A filtering device includes a low-pass filter (LPF), a noise estimation circuit and a first combining circuit. The LPF receives and filters a pre-filtering signal to generate an output signal of the filtering device. The noise estimation circuit estimates an estimated noise signal according to the output signal and the pre-filtering signal. The first combining circuit subtracts the estimated noise signal from an input signal of the filtering device to generate the pre-filtering signal.

A circuit comprises a Sallen-Key filter, which includes a source follower that implements a unity-gain amplifier; and a programmable-gain amplifier coupled to the Sallen-Key filter. The circuit enables programmable gain via adjustment to a current mirror copying ratio in the programmable-gain amplifier, which decouples the bandwidth of the circuit from its gain settings. The programmable-gain amplifier can comprise a differential voltage-to-current converter, a current mirror pair, and programmable output gain stages. The Sallen-Key filter and at least one branch in the programmable-gain amplifier can comprise transistors arranged in identical circuit configurations.

A circuit comprises a Sallen-Key filter, which includes a source follower that implements a unity-gain amplifier; and a programmable-gain amplifier coupled to the Sallen-Key filter. The circuit enables programmable gain via adjustment to a current mirror copying ratio in the programmable-gain amplifier, which decouples the bandwidth of the circuit from its gain settings. The programmable-gain amplifier can comprise a differential voltage-to-current converter, a current mirror pair, and programmable output gain stages. The Sallen-Key filter and at least one branch in the programmable-gain amplifier can comprise transistors arranged in identical circuit configurations.

A device comprises a differential voltage-mode filter circuit comprising first and second voltage-mode filter circuits, and a neutralization network. The first and second voltage-mode filter circuits each comprise a unity gain buffer having a nonzero output impedance. The neutralization network comprises a first neutralization impedance circuit which couples an input of the first voltage-mode filter circuit to an output of the second voltage-mode filter circuit, and a second neutralization impedance circuit which couples an input of the second voltage-mode filter circuit to an output of the first voltage-mode filter circuit. The neutralization network is configured to correct a frequency response of the first and second voltage-mode filter circuits by at least one of cancelling and compensating for at least one transmission zero of a transfer function of each of the first and second voltage-mode filter circuits, which results from the nonzero output impedance of the respective unity gain buffers.

In general the embodiments described herein can provide alternating-current (AC) resonating filters. These resonating filters comprise a transmission line, a first resonator, and a second resonator. The first resonator is configured to block AC signals in a first frequency range, while the second resonator is configured to block AC signals in a second frequency range, where the second frequency range is higher than the first frequency range. The transmission line has a first node coupled to an AC source, and the first resonator is coupled to the transmission line a first distance from the first node, and the second resonator is coupled to the transmission line a second distance from the first node, where the second distance is greater than the first distance. When so configured the resonating filter can effectively block signals in multiple selected frequency bandwidths.

Exemplary embodiments of the present disclosure are related to baseband filters. A device may include a digital-to-analog converter (DAC) configured to output a DC current. The device may also include an operational amplifier coupled to an output of the DAC and configured to bias an input stage of the operational amplifier with the DC current.

A circuit comprises a Sallen-Key filter, which includes a source follower that implements a unity-gain amplifier; and a programmable-gain amplifier coupled to the Sallen-Key filter. The circuit enables programmable gain via adjustment to a current mirror copying ratio in the programmable-gain amplifier, which decouples the bandwidth of the circuit from its gain settings. The programmable-gain amplifier can comprise a differential voltage-to-current converter, a current mirror pair, and programmable output gain stages. The Sallen-Key filter and at least one branch in the programmable-gain amplifier can comprise transistors arranged in identical circuit configurations.

Exemplary embodiments of the present disclosure are related to baseband filters. A device may include a digital-to-analog converter (DAC) configured to output a DC current. The device may also include an operational amplifier coupled to an output of the DAC and configured to bias an input stage of the operational amplifier with the DC current.

Filter circuits with emitter follower transistors and servo loops, and associated methods and apparatuses, are disclosed herein. In some embodiments, a filter circuit may include: a resistor-capacitor network having an input to receive an input signal; an emitter follower transistor, coupled to the resistor-capacitor network, wherein the filter circuit has an output to provide an output signal from the emitter of the emitter follower transistor; a current source to provide a constant reference current; and a current-buffering servo loop circuit, coupled to the emitter follower transistor and the current source, including a current buffer and a controlled current sink to maintain the collector current and the emitter current of the emitter follower transistor equal to the constant reference current.

Active-RC low-pass filters based on R-0.5R ladders are implemented to provide high linear and low power design solutions for integrated biomedical applications. Among various R-R ladders family, R-0.5R ladders provide the best low frequency selectivity characteristics. The filters exhibit ultra-low pole frequencies and occupy relatively compact silicon areas by using the R-0.5R ladders.