A high-frequency filter includes a variable frequency filter, a fixed frequency filter, and switches. The variable frequency filter varies a passband in association with frequencies used in multiple communication band. The fixed frequency filter fixes a passband in association with a frequency used in a specific communication band different from the multiple communication bands. The switches are used to switch connection configuration to the variable frequency filter or the fixed frequency filter.

Radio frequency (RF) filter structures and related methods and RF front-end circuitry are disclosed. In one embodiment, an RF filter structure includes a first terminal and a first tunable RF filter path defined between the first terminal and a second terminal. The first tunable RF filter path is tunable to provide impedance matching between the first terminal and the second terminal at a first frequency. The first frequency may be provided within a first frequency band. Additionally, the RF filter structure includes a second tunable RF filter path defined between the first terminal and the second terminal. The second tunable RF filter path is tunable to provide impedance matching between the first terminal and the second terminal at a second frequency. The second frequency may be within a second frequency band. In this manner, the RF filter structure is configured to provide impedance tuning for multiple impedance bands simultaneously.

An interdigitated RF filter. The interdigitated RF filter includes input fingers connected to an input node and output fingers connected to an output node where at least one input finger is connected the output node or at least one output finger is connected to the input node. The described interdigitated RF filter can be implemented in various configurations such as series, shunt, ladder or a combination thereof.

Methods, apparatus, systems, and articles of manufacture are described corresponding to current limit circuitry with controlled current variation. An example circuit includes an amplifier having an input terminal and an output terminal; a capacitor having a first terminal and a second terminal, the first terminal of the capacitor coupled to the input terminal of the amplifier, the second terminal of the capacitor coupled to the output terminal of the amplifier; and diode circuitry having a first terminal and a second terminal, the first terminal of the diode circuitry coupled to the first terminal of the capacitor and the input terminal of the amplifier, the second terminal of the diode circuitry coupled to the second terminal of the capacitor and the output terminal of the amplifier.

A voltage-controlled oscillator (VCO) includes a power supply source, a voltage source, a reference voltage node, first and second transistors, each including a source terminal coupled to the reference voltage node, and first through fourth conductive structures. The first conductive structure includes a first terminal coupled to the power supply source, a first extending portion coupled between the first terminal and a drain terminal of the first transistor, and a second extending portion coupled between the first terminal and a drain terminal of the second transistor, and the second conductive structure includes a second terminal coupled to the voltage source, a third extending portion coupled in series with the third conductive structure between the second terminal and a gate of the first transistor, and a fourth extending portion coupled in series with the fourth conductive structure between the second terminal and a gate of the second transistor.

An LC filter includes an input terminal, an output terminal, a multilayer body, plate electrodes, connection electrodes connecting the plate electrodes, capacitor electrodes, and a inductor vias. Each of the capacitor electrodes opposes the plate electrode. One end of an inductor via is connected with the input terminal with a capacitor electrode interposed therebetween. Another end of the inductor via is connected to an intermediate point of a connection electrode. An inductor via is connected between the plate electrode and a capacitor electrode. An inductor via is connected between the plate electrode and a capacitor electrode. One end of an inductor via is connected with the output terminal with a capacitor electrode interposed therebetween. Another end of the inductor via is connected to an intermediate point of a connection electrode.

Radio frequency (RF) front-end circuitry that includes control circuitry and an RF filter structure that includes a plurality of resonators are disclosed. In one embodiment, a first tunable RF filter path is defined by a first set of the plurality of resonators such that the first tunable RF filter path has a first amplitude and a first phase. A second tunable RF filter path is defined by a second set of the plurality of resonators such that the second tunable RF filter path has a second amplitude and a second phase. To provide antenna diversity and/or beam forming/beam steering, the control circuitry is configured to set a first amplitude difference between the first amplitude and the second amplitude to approximately a first target amplitude difference and set a first phase difference between the first phase and the second phase to approximately a first target phase difference.

A high frequency band pass filter with a coupled surface mount transition is provided, including a filter substrate, circuit connection elements defining input and an output elements provided on a surface of the filter substrate, electronic filter components provided on the first surface of the filter substrate, and impedance matching structures provided on the first surface of the filter substrate between the electronic filter components and the respective input and output elements. Signal connection structures are provided on an opposed surface of the filter substrate, in locations that positionally correspond to respective positions of the input and output elements. The respective signal connection elements are capacitively coupled, through a thickness direction of the filter substrate, to a respective one of the input and output elements on the opposed surface of the filter substrate without the presence of any vertical conductive structures within the filter substrate at the input and the output elements.

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 very wide bandwidth composite band pass filter with steep roll-off of a corresponding passband includes a band pass filter and a high-Q acoustic resonator. The band pass filter has a corresponding passband with a very wide bandwidth and a passband roll-off. The high-Q acoustic filter has a corresponding stopband with a roll-off steeper than the passband roll-off, the high-Q acoustic filter being connected in parallel with the band pass filter such that a portion of the stopband is within the passband of the band pass filter, forming a combined passband. A frequency range of the combined passband is approximately the same as a frequency range of the passband of the band pass filter, and a combined roll-off of the combined passband is steeper on one side than the passband roll-off of the band pass filter.