Radio frequency (RF) systems with tunable filters are provided herein. In certain embodiments, an RF system includes a first RF processing circuit configured to process a first frequency band of a first communication standard and a second frequency band of a second communication standard. The first frequency band and the second frequency band are close in frequency and/or partially overlapping in frequency. The first RF processing circuit includes a tunable filter for changing the bandwidth of the first RF processing circuit to enhance the robustness of the first RF processing circuit to blocker or jammer signals of a third frequency band.

A band pass filter includes: a resonator including a first inductor and a first capacitor coupled in series between a first port and a second port; a second capacitor coupled in parallel to the resonator; and a third capacitor connected between one end of the second capacitor and the ground to perform a low pass filter function.

A flexible multi-path RF adaptive tuning network switch architecture that counteracts impedance mismatch conditions arising from various combinations of coupled RF band filters, particularly in a Carrier Aggregation-based (CA) radio system. In one version, a digitally-controlled tunable matching network is coupled to a multi-path RF switch in order to provide adaptive impedance matching for various combinations of RF band filters. Optionally, some or all RF band filters include an associated digitally-controlled filter pre-match network to further improve impedance matching. In a second version, some or all RF band filters coupled to a multi-path RF switch include a digitally-controlled phase matching network to provide necessary per-band impedance matching. Optionally, a digitally-controlled tunable matching network may be included on the common port of the multi-path RF switch to provide additional impedance matching capability. In a third version, CA direct mapped adaptive tuning networks include filter tuning blocks for selected lower frequency bands.

A band-pass filter (BPF) includes first and second windings. The first winding includes first and second terminals, a first outer extending portion extending from the first terminal, a second outer extending portion extending from the second terminal, and a first conductive structure configured to electrically connect the first and second outer extending portions to each other at a location opposite the first and second terminals. The second winding includes third and fourth terminals positioned between the first and second terminals, and a second conductive structure electrically connected to the third and fourth terminals and extending between the first conductive structure and each of the first and second outer extending portions.

A filter device includes a common connection terminal, a first bandpass filter connected to the common connection terminal and including an inductor, and a second bandpass filter connected to the common connection terminal and having a pass band lower in frequency than a pass band of the first bandpass filter. The filter device uses SH waves. The first bandpass filter is a ladder filter. Each of series arm resonators and parallel arm resonators includes an interdigital transducer electrode. Of the parallel arm resonators of the first bandpass filter, the inductor is connected in series to the parallel arm resonator with a shortest electrode finger pitch of the interdigital transducer electrode.

A band-pass filter includes an unbalanced port, a first balanced port, a second balanced port, and first to third resonators provided between the unbalanced port and the first and second balanced ports. The second resonator and the third resonator each are a resonator with both ends open. The second resonator and the third resonator are adjacent to each other in a circuit configuration, and electromagnetically coupled by magnetic coupling as main coupling. The first resonator is provided closer to the second resonator than to the third resonator, and jump-coupled to the third resonator.

A filter circuit includes a pass band filter portion configured to pass signals in a first frequency spectrum and attenuate or block signals in a second frequency spectrum. The first frequency spectrum and the second frequency spectrum do not overlap. The pass band filter portion is configured to cause a return loss of more than 10 decibels (dB) in the first frequency spectrum.

An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3, and a dielectric film provided on the piezoelectric substrate to cover first and second IDT electrodes on the piezoelectric substrate. The first and second IDT electrodes include main electrode layers. When wave lengths determined by electrode finger pitches of the first and second IDT electrodes are λ.sub.1 and λ.sub.2, respectively, the average value thereof is λ.sub.0, λ.sub.1/λ.sub.0=1+X, and λ.sub.2/λ.sub.0=1−X, a relationship of 0.05≤X≤0.65 is satisfied. The wavelength λ.sub.1 is the longest, and the wavelength λ.sub.2 is the shortest. In Euler angles (φ, θ, ψ) of the piezoelectric substrate, φ is 0°±5°, ψ is 0°±10°, and θ satisfies Expression 1, wherein a relationship of B.sub.1<T×r≤0.10λ.sub.0 B.sub.2<T×r≤0.10λ.sub.0 are satisfied.

An oscillator includes a forward stage including first and second terminals and a transformer-coupled band-pass filter (BPF) coupled between the first and second terminals and including a coupling device between the first and second terminals, and a transformer including first and second windings in a metal layer of an IC. The first winding includes a first conductive structure coupled to the first terminal and a second conductive structure coupled to a voltage node, a third conductive structure including first and second extending portions connected to the first and second conductive structures. The second winding includes a fourth conductive structure including a third extending portion coupled to the voltage node, and a fourth extending portion coupled to the second terminal. The third extending portion is between the second conductive structure and the first extending portion, and the fourth extending portion is between the first conductive structure and the second extending portion.

A high frequency amplification circuit includes transmission amplification circuits 11 and 12; a transmission filter D-Tx whose pass band is a band D of a first frequency band group; transmission filters E-Tx and G-Tx whose pass bands are respectively bands E and G of a second frequency band group; an output matching circuit 31 configured to match the transmission amplification circuit 11 and the transmission filter D-Tx; and an output matching circuit 32 configured to match the transmission amplification circuit 12 and the transmission filters E-Tx and G-Tx. The band D is positioned at a high frequency-side end portion of the first frequency band group, and the band E is positioned at a low frequency-side end portion of the second frequency band group. The output matching circuit 31 includes a low-pass circuit, and the output matching circuit 32 includes an impedance-variable circuit.