Patent attributes
A filter structure, comprising a first signal line, a second signal line, a third signal line and a fourth signal line, said first and third signal lines defining an input port and said second and fourth signal lines defining an output port of a section of said filter structure, said section being defined by a first bulk acoustic wave resonator (A) which is connected between said first signal line and said second signal line, a second bulk acoustic wave resonator (G) which is connected between said third signal line and said fourth signal line, a third bulk acoustic wave resonator (C) which is connected between said first signal line and said fourth signal line, and a fourth bulk acoustic wave resonator (E) which is connected between said second signal line and said third signal line; is characterized in that a frequency pulling factor defined d of at least one of said acoustic wave resonators is non-zero, said frequency pulling factor d being defined by for first and second bulk acoustic wave resonators having a resonant frequency fr1, and for third and fourth bulk acoustic wave resonators having an anti-resonant frequency fa2, f0 being the centre frequency of the filter structure and k the coupling factor of respective resonators.
