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Tunable RF

One of the more delicate parts of a cellphone is the RF circuitry responsible for getting the signals into and out of the phone.  According to UCSD’s Prof. Gabriel Rebeiz (who presented at the MEMS Business Forum, and who’s actually a pretty entertaining presenter), RF performance has been degrading from generation to generation as the number of bands has increased. From 4G on, he points to the need for better antennas, power amps, and filtering – as well as MIMO technology – in order to improve things.

And tunable RF circuits using MEMS-based variable capacitors seems to be what can get us there. He runs a lab that tests out the various solutions available, and he says that the MEMS versions are amazingly linear, with low loss, high quality, and other favorable characteristics. He paints them as 5 – 10 times better than silicon-on-insulator (SOI), silicon-on-sapphire (SOS), or barium strontium tinanate (BST) tuners.

He sees tunable antennas being common in 2013 and 2014, followed by tunable power amps, then notch filters, and then bandpass filters (if there are any). The two MEMS players that lead in the cellphone space and that presumably will be facilitating this change are WiSpry and Cavendish Kinetics.

But he also sees needs in base stations, instrumentation, defense, satellite communications, and automatic test equipment. And he waxed effusive over the performance of Omron’s MEMS switch, which dominates in this market. He simply calls it “amazing,” the “best RF MEMS switch in the world.”

The one gotcha for all of this, however, is cost. It must be low – 20 – 25 cents for a variable capacitor in a phone. He points to integrated CMOS and RF MEMS as the way to make this happen. Cavendish Kinetics’ technology is CMOS compatible; WiSpry includes CMOS on their chips. So now we just have to watch to see whether the prices get to where they need to be.

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