A multilayer filter includes dielectric layers, a first terminal, a second terminal, a first inductor, a second inductor, and first to fifth capacitors. In a stacking direction of the dielectric layers, at least one of a first air-core portion defined by the first inductor and a second air-core portion defined by the second inductor includes, in a region from the first inductor layer to the second inductor layer, a region enabling magnetic flux to pass therethrough without being obstructed by the first to fifth capacitors and the third inductor.

A diplexer includes a first filter circuit including a first loop inductor defining a first loop plane and a second loop inductor defining a second loop plane, a second filter circuit adjacent to the first filter circuit, and a first via hole conductor that electrically connects an input/output terminal, the first filter circuit and the second filter circuit to each other. The first loop plane faces the second loop plane while protruding beyond the second loop plane in a first direction. The first via hole conductor is provided relative to the first loop inductor in a second direction from the first loop plane toward the second loop plane, and is superposed with a portion of the first loop plane that protrudes beyond the second loop plane when viewed in the second direction.

A diplexer includes a first filter circuit including a first loop inductor defining a first loop plane and a second loop inductor defining a second loop plane, a second filter circuit adjacent to the first filter circuit, and a first via hole conductor that electrically connects an input/output terminal, the first filter circuit and the second filter circuit to each other. The first loop plane faces the second loop plane while protruding beyond the second loop plane in a first direction. The first via hole conductor is provided relative to the first loop inductor in a second direction from the first loop plane toward the second loop plane, and is superposed with a portion of the first loop plane that protrudes beyond the second loop plane when viewed in the second direction.

A filter module includes an antenna connection terminal, filter elements, and inductors. The filter elements are connected to an antenna connection terminal. A first inductor is connected between the antenna connection terminal and the filter elements. A second inductor is connected between a transmission line, which connects the first inductor and the filter elements, and a ground reference potential. The filter elements are on an insulating multilayer substrate. The inductors include electrodes on the multilayer substrate. Inductor electrodes of the first inductor and central cavities of the inductor electrodes are at positions different from other electrodes inside the multilayer substrate.

A filter module includes an antenna connection terminal, filter elements, and inductors. The filter elements are connected to an antenna connection terminal. A first inductor is connected between the antenna connection terminal and the filter elements. A second inductor is connected between a transmission line, which connects the first inductor and the filter elements, and a ground reference potential. The filter elements are on an insulating multilayer substrate. The inductors include electrodes on the multilayer substrate. Inductor electrodes of the first inductor and central cavities of the inductor electrodes are at positions different from other electrodes inside the multilayer substrate.

A branching device (10) includes a switch (SW1), a fixed filter circuit (11), and a tunable filter (TF1). The switch (SW1) includes a common terminal (Ps11) and individual terminals (Ps12, Ps13). The fixed filter circuit (11) is connected to the individual terminal (Ps12) and has a fixed pass band. The tunable filter (TF1) is connected to the individual terminal (Ps13) and has a tunable pass band. The fixed filter circuit (11) includes filters (FIL1, FIL2) having different pass bands. The pass bands of the filters (FIL1, FIL2) correspond to frequency bands to be used in carrier aggregation.

A branching device (10) includes a switch (SW1), a fixed filter circuit (11), and a tunable filter (TF1). The switch (SW1) includes a common terminal (Ps11) and individual terminals (Ps12, Ps13). The fixed filter circuit (11) is connected to the individual terminal (Ps12) and has a fixed pass band. The tunable filter (TF1) is connected to the individual terminal (Ps13) and has a tunable pass band. The fixed filter circuit (11) includes filters (FIL1, FIL2) having different pass bands. The pass bands of the filters (FIL1, FIL2) correspond to frequency bands to be used in carrier aggregation.

A filter is disposed on a base board. The filter includes a first portion, a second portion, a ground portion, a first coupling portion and a second coupling portion. The first portion is disposed on a first layer in the base board to input signals. The second portion is disposed on the first layer to output signals. The ground portion is disposed on a second layer in the base board. The first coupling portion is disposed on the first layer. The first coupling portion is electrically coupled to the first portion and the second portion. The first coupling portion is electrically coupled to the ground portion through via holes. The second coupling portion is disposed on the first layer. The second coupling portion is electrically coupled to the first portion and the second portion. The second coupling portion is electrically coupled to the ground portion through the via holes.

A filter is disposed on a base board. The filter includes a first portion, a second portion, a ground portion, a first coupling portion and a second coupling portion. The first portion is disposed on a first layer in the base board to input signals. The second portion is disposed on the first layer to output signals. The ground portion is disposed on a second layer in the base board. The first coupling portion is disposed on the first layer. The first coupling portion is electrically coupled to the first portion and the second portion. The first coupling portion is electrically coupled to the ground portion through via holes. The second coupling portion is disposed on the first layer. The second coupling portion is electrically coupled to the first portion and the second portion. The second coupling portion is electrically coupled to the ground portion through the via holes.

Disclosed examples include digital isolator modules, isolation circuitry and low-loss multi-order bandpass filter circuits, including a capacitive coupled galvanic isolation circuit with first and second coupling capacitors individually including a first plate and a second plate, and a bond wire connecting the first plates of the coupling capacitors, a first circuit with a first inductor coupled to form a first resonant tank circuit with a first parasitic capacitor associated with the second plate of the first coupling capacitor, and a second circuit with a second inductor coupled to form a second resonant tank circuit with a second parasitic capacitor associated with the second plate of the second coupling capacitor.