A filter circuit that secures the steepness from a pass range to an attenuation range while maintaining a wide-band transmission characteristic and a filter device including this filter circuit are formed. A filter circuit includes a first filter and a second filter. The first filter is a filter including an LC circuit in which a first frequency band is a pass band and a frequency band not higher than the first frequency band is an attenuation band. The second filter is a filter that attenuates a second frequency band within the first frequency band by using an attenuation pole produced by a resonance or an antiresonance of an acoustic wave resonator. Further, the first filter is placed closer to an antenna terminal than the second filter.

Impedance matching circuit for radio-frequency amplifier. In some embodiments, an impedance matching circuit can include a primary metal trace having a first end configured to be capable of being coupled to a voltage source for the power amplifier, and a second end configured to be capable of being coupled to an output of the power amplifier. The impedance matching circuit can further include a secondary metal trace having first end coupled to the second end of the primary metal trace, and a second end configured to be capable of being coupled to an output node. The impedance matching circuit can further include a capacitance implemented between the first and second ends of the secondary metal trace, and be configured to trap a harmonic associated with an amplified signal at the output of the power amplifier.

An apparatus and method for a frequency based integrated circuit that selectively filters out unwanted bands or regions of interfering frequencies utilizing one or more tunable notch or bandpass filters or tunable low or high pass filters capable of operating across multiple frequencies and multiple bands in noisy RF environments. The tunable filters are fabricated within the same integrated circuit package as the associated frequency based circuitry, thus minimizing R, L, and C parasitic values, and also allowing residual and other parasitic impedance in the associated circuitry and IC package to be absorbed and compensated.

A method of constructing an RF filter comprises designing an RF filter that includes a plurality of resonant elements disposed, a plurality of non-resonant elements coupling the resonant elements together to form a stop band having a plurality of transmission zeroes corresponding to respective frequencies of the resonant elements, and a sub-band between the transmission zeroes. The non-resonant elements comprise a variable non-resonant element for selectively introducing a reflection zero within the stop band to create a pass band in the sub-band. The method further comprises changing the order in which the resonant elements are disposed along the signal transmission path to create a plurality of filter solutions, computing a performance parameter for each of the filter solutions, comparing the performance parameters to each other, selecting one of the filter solutions based on the comparison of the computed performance parameters, and constructing the RF filter using the selected filter solution.

A filter includes a body and first and second filters with pass bands different from each other. In the body, an inductor of the first filter is in a first range, and an inductor of the second filter is in a second range. The inductor in the first filter is a vertical coil including a plate electrode and a via extending in a normal direction of the body. In the second filter, the inductor facing the first range is a planar coil with a winding axis in the normal direction of the body. As seen in plan view in the normal direction of the body, an imaginary line from an extending-direction center of the plate electrode of the first filter in a direction perpendicular or substantially perpendicular to the extending direction does not intersect with the inductor of the second filter.

A branching filter includes a common port, a first signal port, a second signal port, a first filter, which is provided between the common port and the first signal port, that selectively passes a signal of a frequency within a first passband, a second filter, which is provided between the common port and the second signal port, that selectively passes a signal of a frequency within a second passband different from the first passband, and a capacitor that has a first end and a second end and connects the first filter and the second filter.

A transmission/reception module includes a substrate including a transmission signal input terminal, a reception signal output terminal, and an antenna terminal, an antenna switch circuit provided on the substrate and configured to output a transmission signal input from the transmission signal input terminal to the antenna terminal and configured to output a reception signal input from the antenna terminal to the reception signal output terminal, and a first inductor included in an input/output filter circuit provided between the antenna switch circuit and the antenna terminal. The first inductor includes a conductor whose winding axis direction is orthogonal to the substrate.

A coil component includes a first coil and a second coil that magnetically couples with the coil and causes a negative inductance to be generated. The coil component further includes an electrode that is provided at a position adjacent to or in the vicinity of a port of each of the first and second coils.

A filter includes a first capacitor connected in series between a first terminal pair and a second terminal pair, a first inductor connected in parallel with the first capacitor, and a second inductor connected in parallel between the first terminal pair and the second terminal pair. The first inductor and the second inductor are magnetically coupled to each other and are differentially connected to each other.

Systems and methods for tuning multiplexer filters are disclosed. In one aspect, a multiplexer includes a first filter coupled to a common node, the first filter configured to pass a first band, a second filter coupled to the common node, the second filter configured to pass a second band, and at least one electrical component configured to generate a notch at a frequency between the first band and the second band.