The main advantages of the RF MEMS switch are very low insertion loss, a high level of isolation, low level harmonic distortion and very high linearity irrespective of the number of throws. Compared to SOI, MEMS technology demonstrates significant advantages in terms of RF performances.
The case for RF MEMS is simple: it is absolutely critical to provide RF switches in multi-throw configurations with very low insertion loss and superb linearity and isolation for critical applications where minimizing linear power loss is crucial. Using MEMS switches, the design configuration can be scaled up rather easily to a very large throw counts without a large increase in parasitics.
Front-End module makers are pushing very hard to have the lowest nominal insertion loss in all bands and significantly better linearity and isolation compared to what is available today in the solid state approaches. Employing RF MEMS switches in the system architecture design provides solutions for high frequency BAW and FBAR filters and LNAs elimination/simplification, and 4G designs that will enable Up Link Carrier Aggregation and ensure the achievement of some of the most critical LTE and LTE-A mode specifications.
The DelfMEMS RF MEMS switching solutions provides very low insertion loss, feature superb linearity, and provide high isolation. These factors combine to improve receiver sensitivity, enable Uplink Carrier Aggregation (which isn’t possible with existing technology), and provide a huge reduction in power consumption (up to 20 percent saving in the RF Front-End module of the phone). It also provides a significant reduction in the bill of materials cost for the phone, since the duplication of some multiple RF component paths is eliminated.
Carrier Aggregation – enabling faster data rates
One of the biggest challenges is LTE carrier aggregation. This is a technique used in the LTE Advanced standard to increase bandwidth and thereby increase bit rates. Mobile handsets must be capable of simultaneous reception and transmission of two or more carriers. This brings new challenges when designing for the LTE Advanced standard. For example, carrier aggregation will undoubtedly pose major difficulties for the mobile handset RF section which handles multiple and simultaneous transmit and receive paths.
The addition of simultaneous, non-contiguous transmitters creates a highly challenging radio environment in terms of spur management and self-blocking. Intermediation created by active components of the RF Front-End will become crucial for LTE Advanced implementation.
If we take into account the amount of the RF Front-End insertion loss, a reduction of only 0.5 dB to 1dB will represent a significant difference in future 4G systems. Linear power will be at a premium. Although these savings in linear power might seem small, a stable, low insertion loss across all LTE bands will allow significant architecture simplification.
When considering the power amplifier, insertion loss following power amplification degrades the power efficiency. An insertion loss decrease of 0.5 dB to 1 dB per throw, considering only the antenna switch, will generate a 10 to 20 % absolute level efficiency improvement. This can be even further improved by using RF MEMS technology for PA band select switching.
A decrease of harmonic distortion is yet another necessary advantage. The power in full duplex systems must deliver through a highly specified (linear) RX/TX switch. A half duplex switch also needs low harmonics. However, if both half and full duplex paths must be supported, then the design and implementation become challenging (particularly when all the other existing switch paths are taken into consideration).
From the point of view of the load on the PA, noise due to harmonic distortion results in reduced power efficiency. Experiments have shown that a decrease of harmonic distortion can also substantially improve the power efficiency. The power consumption at the module level, especially for 4G LTE, can then be managed more effectively.