According to at least one aspect, a filter network is provided. The filter network comprises: an active filter comprising an amplifier (e.g., an operational amplifier), wherein the active filter is configured to add at least one member selected from the group consisting of a pole and a zero to a transfer function of the filter network; a passive filter coupled to the active filter and configured to add at least one pole to the transfer function of the filter network; and a non-inverting amplifier (e.g., a voltage buffer) having an input coupled to the passive filter and an output coupled to the active filter.

A sensor apparatus includes a resonator, a transducer, a damping resistor, a first switch, a filter stage, a second switch, and a noise rejection stage. The transducer is configured to detect a position of the resonator. The damping resistor is configured to electrostatically actuate the transducer and convert a thermomechanical noise of the resonator to an electromechanical noise. The first switch is configured to receive a first signal from the transducer. The filter stage is configured to receive the first signal and adjust a phase and a gain of the first signal and output a filtered first signal. The second switch is configured to receive a second signal from the transducer. The noise rejection stage is configured to receive the filtered first signal and the second signal and reduce the filtered first signal from an output signal.

A circuit having an input and an output, the circuit comprising: a first amplifier having a first input, a second input and an output coupled to the output of the circuit; a first capacitor having a first terminal coupled to the first input of the first amplifier and a second terminal coupled to the output of the first amplifier; a first resistor having a first terminal coupled to the first input of the first amplifier and a second terminal; a buffer having an output coupled to the second terminal of the first resistor and an input; a second resistor having a first terminal coupled to the output of the first amplifier and a second terminal coupled to the input of the buffer; a second capacitor coupled between the input of the buffer and ground; and a third resistor coupled between the input of the buffer and the input of the circuit.

A calibration device includes a signal generator and a processor. The signal generator is configured to provide an input signal to a filter circuit, wherein the filter circuit has a real time constant and is configured to receive the input signal to output an output signal. The processor is configured to calculate a real gain according to the output signal and the input signal, compare the real gain with a target gain to obtain a comparison result and determine whether to adjust the real time constant of the filter circuit according to the comparison result. The present disclosure also provides a calibration method.

An integrated circuit that includes an analog frequency-selective gain filter having a frequency-selective gain corresponding to a high-pass filter prior to an analog-to-digital converter (ADC) is described. During operation, the analog frequency-selective gain filter may provide frequency-selective gain (such as a high-pass filter characteristic) to an electrical signal corresponding to a received signal (such as a LiDAR signal, a sonar signal, an ultrasound signal and/or a radar signal) in a ranging receiver. Note that the received signal may correspond to a received frequency-modulated continuous-wave (FMCW) signal. Moreover, the integrated circuit may include a digital processing circuit after the ADC and control logic that instructs the digital processing circuit to characterize the frequency-selective gain (such as an amplitude and/or a phase at a frequency) during a calibration mode. Furthermore, the digital processing circuit may correct an output signal from the ADC based at least in part on the characterized frequency-selective gain.

In general, one aspect disclosed features an active choke circuit, comprising: a first three-winding choke; a second three-winding choke; and an amplifier; wherein a first winding of the first three-winding choke is electrically coupled in series with a first winding of the second three-winding choke; wherein a second winding of the first three-winding choke is electrically coupled in series with a second winding of the second three-winding choke; wherein a third winding of the first three-winding choke is electrically coupled to an input of the amplifier; and wherein a third winding of the second three-winding choke is electrically coupled to an output of the amplifier.

An RF signal is processed by coupling an input signal into a signal loop, the signal loop comprising a resonator and a processing block, and filtering the input signal in the signal loop to produce an output signal by obtaining a plurality of resonator outputs from the resonator and processing the plurality of resonator outputs to generate feedback signals. The feedback signals are connected to a point upstream of the resonator. At least one of the plurality of resonator outputs is processed in the processing block. The signal loop is definable by a transfer function having poles, and the plurality of resonator outputs are processed such that the poles of the transfer function are independently controllable.

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.

An active filter reduces Electro-Magnetic Interference (EMI) created by current flowing through a power line. The active filter connects to the power line at a single node through a connection capacitor. A sense current flows through the connection capacitor when the power line current changes. This sense current is applied to a non-inverting input of an op amp to drive a power amplifier circuit through a filter capacitor. The power amplifier circuit increases the current drive of the op amp to charge a transfer capacitor that converts the power amplifier output current to a transfer voltage. The transfer capacitor is connected to the connection capacitor so that the transfer voltage is injected back into the power line through the connection capacitor as an injected voltage that compensates for the sensed current. Op amp gain is adjustable by variable resistors that connect to the inverting input of the op amp.

A system includes a conductive chassis having a first ground terminal. The conductive chassis couples to a switching circuit having a second ground terminal and having a first switching frequency. The second ground terminal is electrically isolated from the first ground terminal. An active electromagnetic interference (EMI) filter has an output and first and second inputs, and is configured to receive a first AC voltage having a second switching frequency at the first input, receive a second AC voltage having the second switching frequency at the second input referenced to the first ground terminal, sense noise having the first switching frequency on at least one of the first or second inputs, and generate an injection signal at the output based on the detected noise. The output couples to at least one of the first or second inputs.