Methods and systems for a configurable low-noise amplifier with programmable band-selection filters may comprise a receiver with a low-noise amplifier (LNA) with first and second input terminals and differential output terminals; a low pass filter operably coupled to the LNA; a high pass filter operably coupled to the second input terminal of the LNA; and a signal source input coupled to the low pass filter and the high pass filter. The LNA may be operable to receive signals in a pass band of the high pass filter and a pass band of the low pass filter. The receiver may be operable to amplify input signals in the pass band of a first filter but not signals in the pass band of the second filter by operably coupling the second to ground.

A bandpass filter that provides a wide gain control range is provided. The bandpass filter performs channel filtering and gain control while maintaining the bandpass characteristic of the bandpass filter. The bandpass filter enables gain control for a wide signal amplitude range while maintaining performance characteristics, such as an out-of-band attenuation ratio capable of high linearity and good pass-band flatness.

A bandpass filter that provides a wide gain control range is provided. The bandpass filter performs channel filtering and gain control while maintaining the bandpass characteristic of the bandpass filter. The bandpass filter enables gain control for a wide signal amplitude range while maintaining performance characteristics, such as an out-of-band attenuation ratio capable of high linearity and good pass-band flatness.

A variable gain amplifier having stabilized frequency response for widened gain control range. A resistor-capacitor compensation network is provided between two differential current input ports and corresponding emitter nodes of cross-coupled four transistors in the variable gain amplifier to desensitize the gain control voltages to the system noise and provide compensation to the VGA frequency response when the differential gain control voltage varies the gain setting, yielding a substantially stabilized frequency response over a 3 dB bandwidth ranging from 1 GHz to 60 GHz with a widened gain control range up to 12 dB without increasing power consumption.

A communication system includes a carrier generator configured to generate a first carrier signal and a demodulator configured to demodulate a modulated signal responsive to the first carrier signal. The demodulator includes a filter and a gain adjusting circuit. The filter is configured to filter a first signal. The first signal is a product of the first carrier signal and the modulated signal. The filter has a first cutoff frequency and a gain. The gain of the filter is controlled by a set of control signals. The gain adjusting circuit is configured to adjust the gain of the filter based on a voltage of the filtered first signal or a voltage of a second signal. The adjustable gain circuit is configured to generate the set of control signals.

A voltage gain amplifier (VGA) configured to have reduced supply noise. The VGA includes first resistor, first FET, and a first current-source coupled between first and second voltage rails. The VGA includes second resistor, second FET, and second current-source coupled between the voltage rails. A variable resistor is coupled between the respective sources of the first and second FETs. Variable capacitors are coupled between the first or a third voltage rail and the sources of the first and second input FETs, respectively. If capacitors are coupled to the first voltage rail, noise cancellation occurs across the gate-to-source voltages of the FETs if an input differential signal applied to the gates of the FETs is derived from a supply voltage at the first voltage rail. If capacitors are coupled to the third rail, supply noise is reduced if the supply voltage at the third rail is generated by a cleaner regulator.

A circuit includes an electrical gain element, a variable reactance element, and a controller. The electrical gain element is arranged to receive and change an amplitude of a signal over a set frequency range. The variable reactance element is connected to the electrical gain element. The controller is configured to control the variable reactance element to have a reactance such that the electrical gain element has a set gain slope as a function of signal frequency over the set frequency range.

An optical communication system, a linear optical receiver, and an Integrated Circuit (IC) chip are disclosed, among other things. One example of the disclosed IC chip includes a transimpedance amplifier that receives an input electrical signal from a photodiode and provides an amplified version of the input electrical signal as an output, at least one variable gain amplifier that receives the amplified electrical signal output by the transimpedance amplifier and a bandwidth control mechanism that extends a bandwidth of the second amplified output at a maximum gain of the second amplification phase and also reduces a peaking of the second amplified output at a minimum gain of the second amplification phase.

A compensation circuit includes an amplifier coupled between a first voltage terminal and a common terminal. The amplifier has a first output terminal. A current source transistor has a current path coupled between a second voltage terminal and a second output terminal. A threshold voltage sense transistor has a current path coupled between the first and second output terminals. A gate and drain of the threshold voltage sense transistor are connected. An output transistor having a current path coupled between the first output terminal and a third output terminal has a gate coupled to the second output terminal.

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.