A resonator element for use in a filter is provided. The resonator element includes a first resonator acoustically coupled to a second or third resonator or both. The first resonator has terminals for incorporation in a filter structure. A tuning circuit is coupled to the second or third resonator or both to enable tuning of the resonator element. The tuning circuit includes a variable capacitor and an inductor.

A variable filter and method of switching a resonant frequency of the variable filter from an initial frequency to a desired frequency, where the variable filter has a tunable frequency and a variable Q. With the variable filter operating at the initial frequency and an initial Q, the variable filter is Q-spoiled toward a low-Q state. The variable filter is tuned toward the desired frequency and the tunable resonator is Q-enhanced from the low-Q state to achieve a desired filter response.

Embodiments of oscillator circuits for wireless transmission of data are disclosed herein. In one example, an oscillator circuit includes an active network and a passive differential network coupled to the active network is disclosed. The active network is configured to generate an active signal for sustaining oscillation of the oscillator circuit. The passive network includes a first subnetwork, a second subnetwork, a first inductor and a second inductor. The first subnetwork is configured to adjust a central value of a resonant frequency of the oscillation. The passive network further includes a second subnetwork configured to further adjust the resonant frequency of the oscillation.

Embodiments of oscillator circuits for wireless transmission of data are disclosed herein. In one example, an oscillator circuit includes an active network and a passive differential network coupled to the active network is disclosed. The active network is configured to generate an active signal for sustaining oscillation of the oscillator circuit. The passive network includes a first subnetwork, a second subnetwork, a first inductor and a second inductor. The first subnetwork is configured to adjust a central value of a resonant frequency of the oscillation. The passive network further includes a second subnetwork configured to further adjust the resonant frequency of the oscillation.

In accordance with an embodiment, a method of operating an RF system includes filtering a first wideband RF signal using a wideband filter bank. Filtering the first RF signal includes separating the first wideband RF signal into frequency cluster signals, where each frequency cluster signal of the frequency cluster signals includes different frequency ranges, the first wideband RF signal includes multiple RF bands, and each of the different frequency ranges comprises a plurality of RF bands of the multiple RF bands. The method further includes band stop filtering at least one of the frequency cluster signals to produce a band stopped frequency cluster signal.

In accordance with an embodiment, a method of operating an RF system includes filtering a first wideband RF signal using a wideband filter bank. Filtering the first RF signal includes separating the first wideband RF signal into frequency cluster signals, where each frequency cluster signal of the frequency cluster signals includes different frequency ranges, the first wideband RF signal includes multiple RF bands, and each of the different frequency ranges comprises a plurality of RF bands of the multiple RF bands. The method further includes band stop filtering at least one of the frequency cluster signals to produce a band stopped frequency cluster signal.

A radio frequency identification (RFID) tag includes an antenna structure operable to receive a radio frequency (RF) signal, an RF signal circuit operable to, when enabled, produce the RF signal, a sensing element operably coupled to the antenna structure, a memory, and a processing module. When in a calibration mode, the processing module adjusts the input impedance until a measured power level is substantially equal to the desired input power level, and generates a first digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and stores the first digital value in the memory, where the first digital value is representative of a known condition. In a sense mode, the processing module adjusts the input impedance until a second measured power level is substantially equal to the desired input power level, and generates a second digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and the desired power level, and stores the second digital value in the memory, where the second digital value is representative of an unknown condition.

A radio frequency identification (RFID) tag includes an antenna structure operable to receive a radio frequency (RF) signal, an RF signal circuit operable to, when enabled, produce the RF signal, a sensing element operably coupled to the antenna structure, a memory, and a processing module. When in a calibration mode, the processing module adjusts the input impedance until a measured power level is substantially equal to the desired input power level, and generates a first digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and stores the first digital value in the memory, where the first digital value is representative of a known condition. In a sense mode, the processing module adjusts the input impedance until a second measured power level is substantially equal to the desired input power level, and generates a second digital value based on the amount of the adjustment a power difference between a measured first input power level and a desired power level, and the desired power level, and stores the second digital value in the memory, where the second digital value is representative of an unknown condition.

A notch filter includes a first inductor coupled between an input node and an output node, a dual-resonator structure coupled between the input node and the output node, and a second inductor coupled between the dual-resonator structure and ground, and a bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

A notch filter includes a first inductor coupled between an input node and an output node, a dual-resonator structure coupled between the input node and the output node, and a second inductor coupled between the dual-resonator structure and ground, and a bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.