A digital amplifier that minimizes and restricts an analog signal system and uses a feedback signal and a dither signal is achieved. A pulse width modulator that adjusts a pulse width of a digital signal, a switching circuit that amplifies an output signal from the pulse width modulator, and a feedback signal generation unit that generates a feedback signal based on an output signal from the switching circuit are included, the pulse width modulator adjusts the pulse width of the digital signal with reference to the feedback signal, and the feedback signal generation unit includes a first amplifier that outputs a first amplified signal in which a difference between the output signal from the switching circuit and one of a reference voltage and a dither signal is amplified and a second amplifier that amplifies a difference between the first amplified signal and the other of the dither signal and the reference voltage and outputs the amplified difference as the feedback signal.

A filter includes multiple filter circuits. The filter circuits are coupled in series between an input terminal and an output terminal, to generate an output signal according to an input signal. One of the filter circuits operates as an active filter circuit or a passive filter circuit according to amplitude of the input signal.

Techniques for mitigating noise in a touch signal are disclosed. To reduce or eliminate noise in a touch signal, the touch activity can be filtered out of a touch signal, thus isolating the noise. In some examples, the noise is then provided to the non-inverting input port of a differential amplifier while the unfiltered touch signal is provided to the inverting input port of the differential amplifier. The noise, which is now common on both inputs, is automatically eliminated or reduced by the differential amplifier.

A variable filter for an RF circuit has a signal loop comprising a signal input port and a signal output port, and a plurality of circuit elements connected within the signal loop. The plurality of circuit elements comprise a multi-pole resonator comprising a plurality of frequency tunable resonators and an adjustable scaling block that applies a gain factor. Adjacent frequency tunable resonators within the multi-pole resonator are reciprocally coupled. A controller is connected to tune the multi-pole resonator and to adjust the gain factor of the adjustable scaling block such that the signal loop generates a desired bandpass response.

A filter can perform two filtering processes. The filter includes a switching circuit, a first filter circuit, and a second filter circuit. The first filter circuit is coupled to the switching circuit. The second filter circuit is coupled to the switching circuit. The first filter circuit performs a first filtering process on an input signal according to a state of the switching circuit. The first filter circuit and the second filter circuit work together to perform a second filtering process on the input signal according to the state of the switching circuit.

A filter includes a switching circuit, a first filter circuit, and a second filter circuit. The first filter circuit is coupled to the switching circuit. The second filter circuit is coupled to the switching circuit. The switching circuit is controlled to control the first filter circuit to perform a first filtering process on an input signal or control the first filter circuit to work in coordination with the second filter circuit to perform a second filtering process on the input signal.

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.

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.

An active filter comprising an operational amplifier, and a controller configured to control the bandwidth of the operational amplifier based on a filter cutoff frequency setting and/or a noise performance setting.

An active electromagnetic interference filter comprising an adjustable shunt impedance circuit, the adjustable shunt impedance circuit comprising a noise sensing branch that senses input noise and provides a noise voltage representative of the sensed noise, and an operational amplifier stage configured to generate, at an injection branch, an injection current based on the noise voltage.