A filter circuit comprising: a signal path for carrying a signal from an input to an output; the signal path comprising a first reactive component; a first node on the signal path; a first series resonant circuit comprising at least a second reactive component in series with a third reactive component, the first series resonant circuit being connected between the first node and a ground; an active circuit; the active circuit comprising a voltage controlled current source (VCCS) arranged to change the current flow through the second reactive component in dependence on a voltage sensed (or measured) on the signal path. The first series resonant circuit forms a single harmonic trap with a notch frequency defined by the component values of its reactive components. The effectiveness of the series resonant circuit is dependent upon the strength with which it draws current from the signal path at its resonant frequency.

In accordance with an embodiment, a method of operating a piezoelectric transducer configured to transduce mechanical vibrations into transduced electrical signals at a pair of sensor electrodes includes stimulating a resonant oscillation of the piezoelectric transducer by applying at least one pulse electrical stimulation signal to the pair of sensor electrodes; detecting, at the pair of sensor electrodes, at least one electrical signal resulting from the stimulated resonant oscillation, wherein the at least one electrical signal resulting from the stimulated resonant oscillation oscillates at a resonance frequency of the piezoelectric transducer; measuring a frequency of oscillation of the at least one electrical signal resulting from the stimulated resonant oscillation to obtain a measured resonance frequency of the piezoelectric transducer; and tuning a stopband frequency of a notch filter coupled to the piezoelectric transducer to match the measured resonance frequency of the piezoelectric transducer.

The embodiments of the present disclosure provide a signal processing circuit and a signal processing method. The signal processing circuit may include a control circuit, a switch circuit, an analog circuit, and at least two signal acquisition circuits. The at least two signal acquisition circuits may be configured to acquire at least two-channel target signals. The switch circuit may be configured to control conduction between the at least two signal acquisition circuits and the analog circuit, so that the target signal acquired by a part of the at least two signal acquisition circuits may be transmitted to the analog circuit at the same time. The analog circuit may be configured to process the received target signal. The control circuit may be configured to receive the processed target signal and sample the processed target signal.

One or more systems, devices and/or methods of use provided herein relate to a device that can facilitate selective switching between band pass and band stop filter modes and/or can provide reflectionless or near reflectionless function. A device can comprise a filter circuit coupled between a pair of ports and comprising a direct current superconducting quantum interference device (DC SQUID), wherein the filter circuit is selectively activatable by varying the inductance of the DC SQUID. Applying flux bias to the DC SQUID can allow for the switching between the band pass and band stop filter modes.

A notch filter is coupled to a first input node and a second input node, and is configured to present a capacitive load to a differential signal provided to the first and second input nodes, and to present a series-resonant inductive-capacitive load to a common-mode signal provided to the first and second input nodes. The notch filter includes a transformer and a capacitor bank. The transformer includes a first winding having a positive-polarity terminal coupled to the first input node and a second winding having a positive-polarity terminal coupled to the second input node. The capacitor bank includes a first capacitor coupled between a negative-polarity terminal of the first winding and a bias node, and a second capacitor coupled between a negative-polarity terminal of the second winding and the bias node. The first and second capacitors may be variable capacitors.

A method includes receiving a radio frequency (RF) input signal using at least one non-reciprocal circulator. The method also includes generating an RF output signal using at least one of multiple reflective filter elements. Each reflective filter element is configured to receive an RF signal from the at least one non-reciprocal circulator and to provide a filtered RF signal to the at least one non-reciprocal circulator. The reflective filter elements include amplitude change reflectors configured to modify amplitudes of the RF signal at different frequencies. The RF output signal represents the RF input signal as modified by the at least one of the reflective filter elements.

A method includes receiving a radio frequency (RF) input signal using at least one non-reciprocal circulator. The method also includes generating an RF output signal using at least one of one or more reflective circuit elements. Each reflective circuit element is configured to receive an RF signal from the at least one non-reciprocal circulator and to provide a modified RF signal to the at least one non-reciprocal circulator. The RF output signal represents the RF input signal as modified by the at least one of the one or more reflective circuit elements.

A filter for motor speed measurement signals includes one or more resonators configured to filter signals having a frequency that is proportional by a predetermined factor to the frequency of the motor whose speed is measured.

An on-chip balun comprising a primary side, a secondary side, and an integrated notch filter.

Techniques are disclosed for filtering a radio frequency (RF) signal using an N-path bandstop filter with an extended, spurious-free upper passband. In an embodiment, a bandstop filter includes a bank of three switched capacitors in series with the RF signal path through the filter, in contrast to 4- or 8-capacitor banks or other bandstop filters where N is a power of 2. In this 3-path example configuration, an undesirable spurious bandstop notch at the 3.sup.rd and 5.sup.th harmonics of the clock frequency are eliminated or substantially reduced, improving performance of the filter in the desired passbands while preserving the notch in the desired stopband at high RF signal frequencies. Another N-path bandstop filter embodiment includes a bridged T-coil circuit, which absorbs a shunt capacitance of the bandstop filter into the bridged T-coil circuit.