In tuning a radio frequency (RF) module including a non-volatile tunable RF filter, a desired frequency and an undesired frequency being provided by an amplifier of the RF module are detected. The non-volatile tunable RF filter is coupled to an output of the amplifier of the RF module. A factory setting of an adjustable capacitor in the non-volatile tunable RF filter is changed by factory-setting a state of a non-volatile RF switch, such that the non-volatile tunable RF filter substantially rejects the undesired frequency and substantially passes the desired frequency. The adjustable capacitor includes the non-volatile RF switch, and the factory setting of the adjustable capacitor corresponds to a factory-set state of the non-volatile RF switch. An end-user is prevented access to the non-volatile RF switch, so as prevent the end-user from modifying the factory-set state of the non-volatile RF switch.

A multiplexer capable of concurrently sending a radio-frequency signal in one of Band A and Band B belong to a low band group and a radio-frequency signal in a Band C belongs to a high band group that includes: a common terminal and input/output terminals; a low-pass filter arranged between the common terminal and the input/output terminal and whose pass band is frequencies in the low band group and whose attenuation band is frequencies in the high band group; and a high-pass filter arranged between the common terminal and the input/output terminal and whose pass band is the frequencies in the high band group and whose attenuation band is the frequencies in the low band group. The low-pass filter includes a first frequency-variable circuit including a switch, and at least one of the pass band and the attenuation band of the low-pass filter is changeable.

A directional coupler includes a main line for transmitting a high frequency signal, a sub line electromagnetically coupled to the main line, a termination circuit for terminating one end portion of the sub line, and a variable filter that has an input terminal and an output terminal and the input terminal is connected to another end portion of the sub line. The variable filter is a filter unit circuit having one frequency band as a pass band or a stop band, and in the filter unit circuit, a variable passive element for shifting a frequency in the pass band or the stop band is disposed.

A filter can perform two filtering processes. The filter includes a switching circuit, a first filter circuit, and a second filter circuit. The first filter circuit is coupled to the switching circuit. The second filter circuit is coupled to the switching circuit. The first filter circuit performs a first filtering process on an input signal according to a state of the switching circuit. The first filter circuit and the second filter circuit work together to perform a second filtering process on the input signal according to the state of the switching circuit.

A multi-tune filter system and a control system for operating the multi-tune filter system are described herein. The multi-tune filter system is a tunable frequency range filter. Further, the multi-tune filter system is a digitally programmable filter with an adjustable passband between first and second customizable frequency bounds f1, f2.

Digital step attenuator (DSA) and digital phase shifter (DPS) multi-stage circuit architectures that provide for high resolution. Embodiments use a dithering approach to weight bit positions to provide a much finer resolution than the lowest-valued individual stage. Bit position weights for stages are determined so as to enable selection of combinations of n bit positions that provide a desired total attenuation or phase shift range while allowing utilization of the large number of states (2.sup.n) available to produce fractional intermediate steps of attenuation or phase shift. The fractional intermediate steps have a resolution finer than the lowest-valued stage. Bit position weights may be determined using a weighting function, including weightings determined from a linear series, a geometric series, a harmonic series, or alternating variants of such series. In some embodiments, at least one bit position has a fixed value that is not determined by the bit position weighting function.

A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) is disposed on a path connecting an input/output terminal (11m) and an input/output terminal (11n). The parallel arm circuit (12) is connected to a ground and to a node (x1) on the path. The series arm circuit (11) includes a series connecting circuit (11e) and a first variable frequency circuit (11a). The series connecting circuit (11e) includes a series arm resonator (s1) and a capacitor (C1). The first variable frequency circuit (11a) is connected in parallel with the series connecting circuit (11e) and varies the anti-resonant frequency of the series arm circuit (11). The first variable frequency circuit (11a) includes a capacitor (C2) and a switch (SW1) connected in series with each other. The series arm resonator (s1) and the capacitor (C1) are connected in series with each other.

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.

Embodiments of resonator circuits and modulating resonators and are described generally herein. One or more acoustic wave resonators may be coupled in series or parallel to generate tunable filters. One or more acoustic wave resonances may be modulated by one or more capacitors or tunable capacitors. One or more acoustic wave modules may also be switchable in a filter. Other embodiments may be described and claimed.

A filter includes a switching circuit, a first filter circuit, and a second filter circuit. The first filter circuit is coupled to the switching circuit. The second filter circuit is coupled to the switching circuit. The switching circuit is controlled to control the first filter circuit to perform a first filtering process on an input signal or control the first filter circuit to work in coordination with the second filter circuit to perform a second filtering process on the input signal.