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.

According to one embodiment, a low noise amplifier (LNA) circuit includes a first stage which includes: a first transistor; a second transistor coupled to the first transistor; a first inductor coupled in between an input port and a gate of the first transistor; and a second inductor coupled to a source of the first transistor, where the first inductor and the second inductor resonates with a gate capacitance of the first transistor for a dual-resonance. The LNA circuit includes a second stage including a third transistor; a fourth transistor coupled between the third transistor and an output port; and a passive network coupled to a gate of the third transistor. The LNA circuit includes a capacitor coupled in between the first and the second stages, where the capacitor transforms an impedance of the passive network to an optimal load for the first amplifier stage.

Various embodiments of the invention relate to a tunable gain equalizer to enable a RF output with constant gain over a wide frequency band. The tunable gain equalizer comprises a series path formed by a plurality of adjustable capacitors coupled in series, and two shunt paths coupled to the series path. The adjustable capacitors may be varactors coupled to a biasing voltage for capacitance adjustment. The shunt paths comprise inductors to enable a positive gain slope to compensate negative gain slope of RF amplifiers. The shunt paths may be bridged by one or more branches connected between the two shunt paths. The bridged branches provide a higher tunable gain slope amount and a better input/output matching. By making the biasing voltage of the tunable gain equalizer temperature dependent, the tunable gain equalizer is able to generate a temperature dependent gain slope to offset the temperature variation influence.

A communication system includes a modulator configured to generate a modulated signal responsive to at least a data signal, and a demodulator configured to demodulate the modulated signal responsive to a first carrier signal. The demodulator includes a filter configured to generate a filtered first signal based on a first signal, and a gain adjusting circuit coupled to the filter. The first signal is based on the first carrier signal and modulated signal. The filter has a gain controlled by a set of control signals. The gain adjusting circuit is configured to adjust the gain of the filter, and to generate the set of control signals based on a voltage of the filtered first signal and a voltage of the first signal. The gain adjusting circuit includes a first peak detector coupled to the filter, and configured to detect a peak value of the voltage of the filtered first signal.

A communication system includes a modulator configured to generate a modulated signal responsive to at least a data signal, and a demodulator configured to demodulate the modulated signal responsive to a first carrier signal. The demodulator includes a filter configured to generate a filtered first signal based on a first signal, and a gain adjusting circuit coupled to the filter. The first signal is based on the first carrier signal and modulated signal. The filter has a gain controlled by a set of control signals. The gain adjusting circuit is configured to adjust the gain of the filter, and to generate the set of control signals based on a voltage of the filtered first signal and a voltage of the first signal. The gain adjusting circuit includes a first peak detector coupled to the filter, and configured to detect a peak value of the voltage of the filtered first signal.

A receiving circuit and method for increasing bandwidth are provided. The receiving circuit includes a linear equalizer circuit and a variable gain amplifier. The linear equalizer circuit includes a first negative impedance converter, to generate a first capacitance. The variable gain amplifier is coupled to the linear equalizer circuit. The variable gain amplifier includes a first-stage gain circuit and a feedback circuit. The first-stage gain circuit is coupled to the feedback circuit, and the feedback circuit generates a zero-point at the output end of the first-stage gain circuit.

A low noise amplifier includes at least two variable gain amplifier stages, each variable gain amplifier configured to accept an input signal and to provide a load driving signal; a tunable bandpass filter connected as a load to each variable gain amplifier stage, wherein each bandpass filter includes a resonant tank, each resonant tank including an inductor, wherein each inductor of each resonant tank is oriented in orthogonal relation with respect to each respective longitudinal axis of each next inductor, the orthogonal relation of the respective longitudinal axes configured to reduce mutual coupling between the tunable bandpass filters; a cross-coupled transistor pair, and at least one cross-coupled compensation transistor pair biased in a subthreshold region configured to add a transconductance component as a function of a load driving signal; and, a controller circuit configured to tune each tunable bandpass filter.

A low noise amplifier includes at least two variable gain amplifier stages, each variable gain amplifier configured to accept an input signal and to provide a load driving signal; a tunable bandpass filter connected as a load to each variable gain amplifier stage, wherein each bandpass filter includes a resonant tank, each resonant tank including an inductor, wherein each inductor of each resonant tank is oriented in orthogonal relation with respect to each respective longitudinal axis of each next inductor, the orthogonal relation of the respective longitudinal axes configured to reduce mutual coupling between the tunable bandpass filters; a cross-coupled transistor pair, and at least one cross-coupled compensation transistor pair biased in a subthreshold region configured to add a transconductance component as a function of a load driving signal; and, a controller circuit configured to tune each tunable bandpass filter.

Embodiments provide an audio amplifier circuit with integrated (built-in) filter (e.g., a digital-to-analog converter (DAC) filter). The audio amplifier circuit may have a non-flat (e.g., low-pass) closed loop frequency response. The audio amplifier circuit may include a low pass filter coupled between an input terminal that receives the input analog audio signal and the input of the gain stage of the amplifier. In some embodiments, additional impedance networks may be included to produce a desired low-pass filter response, such as a second order filter, a third order filter, and/or another suitable filter response. Other embodiments may be described and/or claimed.