Embodiments of the disclosure relate to a frequency selective low noise amplifier (LNA) circuit, which includes a transconductive LNA(s). In one aspect, filter circuitry is provided in a degeneration path of a transconductive LNA(s) to pass in-band frequencies and reject out-of-band frequencies by generating low impedance and high impedance at the in-band frequencies and the out-of-band frequencies, respectively. However, having the filter circuitry in the degeneration path may cause instability in the transconductive LNA. As such, a feedback path is coupled between an input node of the transconductive LNA(s) and the degeneration path to provide a feedback to improve stability of the transconductive LNA(s). In addition, the feedback can help improve impedance match in the frequency selective LNA circuit. As a result, the transconductive LNA(s) is able to achieve improved noise figure (NF) (e.g., below 1.5 dB), return loss, linearity, and stability, without compromising LNA gain.

In a folded cascode operational amplifier circuit, a source is connected to a back gate in each of third and fourth transistors that are cascode-connected to first and second transistors, which are an electric current source that returns an electric current signal output by a differential pair of an input stage. In the third and fourth transistors, an active parasitic element exists due to its device structure. When a falling edge signal of a rectangular wave is input, and electric current is supplied to the source of the third transistor to increase its electric potential, electric current flows into the drain from the back gate via the active parasitic element in an on state, in order to rapidly charge a capacitor. Thereby, a fifth transistor turns on within a shorter time, in order to improve an internal slew rate.

An apparatus includes an amplifier. The amplifier has two inputs, and an output. The amplifier has a pole in its transfer function. The frequency of the pole depends on the output current of the amplifier. The amplifier further includes a pole frequency tracking (PFT) circuit. The PFT circuit includes a source follower circuit.

Disclosed are an apparatus and method of processing an audio signal to optimize audio for a room environment. One example method of operation may include recording the audio signal generated within a particular room environment and processing the audio signal to create an original frequency response based on the audio signal. The method may also include identifying a target sub-region of the frequency response which has a predetermined area percentage of a total area under a curve generated by the frequency response, determining whether the target sub-region is a narrow energy region, creating a filter to adjust the frequency response, and applying the filter to the audio signal.

Disclosed are an apparatus and method of processing an audio signal to optimize audio for a room environment. One example method of operation may include recording the audio signal generated within a particular room environment and processing the audio signal to create an original frequency response based on the audio signal. The method may also include identifying a target sub-region of the frequency response which has a predetermined area percentage of a total area under a curve generated by the frequency response, determining whether the target sub-region is a narrow energy region, creating a filter to adjust the frequency response, and applying the filter to the audio signal.

A circuit includes a differential input stage amplifier that receives a differential input voltage and generates an output voltage based on a difference in the differential input voltage. A feedback loop provides feedback from an output of the differential input stage amplifier to input tail current of the differential input stage amplifier. The feedback loop enables class AB operation of the differential input stage amplifier. At least one gain reducer is operatively coupled to the feedback loop to reduce the gain of the feedback loop. The gain reducer has a resistance value that varies inversely proportional to loop current in the feedback loop to reduce the gain of the feedback loop as loop current increases.

One example includes a hot-swap control system. The system includes a sense resistor network provides a sense voltage in response to an output current. The system also includes a sense control circuit includes a chopper amplifier system arranged in a servo feedback arrangement to generate a monitoring voltage having an amplitude that is associated with the output current based on the sense voltage. A notch filter chopping stage filters out signal ripple in the chopper amplifier system across a unity-gain bandwidth of the chopper amplifier system, and a capacitive compensation network provides stability-compensation of the chopper amplifier system across the unity-gain bandwidth. A transconductance amplifier configured to compare the monitoring voltage with a predetermined reference voltage to generate a control voltage. The system further includes a power transistor configured to conduct the output current to an output based on the control voltage.

In general, this disclosure is directed to a mixer amplifier that can be utilized within a chopper stabilized instrumentation amplifier. The chopper stabilized instrumentation amplifier may be used for physiological signal sensing, impedance sensing, telemetry or other test and measurement applications. In some examples, the mixer amplifier may include a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.

An audio amplifier, including: at least a two stage amplifier configured to receive an input signal and output an amplified output signal, the at least a two stage amplifier including at least one stage amplifier and an output stage amplifier; and an auxiliary stage amplifier having an input coupled to an output of the at least one stage amplifier and an input of the output stage amplifier.

A circuit includes a differential input stage amplifier that receives a differential input voltage and generates an output voltage based on a difference in the differential input voltage. A feedback loop provides feedback from an output of the differential input stage amplifier to input tail current of the differential input stage amplifier. The feedback loop enables class AB operation of the differential input stage amplifier. At least one gain reducer is operatively coupled to the feedback loop to reduce the gain of the feedback loop. The gain reducer has a resistance value that varies inversely proportional to loop current in the feedback loop to reduce the gain of the feedback loop as loop current increases.