A reconfigurable analog filter includes a transimpedance amplifier configured to convert a current signal into a voltage signal, an input capacitor configured to form a current-mode low pass filter together with an input impedance of the transimpedance amplifier, a variable load circuit including at least one switch configured to selectively close a circuit path to provide a resistor and/or a capacitor as a load of the transimpedance amplifier according to a control signal, and a low pass filter configured to filter the voltage signal.

A circuit includes a filter, a first inverter, and a second inverter. The filter is coupled to an input of the first inverter. The second inverter includes an input and an output. The input of the second inverter is coupled to the output of the first inverter. The output of the second inverter is coupled to the input of the first inverter.

A hybrid filter circuit for reducing common-mode interference signals with frequencies of at least 150 kHz in a power line with at least one phase. The circuit has a passive filter stage and an active filter unit with an active filter stage. The circuit can be coupled to an electrical device on a load side and to a power supply system on a supply side via the power line. The first active filter stage includes a sensor for measuring a common mode noise signal in the power line and a feedback unit with an active amplifier unit for generating a compensation signal counteracting the common mode noise signal, which is coupled into the power line via an output of the first active filter stage. The passive filter stage and the active filter circuit are arranged in cascade between the load terminal and a supply terminal.

A tunable filter is provided. The tunable filter includes: a filter input; a filter output; at least one feedback loop coupled between the filter output and the filter input, where the at least one feedback loop includes at least one tunable feedback capacitance which is configured to tune a cut-off frequency of the tunable filter; and an active element, coupled between the filter input and the filter output and configured to drive the at least one tunable feedback capacitance, the active element having a transfer function with a primary pole and at least one secondary pole, where the active element includes a first stabilization element that is coupled to a first internal node of the active element.

A compensation filter and a method for activating a compensation filter are disclosed. In an embodiment a compensation filter includes an operational amplifier, a capacitive element, a first and a second resistive element and a current converter. The compensation filter is configured to attenuate a common mode interference in a critical frequency range.

An error amplifier for a pulse width modulation circuit is described. The amplifier includes an operational amplifier configured as an integrator and a feedback loop coupled between a signal output of the operational amplifier and an inverting input of the operational amplifier. The feedback loop comprises a feedback capacitor coupled to the signal output, a feedback resistor coupled to the feedback capacitor, and an integrator resistor coupled to the feedback resistor and the inverting input of the operational amplifier. A junction between the feedback resistor and the integrator resistor is configured to receive an input signal and a junction between the feedback capacitor and the feedback resistor is configured to receive a feedback signal from the pulse width modulation circuit.

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 coupling module can be used to communicate high speed signals between an optical transceiver and a processing module of an optical communication device, such as an optical line termination (OLT) or an optical network unit (ONU). The coupling module can adjust the common mode voltage level of a differential signal output by the optical transceiver to the common mode voltage level required by the processing module. In addition, the coupling module splits each of the differential output signals from the optical transceiver and passes the split signals to both a high-pass filter and a low-pass filter that are connected in parallel. The outputs of the high-pass filter and the low-pass filter from different paths of the differential signal are cross-coupled and combined to provide a differential signal to the processing module.

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.

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.