A first series arm LC filter circuit includes a capacitor and an inductor connected in series to provide a series circuit between a first connection terminal and a second connection terminal, a capacitor connected in parallel to the series circuit, and an inductor and a variable capacitor connected in parallel between a connection point of the capacitor and the inductor and a ground potential. A first parallel arm LC filter circuit is connected between the first connection terminal and the ground potential. A second parallel arm LC filter circuit is connected between the second connection terminal and the ground potential. The inductor is directly connected to the second connection terminal or is connected to the second connection terminal with another inductor interposed therebetween.

An integrated circuit (IC) includes an input pad and an output pad separated from the input pad by a predetermined distance. A plurality of capacitors are coupled in series between the input pad and the output pad. The plurality of capacitors are distributed to substantially span the predetermined distance. An inductor is formed from a bond wire, having a first end attached at the first input pad and a second end attached at the output pad. The inductor and plurality of capacitors configured to form a predetermined open circuit resonance.

An LC parallel resonator includes a plurality of dielectric layers stacked on top of one another, a capacitor electrode, and an inductor electrode. The inductor electrode defines a loop including a connection point, as a start point, connected to the capacitor electrode. The inductor electrode includes a first line electrode, first via electrodes, and second via electrodes. The first line electrode extends in a direction perpendicular or substantially perpendicular to a stacking direction of the dielectric layers. The first via electrodes arranged in parallel or substantially in parallel with one another extend in the stacking direction of the dielectric layers, and connect the capacitor electrode to the first line electrode. The second via electrodes arranged in parallel or substantially in parallel with one another extend in the stacking direction of the dielectric layers and are connected to the first line electrode.

The present disclosure includes a first circuit that is connected between a power feed port and an antenna port, and a second circuit that is connected between the power feed port and the ground or between the antenna port and the ground. The first circuit is a circuit in which for example a first variable capacitance element is connected in series with a first inductor, and the second circuit is a circuit in which for example a second variable capacitance element is connected in parallel with a second inductor. A switch performs switching at least between a first state in which a second end of the second circuit is connected to a first end of the first circuit and a second state in which the second end of the second circuit is connected to a second end of the first circuit.

An elliptic combiner circuit filters a first and second signal in a first and second frequency band. A first resonator is coupled to a first input via a first capacitor and a second input via a second capacitor. A second resonator is coupled to a first and second signal path, coupled to the first and second input, via a third and a fourth capacitor. A first inductor is coupled between the first and third capacitors, and between the second and fourth capacitors. A third resonator is coupled to the first and second signal paths via a fifth, sixth, and seventh capacitors. A fourth resonator is coupled to the first signal path and a terminated port via an eighth, ninth and tenth capacitors. A second inductor is coupled between the fifth and eighth capacitors, and between the seventh and tenth capacitors. An output outputs the first and second signals.

An impedance-matching circuit includes a resonant circuit, first and second capacitors, and first through third inductive circuits. The resonant circuit includes a fourth inductive circuit connected in parallel with a capacitive circuit. The impedance-matching circuit receives a radio frequency power amplifier (RFPA) output signal, which includes first and second signals at first and second frequencies, respectively. A resonant frequency of the resonant circuit is between the first and second frequencies. The resonant circuit offers inductive and capacitive impedances to the first and second signals, respectively. The impedance-matching circuit generates a matched RFPA output signal including the first signal and the second signal, where the second signal is at a reduced voltage level.

A method of designing a multiple-tuned filter (MTF) of a high voltage direct current (HVDC) system is provided. The method includes selecting an input parameter for the MTF, setting a resonance frequency of the MTF, calculating values of inductance (L) and capacitance (C) which are filter parameters of the MTF on the basis of the input parameter and the resonance frequency, combining a value of resistance (R) with the filter parameters and calculating a price according to the combination, and storing the combined values of R, L, and C when the calculated price falls within a predetermined price range.

Radio frequency (RF) filters configured to filter undesired signal components (e.g., noise and harmonics) from RF signals are disclosed. In one embodiment, an RF filter includes a first inductor coil having a first winding and a second inductor coil having a second winding and a third winding. The second winding of the second inductor coil is configured to have a first mutual magnetic coupling with the first winding, while the third winding of the second inductor coil is configured to have a second mutual magnetic coupling with the first winding. The second winding is connected to the third winding such that the first mutual magnetic coupling and the second mutual magnetic coupling are in opposition. In this manner, the first inductor coil and the second inductor coil may be provided in a compact arrangement while providing weak mutual magnetic coupling between the first inductor coil and the second inductor coil.

A radio frequency (RF) receiver, which has an RF filter and impedance matching circuit and an RF low noise amplifier (LNA), is disclosed. The RF filter and impedance matching circuit includes a first passive RF acoustic resonator; provides an RF bandpass filter having an RF receive band based on the first passive RF acoustic resonator; and presents an input impedance at an RF input and an output impedance at an RF output, such that a ratio of the output impedance to the input impedance is greater than 40. The RF LNA is coupled to the RF output.

Methods and apparatus, including computer program products, are provided filters. In some example embodiments, there is provided a radio frequency filter including at least one resonant circuit selectable to vary at least the selectivity of the radio frequency filter, wherein the selectivity is varied based on at least one of a first amount of transmit power being used at a user equipment and a second amount of received signal power. Related apparatus, systems, methods, and articles are also described.