Bulk acoustic wave filter circuit having phase cancelling circuit

A filtering circuit comprising:

• a ladder-type filter including a plurality of series-arm acoustic wave resonators connected in series along a signal path between an input and an output, the ladder-type filter further including a plurality of parallel-arm acoustic wave resonators connected between the signal path and a ground;
• and
• a loop circuit including a first capacitor, a second capacitor, and an acoustic wave filter connected in series between the first capacitor and the second capacitor, the first capacitor connected to the input, and the second capacitor connected to a node along the signal path, a first parallel-arm acoustic wave resonator of the plurality of parallel-arm acoustic wave resonators being connected between the node and the ground, and a single series-arm acoustic wave resonator of the plurality of series-arm acoustic wave resonators being connected between the node and the output, the acoustic wave filter including a coupled bulk acoustic wave resonator connected between the first and second capacitors and including a first acoustic wave element having a first signal terminal coupled to the first capacitor, a second acoustic wave element having second signal terminal coupled to the second capacitor, and a ground terminal, the coupled bulk acoustic wave resonator further including a piezoelectric film disposed between the first and second signal terminals and the ground terminal.

A filtering circuit comprising:

• a primary filter including a plurality of primary acoustic wave resonators constructed and arranged to provide the primary filter with a passband and a stopband, the plurality of primary acoustic wave resonators including a plurality of series-arm acoustic wave resonators connected in series along a signal path between an input of the filtering circuit and an output of the filtering circuit, and a plurality of parallel-arm acoustic wave resonators connected between the signal path and a ground;
• and
• a loop circuit including a first capacitor, a second capacitor, and an acoustic wave filter connected in series between the first capacitor and the second capacitor, the first capacitor connected to a first node of the primary filter, the second capacitor connected to a second node of the primary filter that is different than the first node, the acoustic wave filter including a coupled bulk acoustic wave resonator connected between the first and second capacitors and including a first acoustic wave element having a first signal terminal coupled to the first capacitor, a second acoustic wave element having second signal terminal coupled to the second capacitor, and a ground terminal, the coupled bulk acoustic wave resonator further including a piezoelectric film disposed between the first and second signal terminals and the ground terminal, the loop circuit being configured to attenuate a portion of a signal in the stopband of the primary filter by signal phase cancellation.