Bulk acoustic wave filter circuit having phase cancelling circuit
Aspects and examples provide improvement in the attenuation level near the passband within the stopband of the bandpass-type filter using a ladder-type circuit. In one example the ladder-type circuit is formed from bulk acoustic wave resonators. A loop circuit is connected between two distinct points on a signal path extending from an input to an output of the ladder-type circuit for phase-cancellation of signals at the two distinct points. The two distinct points may be the input and the output of the ladder-type circuit. The loop circuit may include a coupled bulk acoustic wave resonator.
1 . A filtering circuit comprising:
a ladder-type filter having an input and an output, the ladder-type filter including a plurality of series-arm acoustic wave resonators connected in series along a signal path between the input and the output, and a plurality of parallel-arm acoustic wave resonators connected between the signal path and a ground; and
a loop circuit connected in parallel with the ladder-type filter between the input and output, the loop circuit including a first capacitor connected to the input, a second capacitor connected to the output, and a coupled bulk acoustic wave resonator connected to 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 first capacitor being integrally formed with the coupled bulk acoustic wave resonator and including a portion of a conductive trace forming an upper electrode of the first acoustic wave element and a lower plate separated from the conductive trace by a layer of dielectric material, the lower plate being laterally displaced from the piezoelectric film.
2 . The filtering circuit of claim 1 wherein each acoustic wave resonator is a film bulk acoustic wave resonator.
3 . The filtering circuit of claim 1 wherein each acoustic wave resonator is a solidly mounted resonator.
4 . The filtering circuit of claim 1 wherein the first and second acoustic wave elements of the coupled bulk acoustic wave resonator are film bulk acoustic wave resonators.
5 . The filtering circuit of claim 1 wherein the second capacitor is integrally formed with the coupled bulk acoustic wave resonator.
6 . The filtering circuit of claim 5 wherein the second capacitor is formed from a portion of a conductive trace forming an upper electrode of the second acoustic wave element and a lower plate separated from the conductive trace by a layer of dielectric material.
7 . 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, the first capacitor being integrally formed with the coupled bulk acoustic wave resonator and including a portion of a conductive trace forming an upper electrode of the first acoustic wave element and a lower plate separated from the conductive trace by a layer of dielectric material, the lower plate being laterally displaced from the piezoelectric film.
8 . The filtering circuit of claim 7 wherein each series-arm acoustic wave resonator and each parallel-arm acoustic wave resonator is a bulk acoustic wave resonator.
9 . The filtering circuit of claim 8 wherein each bulk acoustic wave resonator is one of a film bulk acoustic resonator and a solidly mounted resonator.
10 . The filtering circuit of claim 7 wherein the first and second acoustic wave elements of the coupled bulk acoustic wave resonator are film bulk acoustic wave resonators.
11 . The filtering circuit of claim 7 wherein the second capacitor is integrally formed with the coupled bulk acoustic wave resonator.
12 . The filtering circuit of claim 7 wherein the second capacitor is formed from a portion of a conductive trace forming an upper electrode of the second acoustic wave element and a lower plate separated from the conductive trace by a layer of dielectric material.
13 . 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, the first capacitor being integrally formed with the coupled bulk acoustic wave resonator and including a portion of a conductive trace forming an upper electrode of the first acoustic wave element and a lower plate separated from the conductive trace by a layer of dielectric material, the lower plate being laterally displaced from the piezoelectric film.
14 . The filtering circuit of claim 13 wherein the first node is the input of the primary filter and the second node is the output of the primary filter.
15 . The filtering circuit of claim 13 wherein the first node is the input of the primary filter, a first parallel-arm acoustic wave resonator of the plurality of parallel-arm acoustic wave resonators is connected between the second node and the ground, and at least one series-arm acoustic wave resonator of the plurality of series-arm acoustic wave resonators is connected between the second node and the output of the primary filter.
16 . The filtering circuit of claim 13 wherein each of the primary acoustic wave resonators is one of a film bulk acoustic resonator and a solidly mounted resonator.