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.

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 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 band pass filter includes parallel resonators. An inductor of a first parallel resonator at an intermediate stage is divided into a first inductor and a second inductor connected in parallel with each other. The first inductor and an inductor of a second parallel resonator are in magnetic coupling with each other, and the second inductor and an inductor of a third parallel resonator are in magnetic coupling with each other.

A band pass filter includes parallel resonators. An inductor of a first parallel resonator at an intermediate stage is divided into a first inductor and a second inductor connected in parallel with each other. The first inductor and an inductor of a second parallel resonator are in magnetic coupling with each other, and the second inductor and an inductor of a third parallel resonator are in magnetic coupling with each other.

An electronic component includes a second inductor including a second inductor conductor that includes a first coupling portion electrically coupled to a second capacitor conductor and a second coupling portion electrically coupled to a second ground conductor, and when viewed in a plan view from a lamination direction, a first region surrounded by a first inductor conductor and the second inductor conductor is smaller in area than a second region surrounded by a third inductor conductor layer and the second inductor conductor, and a second region forming portion, which is included in the second inductor conductor and surrounds the second region, and a first region forming portion, which is included in the second inductor conductor and surrounds the first region, are electrically coupled in series in this order on a path from the first coupling portion to the second coupling portion.

An electronic component includes a second inductor including a second inductor conductor that includes a first coupling portion electrically coupled to a second capacitor conductor and a second coupling portion electrically coupled to a second ground conductor, and when viewed in a plan view from a lamination direction, a first region surrounded by a first inductor conductor and the second inductor conductor is smaller in area than a second region surrounded by a third inductor conductor layer and the second inductor conductor, and a second region forming portion, which is included in the second inductor conductor and surrounds the second region, and a first region forming portion, which is included in the second inductor conductor and surrounds the first region, are electrically coupled in series in this order on a path from the first coupling portion to the second coupling portion.

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 low pass filter includes a first input/output terminal, a second input/output terminal, a signal line, inductors connected in the signal line, and capacitors connected between the signal line and ground. In the signal line, a capacitor is connected in parallel to the inductor that is connected closest to the first input/output terminal, and the inductor and the capacitor define a first parallel resonator.

An electronic component includes: a conductive pattern provided on the main surface of a substrate and constituting a lower electrode; a dielectric film that covers top and side surfaces of the conductive pattern; and a conductive pattern stacked on the top surface of the conductive pattern through the dielectric film and constituting an upper electrode. A part of the dielectric film that is parallel to the main surface of the substrate is removed at least partly. Partially removing a part of the dielectric film that is parallel to the main surface of the substrate allows stress relaxation. This prevents peeling at the interface between the lower electrode and the dielectric film.