A filter device includes a multilayer substrate, an inductor, and a first open stub. The multilayer substrate includes a first wiring layer, a second wiring layer including a first reference electrode to which a reference potential is supplied, and a plurality of first dielectric layers between the first wiring layer and the second wiring layer. The inductor has one end coupled to a first terminal and another end coupled to a second terminal. A portion of the first open stub is provided in the first wiring layer, and the first open stub has one end coupled to the one end of the inductor and another open-circuited end. When the multilayer substrate is viewed in plan view in a stacking direction, a capacitor is formed by the first reference electrode and the first open stub that mutually overlap. A resonant circuit is formed by the capacitor and the inductor.

A filter circuit includes a pair of balanced input ports, a pair of balanced output ports, first and second resonators provided in parallel between the pair of balanced input ports and the pair of balanced output ports in a circuit configuration, a first capacitor connected in parallel to the first resonator, and a second capacitor connected in parallel to the second resonator. The first and second resonators are magnetically coupled to each other and electrically connected to each other. The first and second capacitors are not electrically connected to ground.

A diplexer includes a low-band band pass filter between a common input/output terminal and a low-band input/output terminal and a high-band band pass filter between the common input/output terminal and a high-band input/output terminal, wherein the low-band band pass filter includes LC resonators including a first-stage LC resonator to a final-stage LC resonator in order from the common input/output terminal toward the low-band input/output terminal, the high-band band pass filter includes LC resonators including a first-stage LC resonator to a final-stage LC resonator in order from the common input/output terminal toward the high-band input/output terminal, a matching capacitor is between the common input/output terminal and the low-band band pass filter, and the capacitance of a capacitor of the first-stage LC resonator of the low-band band pass filter is smaller than the capacitance of a capacitor of the final-stage LC resonator.

An LC resonator includes an external connection terminal, an inductor, a capacitor, and a via conductor pattern. The inductor winds around an axis orthogonal to a laminated direction. The capacitor is connected to the inductor. The via conductor pattern extends from the inductor in the laminated direction, and the inductor is connected to the external connection terminal with the via conductor pattern. The inductor includes a columnar conductor pattern extending in the X-axis direction. The area of the columnar conductor pattern in a plan view from the X-axis direction is greater than or equal to the area of the via conductor pattern in a plan view from the Z-axis direction.

The present disclosure provides a radio frequency duplexer circuit and a radio frequency substrate. The radio frequency duplexer circuit includes a first terminal, a second terminal, a third terminal, a low-pass filter, and a high-pass filter. The low-pass filter includes N first filter sub-circuits coupled in series and a first tuning sub-circuit. Among the N first filter sub-circuits coupled in series, a first end of a 1.sup.st first filter sub-circuit is coupled to the first terminal, and a second end of a N.sup.th first filter sub-circuit is coupled to the second terminal. The high-pass filter includes M second filter sub-circuits coupled in series and a second tuning sub-circuit. Among the M second filter sub-circuits coupled in series, a first end of a 1.sup.st second filter sub-circuit is coupled to the first terminal, and a second end of a M.sup.th second filter sub-circuit is coupled to the third terminal.

A low-pass filter includes first to third inductors and a capacitor. A first inductor-forming conductor layer constituting at least a part of each of the first and second inductors and a second inductor-forming conductor layer including first and second portions constituting first and second inductor portions of the third inductor are connected by a plurality of first through holes. The first portion and a capacitor-forming conductor layer constituting a part of the capacitor are connected by a plurality of second through holes. The second portion and the capacitor-forming conductor layer are connected by a plurality of third through holes.

Reversed semilattice filters with improved common mode rejection characteristics are disclosed. In one aspect, a filter may include two interior nodes coupled with an impedance that treats unwanted signals as common mode signals and provides rejection for common mode signals while passing differential signals of interest. The impedance is modified to have a resonant circuit that improves signal rejection in the stop band by lowering the effective impedance at those frequencies while leaving the pass band unaffected.

An electronic circuit includes a first filter and a second filter. The first filter passes a first frequency component of a first harmonic frequency generated by a first voltage source to form a potential difference in a chamber and a second frequency component of a second harmonic frequency higher than the first harmonic frequency. The second filter removes the first frequency component and the second frequency component received from the first filter. The second harmonic frequency is included in a first frequency band determined based on a capacitance of the second filter.

A low pass filter includes a first inductor, a second inductor magnetic-field-coupled to the first inductor, a third inductor, and a first capacitor. The first inductor is electrically connected between a first port and an intermediate node, being a node to which the second inductor is electrically connected, between the first inductor and the second port. The second inductor is electrically connected between the intermediate node and a ground terminal. The third inductor is electrically connected between the intermediate node and the second port, and a first parallel resonant circuit is defined by the third inductor and the first capacitor. The first inductor and the second inductor are coupled to each other in such a relationship that a negative inductance is generated between the intermediate node and the third inductor due to magnetic field coupling between the first inductor and the second inductor.

Embodiments of an apparatus that includes a substrate and an inductor residing in the substrate are disclosed. In one embodiment, the inductor is formed as a conductive path that extends from a first terminal to a second terminal. The conductive path has a shape corresponding to a two-dimensional (2D) lobe laid over a three-dimensional (3D) volume. Since the shape of the conductive path corresponds to the 2D lobe laid over a 3D volume, the magnetic field generated by the inductor has magnetic field lines that are predominately destructive outside the inductor and magnetic field lines that are predominately constructive inside the inductor. In this manner, the inductor can maintain a high quality (Q) factor while being placed close to other components.