In accordance with a first aspect of the present disclosure, an active RC-type filter is provided, comprising: an input, an output and a signal path between said input and output; at least one capacitor bank and at least one resistor bank, wherein said capacitor bank and resistor bank are integrated into the signal path; wherein the resistor bank comprises a plurality of resistor ladders; wherein each one of said resistor ladders comprises a plurality of resistors connected in series; wherein each one of said resistors has an input node configured to be coupled selectively to the signal path through one of a plurality of controllable switches; and wherein said resistor ladders have output nodes directly coupled to each other and to the signal path. In accordance with a second aspect of the present disclosure, a corresponding method of implementing an active RC-type filter is conceived.

A first attenuation circuit is connected between a node and ground, and the node is located between a ladder resonance circuit and a transmitter-side terminal. A second attenuation circuit is connected between a first parallel arm resonator of the ladder resonance circuit and ground and is connected in series to the first parallel arm resonator. The first attenuation circuit includes a second parallel arm resonator and a first switch that switches between a first state in which the second parallel arm resonator is connected to the node and a second state in which the first switch is open. The second attenuation circuit includes a capacitor and a second switch that switches between a first state in which the capacitor is connected to the first parallel arm resonator and a second state in which the first parallel arm resonator is connected to ground.

The present application provides a window function processing module including an integrating circuit, configured to receive an integrating input signal, the integrating circuit comprising an operational amplifier; an integrating capacitor, coupled to an output terminal and a first input terminal of the operational amplifier; and an adjustable impedance module, coupled between the first input terminal of the operational amplifier and an integrating input terminal of the integrating circuit, wherein the adjustable impedance module is controlled by at least one control signal to adjust an impedance value of the adjustable impedance module; and a control unit, coupled to the integrating circuit, configured to generate the at least one control signal according to a window function, to adjust the integration gain of the integrating circuit, such that the integrating output signal is related to an operation result of the integrating input signal and the window function.

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 high order filter circuit is integrated by a plurality of the low order filter circuits. Before correcting the high order filter circuit, switch units may restore the high order filter circuit to the low order filter circuits for correction, and then combine the corrected low order filter circuits to form the original high order filter circuit.

An acoustic wave filter device includes a ground connection terminal connected to an external ground electrode, a serial arm resonator, a first parallel arm circuit connected to a first node of the serial arm resonator, the first node being positioned closer to an input/output terminal, and to the ground connection terminal, and a second parallel arm circuit connected to a second node of the serial arm resonator, the second node being positioned closer to an input/output terminal, and to the ground connection terminal. The first parallel arm circuit includes a parallel arm resonator having a resonant frequency higher than a center frequency of a filter pass band, and a frequency varying circuit connected to the parallel arm resonator and the ground connection terminal. The second parallel arm circuit includes a parallel arm resonator having a resonant frequency higher than the center frequency of the filter pass band.

A filter device includes a filter (22A) connected to a common terminal (110) and having a first characteristic, a variable filter (22B) connected to the common terminal (110) and capable of changing a characteristic to one of a second characteristic and a third characteristic, and a switch (23). In the second characteristic, a second pass band including an overlapping band in which the second pass band and an attenuation band of the filter (22A) partially overlap in frequency is defined. Insertion loss within the overlapping band for the third characteristic is greater than insertion loss within the overlapping band for the second characteristic. When the filter (22A) is selected by the switch (23), the characteristic of the variable filter (22B) is set to the third characteristic.

Various embodiments of the invention relate to a high accuracy phase shift apparatus. The phase shift apparatus comprises a voltage controlled analog phase shifter, a microcontroller unit (MCU) and a digital-to-analog converter (DAC). The MCU generates a digital control signal, which is converted into an analog control signal by the DAC to control the voltage controlled analog phase shifter to achieve desired phase shift angle. The phase shift apparatus may further incorporate a temperature sensor for temperature compensation. The output from the temperature sensor may be used to modify the reference voltage of the DAC, or alternatively be used to modify the digital control signal from the MCU. By incorporation digitalized control and temperature compensation to an analog phase shifter, the disclosed phase shift apparatus achieves high accuracy digitalized control, a flat phase shift over a wide bandwidth, and a stable phase shift over temperature variation.

Methods and system for using a multifunctional filter to minimize insertion loss in a multi-mode communications system are described. Specifically described is a multifunctional filter that is configurable to operate in a band-pass mode when a first type of signal is propagated through the multifunctional filter, and to operate in a low-pass mode when a second type of signal is propagated through the multifunctional filter. The multifunctional filter presents a lower insertion loss to the second type of signal when operating in the low-pass mode than in the band-pass mode.

A filter device includes a terminal, a switch that includes a common terminal and selection terminals and switches a connection of the common terminal to one of the selection terminals, a series arm resonator, and filter circuits. The filter circuits are connected to one end of the series arm resonator. The common terminal is connected to the terminal. One of the selection terminals is connected between one end of the series arm resonator and the filter circuits. Another one of the selection terminals is connected to the other end of the series arm resonator.