A tunable filter using acoustic resonators is disclosed. A tunable filter includes a plurality of tunable resonator units (20). Each tunable resonator unit (20) has acoustic wave resonators (12). Each acoustic wave resonator is associated with a different tunable frequency. Each tunable resonator unit also has a first switch (22) configured to select one of the plurality of acoustic wave resonators of the tunable resonator unit at a time. The first switches of the plurality of tunable resonator units are coupled to cooperatively select one acoustic wave resonator in each one of the plurality of tunable resonator units, where a selected acoustic wave resonator in a tunable resonator unit of the plurality of tunable acoustic resonator units is associated with a same tunable frequency response as the other selected acoustic resonators of the others of the plurality of tunable acoustic resonator units. The selection results in an overall tunable frequency response.

The acoustic wave filter (10A) includes a parallel-arm resonant circuit (12p). The parallel-arm resonant circuit (12p) includes a parallel-arm resonator (p1) and a frequency variable circuit (72p) that are connected in parallel. The frequency variable circuit (72p) includes a parallel-arm resonator (p2) that has a resonant frequency higher than that of the parallel-arm resonator (p1) and a switch (SW1) element. A frequency difference between a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is OFF and a resonant frequency on a higher frequency side of the parallel-arm resonant circuit (12p) in a case where the switch (SW1) is ON is equal to or more than a frequency difference between a low frequency end frequency of the second attenuation band and a low frequency end frequency of the first attenuation band.

A variable filter includes a serial arm resonator and a parallel arm resonance circuit, the parallel arm resonance circuit includes a parallel arm resonator and a capacitance element connected to the parallel arm resonator, the serial arm resonator and the parallel arm resonator respectively include IDT electrodes each formed of a plurality of electrode fingers formed on a substrate, and a film thickness of the plurality of electrode fingers of the parallel arm resonator is larger than a film thickness of the plurality of electrode fingers of the serial arm resonator.

RF communications circuitry, which includes a first tunable RF filter and a first RF low noise amplifier (LNA) is disclosed. The first tunable RF filter includes a pair of weakly coupled resonators, and receives and filters a first upstream RF signal to provide a first filtered RF signal. The first RF LNA is coupled to the first tunable RF filter, and receives and amplifies an RF input signal to provide an RF output signal.

A tunable filter is provided. The tunable filter includes: a filter input; a filter output; at least one feedback loop coupled between the filter output and the filter input, where the at least one feedback loop includes at least one tunable feedback capacitance which is configured to tune a cut-off frequency of the tunable filter; and an active element, coupled between the filter input and the filter output and configured to drive the at least one tunable feedback capacitance, the active element having a transfer function with a primary pole and at least one secondary pole, where the active element includes a first stabilization element that is coupled to a first internal node of the active element.

A re-configurable magnetoinductive waveguide (300), comprising a plurality of resonator cells, wherein each resonator cell comprises a primary resonator (110) that is inductively coupled to a primary resonator (110) of at least one other resonator cell, and wherein at least one of the plurality of resonator cells is a controllable cell (100) which further comprises a control element (120), the control element (120) having an active control component (125) that is operable to adjust the impedance of the primary resonator (110) of the controllable cell (100) in response to a control signal; wherein: the control element (120) comprises a secondary resonator, the secondary resonator is inductively coupled to the primary resonator (110), and the active control component (125) is arranged to vary the electrical properties of the secondary resonator in response to the control signal.

A variable filter and method of switching a resonant frequency of the variable filter from an initial frequency to a desired frequency, where the variable filter has a tunable frequency and a variable Q. With the variable filter operating at the initial frequency and an initial Q, the variable filter is Q-spoiled toward a low-Q state. The variable filter is tuned toward the desired frequency and the tunable resonator is Q-enhanced from the low-Q state to achieve a desired filter response.

Systems, devices, and methods for tunable filters that are configured to support multiple frequency bands, such as within the field of cellular radio communication, can include a first resonator and a second resonator configured to block signals within one or more frequency ranges, and one or more coupling element connected to both the first resonator and the second resonator. The one or more coupling element can be configured to provide low insertion loss within a pass band.

Various embodiments relate to a method for calibration of a center frequency of a BPF in an FSK transceiver, the method including the steps of filtering a carrier frequency signal by the BPF to produce a filtered signal, detecting, by a phase-frequency detector (PFD), a difference in phase between the carrier frequency signal and the filtered signal from the BPF, sweeping a calibration code of the BPF, detecting a transition in the sign of the phase difference and capturing a calibration code associated with the transition in the sign of the phase difference for calibration of the BPF.

A variable filter has a signal loop defined between a signal input and a signal output. A plurality of circuit elements connected in the signal loop, the plurality of circuit elements comprising a frequency tunable resonator, and an adjustable scaling block that applies a gain factor that is adjustable in a range that comprises a positive gain and a negative gain. A controller is connected to 1) tune the frequency tunable resonator; and to 2) adjust the gain factor of the adjustable scaling block between a negative gain factor to a positive gain factor providing for variable Q independent of frequency.