A variable-frequency LC filter (1A) includes a multilayer circuit board, a series arm capacitor (11) formed in the multilayer circuit board and disposed in a series arm path that connects an input electrode to an output electrode, and a parallel arm inductor (21) formed in the multilayer circuit board and disposed in a parallel arm path that connects a ground electrode to a node (N1) in the series arm path. When the multilayer circuit board is viewed in plan, of the series arm capacitor (11) and the parallel arm inductor (21), only the parallel arm inductor (21) overlaps with the ground electrode.

A low-pass filter having a notch frequency due to a resonance between a mutual inductance of inductive elements and a capacitance. An exemplary low-pass filter generally includes a first inductive element having a first terminal and a second terminal, the first terminal being coupled to the input port, and a second inductive element having a first terminal and a second terminal, the first terminal of the second inductive element being coupled to the second terminal of the first inductive element and the second terminal of the second inductive element being coupled to the output port. The filter also includes a shunt capacitive element coupled to the second terminal of the first inductive element, wherein a mutual inductance between the first inductive element and the second inductive element and a capacitance of the shunt capacitive element are configured to have a resonance providing a notch frequency for the low-pass filter.

A tunable filter is described where the frequency response as well as bandwidth and transmission loss characteristics can be dynamically altered, providing improved performance for transceiver front-end tuning applications. The rate of roll-off of the frequency response can be adjusted to improve performance when used in duplexer applications. The tunable filter topology is applicable for both transmit and receive circuits. A method is described where the filter characteristics are adjusted to account for and compensate for the frequency response of the antenna used in a communication system.

A system for thermally protecting an amplifier driving a capacitive load may include a low-pass filter configured to filter, with a variable cutoff frequency, an input signal to generate a filtered input signal, wherein the amplifier is configured to receive the filtered input signal and amplify the filtered input signal to generate a driving signal to the capacitive load and a controller configured to receive a real-time estimate of a temperature associated with the amplifier and vary the variable cutoff frequency as a function of the temperature.

A low-pass filter having a notch frequency due to a resonance between a mutual inductance of inductive elements and a capacitance. An exemplary low-pass filter generally includes a first inductive element having a first terminal and a second terminal, the first terminal being coupled to the input port, and a second inductive element having a first terminal and a second terminal, the first terminal of the second inductive element being coupled to the second terminal of the first inductive element and the second terminal of the second inductive element being coupled to the output port. The filter also includes a shunt capacitive element coupled to the second terminal of the first inductive element, wherein a mutual inductance between the first inductive element and the second inductive element and a capacitance of the shunt capacitive element are configured to have a resonance providing a notch frequency for the low-pass filter.

A method for the batch production of acoustic wave filters comprises: synthesizing N theoretical filters, each filter defined by a set of j theoretical resonator(s) having a triplet C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq, these parameters grouped into subsets; determining a reference resonator structure for each subset, naturally having a resonant frequency .sub.r,ref, where .sub.aij,eq<.sub.r,ref<.sub.rij,eq; determining, for each theoretical resonator, an elementary building block comprising an intermediate resonator R.sub.ij, a parallel reactance Xp.sub.ij and/or a series reactance Xs.sub.ij, the intermediate resonator R.sub.ij having a triplet C.sub.0ij, .sub.r,ref and .sub.a,ref, the parameters C.sub.0ij, Xpij and/or Xs.sub.ij defined so the elementary building block has a triplet: C.sub.0ij,eq, .sub.rij,eq and .sub.aij,eq; determining the geometrical dimensions of the actual resonators R.sub.ij of the filters so they have a capacitance C.sub.0ij; producing each actual resonator; associating series and/or parallel reactances with actual resonators in order to form the elementary building blocks.

Systems and methods for converting a capacitance signal into a band-limited voltage signal for improved signal processing are disclosed herein. Such systems can include a capacitance-to-voltage converter configured to convert a capacitive signal from a capacitive device that operates at a mechanical frequency into a raw voltage signal, a clock generator configured to convert the mechanical frequency into one or more clock signals, and a filter component configured to apply a band-pass filter response to the raw voltage signal to convert the raw voltage signal into a band-limited voltage signal. The clock generator can be configured to apply the one or more clock signals to the filter component to drive a first pole and a second pole of the band-pass filter response to track the mechanical frequency of the capacitive device such that the geometric mean of the first pole and the second pole is substantially equal to the mechanical frequency.

An audio filter and corresponding method with through-zero linearly variable resonant frequency are described. An example method includes receiving an input signal; receiving one or more control input signals; and providing a resonant filter for electronic music for processing the input signal. The resonant filter can include an exponential times linear multiplication to produce the resonant frequency control responsive to control voltages exponentially for musical octave/semitone control, and linearly for timbre modulation, the waveform being invariant over corresponding exponential changes in pitch of both input signal and filter resonance. The linear modulation can include inverting the sign of a bandpass feedback based on the sign of the resonant frequency variable so as to maintain stability. In the example method, to prevent a glitch on the output when frequency changes sign, a separate highpass output signal may be generated.

An acoustic impedance transformation circuit and related apparatus are provided. In aspects discussed herein, the acoustic impedance transformation circuit can be configured to transform an input impedance into an output impedance higher than the input impedance. In this regard, the acoustic impedance transformation circuit can be provided in an apparatus to enable impedance matching between two electrical circuits. As a result, it may be possible to reduce signal reflection resulting from impedance mismatch between the two circuits, thus helping to improve performance of the apparatus.

A method and apparatus for modifying or controlling a resonator connected to a signal loop having an input (18828), an output (18822), and a closed loop frequency response. The signal loop has a primary resonator (18810) having a primary frequency response. There is at least one adjustable resonator (18812) having an adjustable frequency (f) and a secondary Q-factor. An adjustable scaling block (18824) applies a gain factor (g). A controller is connected to the at least one adjustable resonator (18812) and the adjustable scaling block (18824). The controller has instructions to adjust the closed loop frequency response toward a desired closed loop frequency response by controlling the adjustable frequency (f) of the at least one adjustable resonator (18812) and the gain factor (g) of the adjustable scaling block (18824).