Abstract: A filter integrated circuit, including an acoustic wave filter chip and a matching circuit, is provided. The acoustic wave filter chip is covered upon a substrate. The matching circuit is disposed on the substrate to provide matching impedance to the acoustic wave filter chip. A first pad and a second pad of the matching circuit are respectively connected to a first signal terminal and a second signal terminal of the acoustic wave filter chip. First terminals of a first coil inductor and a second coil inductor of the matching circuit are respectively connected to the first pad and the second pad of the substrate. The first coil inductor is adjacent to the second coil inductor, so that mutual inductance and parasitic capacitance are formed, so that the matching circuit and the acoustic wave filter chip jointly generate a transmission zero point located in a triple fundamental frequency range.

Abstract: A duplexer includes first and second acoustic filters and a phase shifter. The first acoustic filter is connected between an antenna and the transmitter, and has a first passband. The second acoustic filter is connected between the antenna and the receiver, and has a second passband. The phase shifter includes at least one series capacitor connected in series with the antenna and at least one shunt inductor connected between the at least one capacitor and ground. The phase shifter is connected between the antenna and the first filter when the first passband is higher than the second passband, and provides a negative phase shift of an output impedance of the first filter. The phase shifter is connected between the antenna and the second filter when the second passband is higher than the first passband, and provides a negative phase shift of an input impedance of the second filter.

Abstract: A duplexer interfacing a receiver and a transmitter with an antenna includes first and second filters. The first filter includes at least four first series resonators, four first shunt resonators respectively connected between the four first series resonators and ground voltage, and a mutual inductance commonly connected between two adjacent first shunt resonators. The second filter includes at least four second series resonators, four second shunt resonators respectively connected between the four second series resonators and the ground voltage, and a cross-coupling capacitor connected between a first capacitor node connected to at least one of the second series resonators and a second capacitor node connected to one of the second shunt resonators, and an inductor connected in series between second capacitor node and ground. Three of the second series resonators and the second shunt resonator to which the cross-coupling capacitor is connected are between the first and second capacitor nodes.

Abstract: A duplexer includes first and second acoustic filters and a phase shifter. The first acoustic filter is connected between an antenna and the transmitter, and has a first passband. The second acoustic filter is connected between the antenna and the receiver, and has a second passband. The phase shifter includes at least one series capacitor connected in series with the antenna and at least one shunt inductor connected between the at least one capacitor and ground. The phase shifter is connected between the antenna and the first filter when the first passband is higher than the second passband, and provides a negative phase shift of an output impedance of the first filter. The phase shifter is connected between the antenna and the second filter when the second passband is higher than the first passband, and provides a negative phase shift of an input impedance of the second filter.

Abstract: A duplexer interfacing a receiver and a transmitter with an antenna includes first and second filters. The first filter includes at least four first series resonators, four first shunt resonators respectively connected between the four first series resonators and ground voltage, and a mutual inductance commonly connected between two adjacent first shunt resonators. The second filter includes at least four second series resonators, four second shunt resonators respectively connected between the four second series resistors and the ground voltage, and a cross-coupling capacitor connected between a first capacitor node connected to at least one of the second series resonators and a second capacitor node connected to one of the second shunt resonators, and an inductor connected in series between second capacitor node and ground. Three of the second series resonators and the second shunt resonator to which the cross-coupling capacitor is connected are between the first and second capacitor nodes.

Abstract: A resonator of a planar circuit type is provided for receiving a signal from an input end and transmitting a signal to an output end. The resonator includes: (a) a dielectric substrate; (b) a ground plane including a layer of conductive material formed on the bottom surface of the substrate; (c) an inductor formed on the top surface of the substrate and connected to the input and output ends; and (d) a series capacitor connected in parallel to the inductor, wherein the series capacitor includes two patches of conductive material formed on the top surface of the substrate, each patch being connected to one respective end of the resonator. Each patch also forms a shunt capacitor with the ground plane, and the capacitance of the shunt capacitor constitutes the majority of capacitance between the ground plane and the end of the resonator that is connected to the patch. The conductive material may be a superconductor, including oxide superconductors.

Abstract: The present invention provides for a method and apparatus to control non-adjacent cross-coupling in a micro-strip filter. In instances of weak cross-coupling, such as a filter circuit on a high dielectric constant substrate material (e.g., LaAIO3 with dielectric constant of 24), a closed loop is used to inductively enhance the cross-coupling. The closed loop increases the transmission zero levels. For strong cross-coupling cases, such as a filter circuit on a lower dielectric constant substrate material (e.g., MgO with dielectric constant of 9.6), a capacitive cross-coupling cancellation mechanism is introduced to reduce the cross-coupling. In the latter instance, the transmission zero levels are moved down.