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Small RF filters handle multiple bands in single die

Posted: 27 Aug 2015 ?? ?Print Version ?Bookmark and Share

Keywords:radio frequency? RF filter? surface acoustic wave? smartphone? bulk acoustic wave?

Resonant's already successful superconductor filterswhich it claims are the highest performance filters ever madeuse micro-strip resonators with a Q in excess of 100,000, making them very selective and low loss. Resonant also makes the helium-powered "cold box" about the size of a small load of bread that keeps the superconducting filters at 77-degrees Kelvin with an expected lifetime of 100 years.

Its fixed frequency SAW filters for consumer products are built on the circuit theory it developed for its superconducting filters, but adapted to room temperature. Resonant estimates that they have 50,000 man-hours of R&D invested in its consumer SAW filters.

Almost half of a smartphone RF front-end today is occupied by all the RF filters it needs, according to Resonant, and the situation will only get worse with 5G, which uses band aggregation for higher-data rates, plus multiple antennas all of which require their own RF filters.

RF front-end industry

RF filters are the fastest growing segment of the RF front-end industry for smartphones and Internet of Things (IoT) devices capturing nearly 50 per cent of the market (approx. $8 billion) by 2020. (Source: Mobile Experts LLC)

Avago, Skyworks and even Qualcomm all need smaller more versatile filters, any of which they will incorporate inside the package of their RF front-end chip sets. Resonant claims its smaller higher performance RF filters will allow RF front-end makers to increase performance while shrinking sizes by incorporating the filters and duplexers inside the same package.

"Plus we are promising an 80 per cent size reduction over the next two to three years," Hammond told us. "We are also designing super-accurate temperature compensated surface acoustic wave [TC-SAW] already, which outperform our competitors bulk acoustic wave [BAW] filters."

RF filter process

Today's RF filter process (top) has been the same since the 1920s, but Resonant has modernised the process to take advantage of the latest design techniques, enabling it to become the world's first fabless RF manufacturer. (Source: Resonant)

To work its magic, Resonant has created its own all-custom software tool kitsone for superconductors, one for electromagnetic modelling and one for acoustic modelling.

"All three of our tool kits start from first principles and go all the way down to the nanoscale," Hammond told us. "Everything is custom and much faster than traditional tools plus we have a software team which is always improving them to keep them ahead of the commercial tools."

The tape-outs from its tools are compatible with the manufacturing methods of any fab that makes RF front ends, one of which Resonant has already transferred its IP. A second fab will come online by the end of 2015 to meet the demand of its two new consumer customers and its just getting started with a third fab to meet expected demand in 2016 and beyond.

- R. Colin Johnson
??EE Times U.S.

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