possible creep of the beam. DelfMEMS innovative design approach has resulted in the development of an anchorless structure for mechanical RF switching which totally overcomes these historical design problems instead of trying to simply reduce them. The solution features a free flexible membrane held by two sets of pillars and stoppers. This membrane is electrostatically actuated by 2 sets of electrodes enabling both contact in ON state and an electrostatically controlled OFF state – see figure 4. Contact can be either attracted to the conductive line or repelled from it. Such capability allows for an increased gap between electrode and transmission line in off-state (directly linked to contact isolation) and allows for resetting the switch in unlikely case of stiction. The use of active actuation also permits the de-correlation between restoring forces, contact forces and 32 Electronic Engineering Times Europe October 2014 www.electronics-eetimes.com


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