Operational amplifier output stage and method

A method of operating an amplifier output stage to reduce power dissipation during peak output currents, the method comprising:

• (a) providing a first output transistor having a first electrode coupled to a first supply rail and a control electrode coupled to receive a first voltage signal and a first output cascode transistor having a first electrode coupled to a second electrode of the first output transistor and a second electrode coupled to an output conductor conducting an output signal;
• (b) controlling a voltage on a control electrode of the first output cascode transistor in response to a first control signal on a first electrode of the first output cascode transistor by applying the first control signal to a control electrode of a first input transistor of an input stage of a first control amplifier, the input stage of the first control amplifier including an active load transistor, a second electrode of the first input transistor of the input stage of the first control amplifier being coupled to a first electrode of the active load transistor of the input stage of the first control amplifier;
• and
• (c) controlling a voltage on a control electrode of the active load transistor of the input stage of the first control amplifier in response to the first control signal in accordance with a current produced in the first output transistor in response to the first voltage signal.

An amplifier output stage having reduced power dissipation during peak output currents, comprising:

• (a) a first output transistor having a first electrode coupled to a first supply rail and a control electrode coupled to receive a first voltage signal and a first output cascode transistor having a first electrode coupled to a second electrode of the first output transistor and a second electrode coupled to an output conductor conducting an output signal;
• and
• (b) circuitry for controlling a voltage on a control electrode of the first output cascode transistor in response to a control signal on a first electrode of the first output cascode transistor, the control circuitry including
• i. means for applying the control signal to a control electrode of an input transistor of an input stage of a control amplifier, and
• ii. means for controlling an active load transistor in response to the control signal, a second electrode of the first input transistor being coupled to a first electrode of the active load transistor to boost the magnitude of the voltage on the control electrode of the first output cascode transistor in response to a large current flowing through the first output cascode transistor.