An active feedback low-noise amplifier includes a feedback transistor whose source couples through a feedback path to an input signal node. A bias transistor biases the source of the feedback transistor with a bias current responsive to an input signal carried on the input signal node.

A variable-current trans-impedance amplifier (TIA) for an ultrasound device is described. The TIA may be coupled to an ultrasonic transducer to amplify an output signal of the ultrasonic transducer representing an ultrasound signal received by the ultrasonic transducer. During acquisition of the ultrasound signal by the ultrasonic transducer, one or more current sources in the TIA may be varied. The variable-current trans-impedance amplifier may include multiple stages, including a first stage having N-P transistor pairs configured to receive an input signal and produce a single-ended amplified signal.

An active feedback low-noise amplifier includes a feedback transistor whose source couples through a feedback path to an input signal node. A bias transistor biases the source of the feedback transistor with a bias current responsive to an input signal carried on the input signal node.

A signal output circuit includes an inverting amplifier circuit, a feedback capacitor and a low pass filter. The inverting amplifier circuit includes an input terminal and an output terminal. The inverting amplifier circuit executes an inverting amplification based on an input signal to output a signal to the output terminal at a pull-up state. An output stage of the inverting amplifier circuit is an open collector or an open drain. The feedback capacitor is connected between the input terminal and the output terminal of the inverting amplifier circuit. The low pass filter has an input and an output. The input of the low pass filter is connected to the output terminal of the inverting amplifier. The output of the low pass filter is connected to the feedback capacitor.

An equalizer circuit and related power management circuit are provided. The power management circuit includes a voltage amplifier circuit configured to generate an envelope tracking (ET) voltage based on a differential target voltage and provide the ET voltage to a power amplifier circuit(s) via a signal path for amplifying a radio frequency signal(s). An equalizer circuit is provided in the power management circuit to equalize the differential target voltage prior to generating the ET voltage. Specifically, the equalizer circuit is configured to provide a transfer function including a second-order complex-zero term and a real-zero term for offsetting a transfer function of an inherent trace inductance of the signal path and an inherent impedance of the voltage amplifier circuit. By employing the second-order transfer function with the real-zero term, it is possible to reduce distortion in the ET voltage, especially when the RF signal(s) is modulated in a wide modulation bandwidth.

An amplifier comprising a gain stage with a feedback network comprising two ports between which at least three capacitors are connected in series and between each pair of capacitors a resistor is connected to a predetermined voltage. The gain stage is provided in a feedback loop over a primary amplifier.

A signal output circuit includes an inverting amplifier circuit, a feedback capacitor and a low pass filter. The inverting amplifier circuit includes an input terminal and an output terminal. The inverting amplifier circuit executes an inverting amplification based on an input signal to output a signal to the output terminal at a pull-up state. An output stage of the inverting amplifier circuit is an open collector or an open drain. The feedback capacitor is connected between the input terminal and the output terminal of the inverting amplifier circuit. The low pass filter has an input and an output. The input of the low pass filter is connected to the output terminal of the inverting amplifier. The output of the low pass filter is connected to the feedback capacitor.

An amplifier comprising a gain stage with a feedback network comprising two ports between which at least three capacitors are connected in series and between each pair of capacitors a resistor is connected to a predetermined voltage. The gain stage is provided in a feedback loop over a primary amplifier.

A variable-current trans-impedance amplifier (TIA) for an ultrasound device is described. The TIA may be coupled to an ultrasonic transducer to amplify an output signal of the ultrasonic transducer representing an ultrasound signal received by the ultrasonic transducer. During acquisition of the ultrasound signal by the ultrasonic transducer, one or more current sources in the TIA may be varied. The variable-current trans-impedance amplifier may include multiple stages, including a first stage having N-P transistor pairs configured to receive an input signal and produce a single-ended amplified signal.

An error amplifier including a differential pair circuit, a resistive device, a low voltage capacitor, and a protection device. The differential pair circuit is coupled between an upper supply node and a lower supply node with first and second intermediate nodes and is responsive to a difference between a reference voltage and a feedback voltage for driving a control voltage developed on the second intermediate node. The resistive device is coupled between the second intermediate node and a low voltage node, and the low voltage capacitor and the protection device are coupled between the low voltage node and the lower supply node. The protection device is dynamically controlled by the first intermediate node to prevent the low voltage node from exceeding a predetermined maximum level. The protection device may be a transistor having size parameters based on voltage characteristics of the first intermediate node during expected operating conditions.