Integrated filter and impedance matching network
View Patent ↗A filter and impedance matching network uses acoustic resonators in place of capacitors. A resonator, e.g. FBAR, behaves similar to a capacitor outside of its resonant frequency and so does not impact the function of the network, outside of its resonant frequency. At this resonant frequency, the resonator quickly transitions from capacitor to short circuit to open circuit and back to capacitor. Thus, the will deliver open and short circuits independent of the standard LC filter resulting in a structure with an additional notch, a notch with the characteristics delivered by a very high quality resonator. This notch can be much sharper and closer to the pass band than is possible with ordinary inductors and capacitors.
1. A filter comprising:
a first plurality of acoustic resonators electrically connected in series;
a first plurality of inductors, each inductor connecting between at least one of the acoustic resonators and ground;
a second plurality of inductors, each inductor interposing two of the plurality of acoustic resonators; and
a second plurality of resonators, each resonator connected in parallel to one of the first plurality of inductors;
wherein at least one frequency is notched out in the frequency response.
2. A filter, as defined in claim 1 , wherein one of the first and second pluralities of acoustic resonators is selected from a group that includes film bulk acoustic resonators and surface wave resonators.