An embodiment includes a track and hold amplifier device. A device may include an emitter follower transistor coupled to each of an input and an output. The device may also include a charging node coupled between the output and a voltage supply, wherein the charging node is also coupled to the input via the emitter follower transistor. Further, the device may include a cascode switch coupled to each of the input and the output. The cascode switch may be configured to cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode. The cascode switch may also be configured to cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode. The cascode switch may include a MOS-HBT transistor combination operating in class AB mode.

Provided is an interpolation operational amplifier circuit, including: at least two sets of differential input pair transistors, each differential input pair transistor including first and second transistors, wherein base terminals of the first and second transistors are electrically connected to serve as a base terminal of the differential input pair transistor, and source electrodes of the first and second transistors are electrically connected to serve as a source electrode of the differential input pair transistor; and a voltage control unit electrically connected to the base terminal and source electrode of the differential input pair transistor, and configured to control a voltage of the base terminal of the P-type differential input pair transistor to be smaller than the first power supply voltage, and/or to control a voltage of the base terminal of the N-type differential input pair transistor to be larger than the second power supply voltage.

Provided is an interpolation operational amplifier circuit, including: at least two sets of differential input pair transistors, each differential input pair transistor including first and second transistors, wherein base terminals of the first and second transistors are electrically connected to serve as a base terminal of the differential input pair transistor, and source electrodes of the first and second transistors are electrically connected to serve as a source electrode of the differential input pair transistor; and a voltage control unit electrically connected to the base terminal and source electrode of the differential input pair transistor, and configured to control a voltage of the base terminal of the P-type differential input pair transistor to be smaller than the first power supply voltage, and/or to control a voltage of the base terminal of the N-type differential input pair transistor to be larger than the second power supply voltage.

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.

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.

An embodiment includes a track and hold amplifier device. A device may include an emitter follower transistor coupled to each of an input and an output. The device may also include a charging node coupled between the output and a voltage supply, wherein the charging node is also coupled to the input via the emitter follower transistor. Further, the device may include a cascode switch coupled to each of the input and the output. The cascode switch may be configured to cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode. The cascode switch may also be configured to cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode. The cascode switch may include a MOS-HBT transistor combination operating in class AB mode.

A power amplifier system includes a differential power amplifier and a bias circuit. The differential power amplifier is arranged for receiving a differential input pair to generate an output signal. The bias circuit is arranged for generating a bias voltage to bias the differential power amplifier, and the bias circuit comprises a source follower for receiving a reference voltage to generate the bias voltage.

A power amplifier system includes a differential power amplifier and a bias circuit. The differential power amplifier is arranged for receiving a differential input pair to generate an output signal. The bias circuit is arranged for generating a bias voltage to bias the differential power amplifier, and the bias circuit comprises a source follower for receiving a reference voltage to generate the bias voltage.