The invention is a filter circuit for noise cancelling earphones wherein one end of the filter circuit for noise cancelling earphones is connected to the circuit for noise cancelling microphones. In the circuit starting from one end of the said noise cancelling microphones circuit connected to the resistor R0 set the first current node. The other end of the said noise cancelling microphones circuit is connected to the ground while the other end of the said resistor R0 is connected to the high level. Lead a circuit from the first current node connected to the input end of high pass circuit, the output end of the said high pass circuit is connected to the input end of gain amplifier circuit, the output end of the said gain amplifier circuit is connected to the input end of trap circuit, the output end of the said trap circuit is connected to the input end of gain feedback amplifier circuit through the resistor R7, the output end of the said gain feedback amplifier circuit is connected to the positive electrode of the speaker circuit while the negative electrode is connected to the ground.

In some examples, a circuit includes an amplifier, a resistor, and a damping network. The amplifier has an amplifier output and first and second amplifier inputs. The first amplifier input is adapted to be coupled to a first terminal, and the second amplifier input is configured to receive a reference voltage. The resistor is coupled between the amplifier output and the first amplifier input. The damping network is coupled between the amplifier output and the first terminal.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.

According to one embodiment, in a complex band pass filter, a second input signal to be supplied to a second active filter circuit has a substantially 90 degree phase difference from a first input signal to be supplied to a first active filter circuit. The first feedback circuit includes a first element having a first impedance and feeds back an output signal of the first active filter circuit to input side of the second active filter circuit. The second feedback circuit includes a second element having a second impedance different from the first impedance and feeds back an output signal of the second active filter circuit to input side of the first active filter circuit. The output circuit outputs an output signal according to a signal from the first active filter circuit and to a signal from the second active filter circuit.

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.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.

The floating immittance emulator is presented in four embodiments in which four new topologies for emulating floating immittance functions are detailed. Each circuit uses three current-feedback operational-amplifiers (CFOAs) and three passive elements. The present topologies can emulate lossless and lossy floating inductances; capacitance, resistance, and inductance multipliers; and frequency-dependent positive and negative resistances.