An aspect includes a filtering method including operating a first filter to filter a first input signal to generate a first output signal; operating a second filter to filter a second input signal to generate a second output signal; and selectively coupling at least a portion of the second filter with the first filter to filter a third input signal to generate a third output signal. Another aspect includes a filtering method including operating switching devices to configure a filter with a first set of pole(s); filtering a first input signal to generate a first output signal with the filter configured with the first set of pole(s); operating the switching devices to configure the filter with a second set of poles; and filtering a second input signal to generate a second output signal with the filter configured with the second set of poles.

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.

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.

Systems and methods for analog finite impulse response (FIR) filters are provided. In certain embodiments, a receiver includes a cascade of a mixer, an analog FIR filter, and an analog-to-digital converter (ADC). By including the analog FIR filter along the signal path between the mixer and the ADC, design constraints of the ADC are relaxed. For example, the ADC can operate with relaxed specifications with respect to resolution and/or dynamic range when the analog FIR filter is included. The analog FIR filter can include a controllable transconductance circuit that delivers an integration current to a capacitor over an integration period, with the analog FIR filter's coefficients used to change the transconductance setting of the controllable transconductance circuit to different values over the integration period.

Systems and methods for analog finite impulse response (FIR) filters are provided. In certain embodiments, a receiver includes a cascade of a mixer, an analog FIR filter, and an analog-to-digital converter (ADC). By including the analog FIR filter along the signal path between the mixer and the ADC, design constraints of the ADC are relaxed. For example, the ADC can operate with relaxed specifications with respect to resolution and/or dynamic range when the analog FIR filter is included. The analog FIR filter can include a controllable transconductance circuit that delivers an integration current to a capacitor over an integration period, with the analog FIR filter's coefficients used to change the transconductance setting of the controllable transconductance circuit to different values over the integration period.

A method and apparatus for modifying or controlling a resonator connected to a signal loop having an input (18828), an output (18822), and a closed loop frequency response. The signal loop has a primary resonator (18810) having a primary frequency response. There is at least one adjustable resonator (18812) having an adjustable frequency (f) and a secondary Q-factor. An adjustable scaling block (18824) applies a gain factor (g). A controller is connected to the at least one adjustable resonator (18812) and the adjustable scaling block (18824). The controller has instructions to adjust the closed loop frequency response toward a desired closed loop frequency response by controlling the adjustable frequency (f) of the at least one adjustable resonator (18812) and the gain factor (g) of the adjustable scaling block (18824).

A radio-frequency filter includes a series-arm circuit on a circuit path that connects a first input/output terminal and a second input/output terminal. A parallel-arm circuit is connected to a node on the path and ground. The series-arm circuit includes a first impedance element, a first switch element connected to the first impedance element, and a series-arm resonator connected in parallel to the first impedance element and the first switch element. The parallel-arm circuit includes a first parallel-arm resonator, and a first switch circuit connected in series to the first parallel-arm resonator, the first switch circuit includes a second switch element. The first and second switch elements and the second switch elements include one or more transistors, and a gate width of the transistors included in the second switch element is larger than that of at least one of the transistors included in the first switch element.

A multiple-gain transconductance amplifier circuit is presented. It is developed by utilizing programmable gain source-coupling differential pair output stage forming multiple-gain transconductance amplifier outputs. A reconfigurable n.sup.th-order filter based on a multi-gain transconductance amplifier where the multi-gain transconductance amplifier includes a linear voltage-to-current converter and a programmable current-folding output stage was implemented. The filter achieves independent programmability while still using a single active device per pole. Further, the proposed multiple-gain transconductance amplifier can be employed to design poly phase filters and transconductance amplifier cell for an amplifier-based low-dropout regulator.

An aspect includes a filtering method including operating a first filter to filter a first input signal to generate a first output signal; operating a second filter to filter a second input signal to generate a second output signal; and selectively coupling at least a portion of the second filter with the first filter to filter a third input signal to generate a third output signal. Another aspect includes a filtering method including operating switching devices to configure a filter with a first set of pole(s); filtering a first input signal to generate a first output signal with the filter configured with the first set of pole(s); operating the switching devices to configure the filter with a second set of poles; and filtering a second input signal to generate a second output signal with the filter configured with the second set of poles.

An example circuit includes: an inverter-based filter; a voltage regulator having an input and an output, the output of the voltage regulator providing a supply voltage to bias the inverter-based filter; a ring oscillator having a supply input and an output, the supply input of the ring oscillator coupled to the output of the voltage regulator; a control circuit coupled to the output of the ring oscillator and the input of the voltage regulator, the control circuit configured detect an oscillation frequency of the ring oscillator and to adjust the voltage regulator in response to the oscillator frequency.