A low impedance VHF micromechanical filter using coupled-array composite resonators

By using mechanically-coupled flexural-mode square resonator arrays as "composite" resonators, the impedance of a 68.1-MHz (VHF), capacitively-transduced micromechanical filter has been lowered to point of allowing L-network-aided matching to 50Ω termination impedances, while also exhibiting less than 2.7dB insertion loss (IL) for a 190kHz passband width (0.28% bandwidth). The use of composite arrays to replace previous single resonators in a series filter topology not only allows a reduction in filter termination resistance by a factor ideally equal to the number of resonators in the array, but also a reduction in filter bandwidth by this same factor $an important feature for channel-select applications. Although array Q values are smaller than the Q of a stand-alone square resonator, they are still sufficient for excellent filter performance.