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Nanusens Limited

Nanusens Limited

DTCs for 5G Back to Exhibitor Page

The pioneer of MEMS-within-CMOS™, Nanusens, will soon be shipping evaluation samples of its new product line, RF Digital Tunable Capacitors (DTCs). These solve the problem of current 5G antenna solutions that become increasingly power hungry in the higher 5G bands. The key is the very high Q factor of above 100 at 1GHz and, importantly, the Q factor continues to be high up through to the higher 5G bands to keep power losses very low, where the Q factor of rivals drops down significantly. Nanusens DTCs thus open up the power efficient use of higher 5G bands. The DTCs are created using the company’s award-winning techniques of creating nanostructure within CMOS using only standard techniques in a CMOS fab so there are no limits on production volumes. Also, because they are created in CMOS, they can be built simultaneously with other structures on a chip, giving a lower BOM. The global market for antenna tuners was $514M in 2018 and is forecast to grow to $1200M by 2025 as 5G rolls out. The increasing number of 5G phones means that the higher 5G bands will start to be needed to accommodate the extra traffic. To do this requires additional antennas to be integrated into the phone to handle more 5G bands but, due to them having to be smaller to fit more of them inside the phone, their efficiency decreases. In order to get the best possible performance from each antenna, each has to be tuned to prevent a mismatch between the RF front end and the antenna that would result in losses. This is done with an antenna tuner -- either a solid-state switch or an RF MEMS tunable capacitor but each approach has its own drawbacks. The problem with solid-state switches is that they have a low Q factor, which is a measure of the performance with higher Q factors being better as these indicate lower losses during operation. Solid-state switching solutions’ low Q factor is due to their ON state (Ron) resistance. This becomes worse as the frequency goes up to the higher 5G bands, which has become a limiting factor in using these higher bands effectively. With RF MEMS tuneable capacitors, the issue is poor reliability as they use dielectric. This can suffer from dielectric charging which is the main cause of failure in RF MEMS devices and also limits the peak-to-peak voltages that they can withstand before dielectric breakdown.Nanusens has created a solution that avoids both problems. It uses an array of RF MEMS digital tuneable capacitors (DTCs) and opens up the implementation of antenna tunning for the higher 5G bands due to their better Q factors for these bands. This solves the low Q factor problem as there is no ON state resistance in this design resulting in a very high Q factor of above 100 at GHz and, importantly, the Q factor continues to be high up through to the higher 5G bands to keep losses very low, where the Q factor of rivals drops down significantly. The RF MEMS issues of dielectric charging and/or breakdown do not exist as no dielectric is used in this innovative design. This results in far superior reliability and, as a result, the Nanusens DTCs have successfully passed over four billion test cycles in the lab. The key factors for DTCs are the Q factor and linearity. The Q factor is above 100 at 1GHz, which matches state-of-the-art RF MEMS solutions and is well above solid-state switching solutions. They also show excellent linearity with more than the 90 dBc for IMD3 which is the 5G requirement. Minimum capacitance can be kept very small -- down to Coff of 30 fF for a single capacitor off state (that means a Cmin of 0.45 pF for a 4-bit DTC) and even less for future iterations. Similarly, the capacitance ratio is currently 2 and Nanusens expects to improve on this with the next product iteration to 3.

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