A buffer amplifier comprises a source follower and a feedback amplifier. The feedback amplifier may be configured to control a drain current of the source follower to remain substantially constant independent of a load.

Described herein is an apparatus and system of a low-impedance reference voltage generator. The apparatus comprises: a voltage-control loop including a first transistor to provide an output voltage; and a current-control loop to sense current through the first transistor, relative to a reference current. The node having the output voltage is a low-impedance node.

A multi-stage device includes multiple stages such as a first stage and a second stage. During operation, the first stage receives an input signal and outputs an intermediate signal based on the input signal. The second stage is coupled to the first stage to receive the intermediate signal and produce an output signal. According to one configuration, the second stage includes: i) a transistor, and ii) a circuit path between the first stage and the transistor. The transistor component is controlled to derive the output signal from the intermediate signal inputted to the circuit path.

A buffer amplifier comprises a source follower and a feedback amplifier. The feedback amplifier may be configured to control a drain current of the source follower to remain substantially constant independent of a load.

In accordance with an embodiment, a circuit includes: a first super source follower; a compensation circuit having a compensating node configured to provide a voltage of opposite phase of a voltage of an internal node of the first super source follower; and a first compensation capacitor coupled between an input of the first super source follower and the compensating node of the compensation circuit.

In accordance with an embodiment, a circuit includes an amplifier and a programmable capacitor coupled between an output of the first non-inverting and the input of the first amplifier.

In accordance with an embodiment, a circuit includes: a first super source follower; a compensation circuit having a compensating node configured to provide a voltage of opposite phase of a voltage of an internal node of the first super source follower; and a first compensation capacitor coupled between an input of the first super source follower and the compensating node of the compensation circuit.

An embodiment amplifier circuit includes a pair of subcircuits that includes a first subcircuit and a second subcircuit, each of which includes a buffer amplifier and a feedback circuit that includes a feedback capacitor. The amplifier circuit also includes a pair of output terminals. The first subcircuit and the second subcircuit each generate a different output signal of a pair of output signals that includes a first output signal and a second output signal. The amplifier circuit is configured for receiving a positive differential input signal at the first subcircuit, receiving a negative differential input signal at the second subcircuit, and receiving the pair of output signals at the pair of output terminals. The amplifier circuit is also configured for transmitting the first output signal to the feedback circuit of the first subcircuit, and transmitting the second output signal to the feedback circuit of the second subcircuit.

A Doherty amplifier circuit includes a carrier amplifier that amplifies an input high frequency signal, a peak amplifier that amplifies an input high frequency signal, a first bias circuit that applies a bias to the carrier amplifier, a second bias circuit that applies a bias to the peak amplifier, and a control circuit that controls the second bias circuit on the basis of an input high frequency signal and a signal indicating a drive level of the carrier amplifier.

A first circuit unit of an audio amplifier includes a first emitter follower connected to an pre stage input terminal, a second emitter follower connected to an pre stage input terminal, a main transistor connected to an output path of the first emitter follower and an output path of the second emitter follower, a first resistor and a second resistor, which are series-connected between the output path of the first emitter follower and a DC voltage source, and a zener diode connected to a series-connection point between the first resistor and the second resistor. A second circuit unit has a circuit configuration that is complementary to the first circuit unit. A path leading to a collector of each transistor configuring the first and second emitter followers in one of the circuit units is connected to the series-connection point in the other circuit unit.