An adjustable inductor including a toroidal core defining a plurality of gaps, a compressible gap material positioned in the gaps, at least one winding wound on the core, a force-applying structure, and a film substantially covering the adjustable inductor. The force-applying structure is operable to apply a force to the core to adjust the gaps and thereby an inductance of the adjustable inductor. The film is configured to prevent movement of force-applying structure when above a predetermined temperature threshold, and allow movement of the force-applying structure when below the predetermined threshold.

In a first approach, a reconfigurable radio frequency (RF) filtering module includes a phase-change material (PCM) RF switch bank and an RF filter bank. Each RF filter in the RF filter bank is capable to be engaged and disengaged by a PCM RF switch in the PCM RF switch bank. In a second approach, a tunable RF filter includes PCM RF switches and a capacitor and/or an inductor. Each of the capacitor and/or inductor is capable to be engaged and disengaged by at least one PCM RF switch of the PCM RF switches. In a third approach, an adjustable passive component includes multiple segments and a PCM RF switch. A selectable segment in the multiple segments is capable to be engaged and disengaged by the PCM RF switch. In all approaches, each PCM RF switch includes a PCM and a heating element transverse to the PCM.

A variable frequency filter includes a series arm resonant circuit and first and second parallel arm resonant circuits. The series arm resonant circuit is connected between a first connection terminal and a second connection terminal. The first parallel arm resonant circuit is connected to the first connection terminal side of the series arm resonant circuit. In the first parallel arm resonant circuit, a first piezoelectric resonator and a variable capacitor are connected in series to each other. The second parallel arm resonant circuit is connected to the second connection terminal side of the series arm resonant circuit. In the second parallel arm resonant circuit, a second piezoelectric resonator and a variable capacitor are connected in series to each other. The impedance of the first piezoelectric resonator is lower than the impedance of the second piezoelectric resonator. The series arm resonant circuit includes a characteristic adjusting capacitor at the first connection terminal side.

A high-order filter with a capacitive inner tapping technique is disclosed. The filter includes an inductor and a first resonant circuit including a first portion of the inductor and a first capacitor. The first resonant circuit is configured to attenuate first frequency components of an input signal above a cutoff frequency to generate a filtered signal. The filter further includes a second resonant circuit coupled in parallel with the first resonant circuit and including the first portion of the inductor and a second capacitor. The second resonant circuit is configured to attenuate the first frequency components of the input signal to generate the filtered signal. A third resonant circuit includes a second portion of the inductor and a third capacitor, wherein the third resonant circuit is configured to attenuate second frequency components of the filtered signal above the cutoff frequency to generate an output signal.

A tunable inductor circuit includes a first common transmission line having one end connected to a first terminal; a first uncommon transmission line having one end connected to another end of the first common transmission line; a first switch circuit configured to selectively connect one of the other end of the first common transmission line and another end of the first uncommon transmission line to a first common node; a second common transmission line having one end connected to the first common node; a second uncommon transmission line having one end connected to another end of the second common transmission line; and a second switch circuit configured to selectively connect one of the other end of the second common transmission line and another end of the second uncommon transmission line to a second terminal.

A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) includes a series arm resonator (s1a) and a variable frequency circuit (11b) connected in parallel with the series arm resonator (s1a). The variable frequency circuit (11b) includes a series arm resonator (s1b) and a switch (SWb) connected in series with the series arm resonator (s1b). The variable frequency circuit (11b) is configured to change at least one of a resonant frequency that provides a pass band of the radio-frequency filter (10) and an anti-resonant frequency that provides an attenuation pole of the radio-frequency filter (10). A resonant frequency of the series arm resonator (s1b) is different from a resonant frequency of the series arm resonator (s1a).

A filter includes a longitudinally coupled resonator device, a parallel arm resonator, and a variable frequency circuit. The parallel arm resonator is connected between a ground and a node provided on a path connecting input-output terminals. The variable frequency circuit is connected to the first parallel arm resonator. The longitudinally coupled resonator device includes three or more odd-number IDT electrodes, an odd-numbered IDT terminal, and an even-numbered IDT terminal. The even-numbered IDT terminal is a first signal terminal connected to at least one IDT electrode located at an even-numbered position from an edge of an arrangement order of the plural IDT electrodes. The odd-numbered IDT terminal is a second signal terminal connected to two or more IDT electrodes located at odd-numbered positions from the edge. The longitudinally coupled resonator device is disposed so that the even-numbered IDT terminal is connected to the node.

A notch filter includes an inductor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second or third resonator or both. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.

In accordance with an embodiment, an RF system includes a transmit path having a first tunable transmit band stop filter, and a power amplifier coupled to an output of the first tunable transmit band stop filter, where the first tunable transmit band stop filter is configured reject a receive frequency and pass a transmit frequency; a receive path comprising an LNA; and a duplex filter having a transmit path port coupled to an output of the power amplifier, a receive path port coupled to an input of the LNA, and an antenna port, where the duplex filter is configured to pass the transmit frequency and reject the receive frequency between the antenna port and the transmit path port, pass the receive frequency and reject the transmit frequency between the antenna port and the receive path port.