Improvement of non-linear performance in BAW filters using balancing capacitors

The constantly rising demand for higher data rates is addressed by advanced communication standards like carrier aggregation (CA) in combination with LTE. The increased complexity of the RF frontend has put tremendous pressure on improving linear performance of BAW filters over the last years. On top of that a large number of intermodulation (IMD) specification have been added to safeguard all CA modes. It is obvious that improving intrinsic linearity on a filter level is of great advantage. Doubling up resonators in perturbing stages is a common approach to decrease non-linear contribution in a filter as power density in resonators decreases and - in theory - a perfect cancellation of non-linear 2nd order response occurs when the resonators are connected such that they operate in anti-phase. Focusing on cascaded resonator stages, the authors present a novel way to achieve improved cancellation so resonator stages exhibit an even more linear behavior than for the regular cascaded pair.