Amplifier circuit and method

An operational amplifier, comprising:

• an input amplifier stage having an output;
• a bipolar junction transistor for sourcing current to an external load;
• a bipolar junction transistor for sinking current from the external load, a collector of said sourcing transistor coupled to a collector of said sinking transistor to form a common output node;
• a mirroring bipolar junction transistor having a base coupled to a base of said sinking transistor such that current in said sinking transistor approximately mirrors current in said mirroring transistor;
• a current balancing circuit responsive to said mirroring transistor and coupled to control current flow through said sourcing transistor over a prescribed range;
• said mirroring transistor operable to draw current from said balancing circuit in response to a first predetermined output from the input amplifier stage such that said balancing circuit causes an insignificant current to flow in said sourcing transistor and said mirroring circuit operable to cause said sinking transistor to sink a significant current from the external load;
• and
• said mirroring transistor operable to draw an insignificant current from said balancing circuit in response to a second predetermined output from the input amplifier stage such that said balancing circuit causes a significant current to flow in said sourcing transistor.

A method for controlling an output current of an amplifier circuit having sourcing and sinking circuits coupled to a common output node, said method comprising the steps of:

• generating a control output signal from an input amplifier stage of the amplifier circuit in response to an input to the amplifier circuit;
• providing the control signal to the sinking circuit and to a mirror circuit that mirrors an output current;
• drawing current from a current balancing circuit in response to a first predetermined output of the amplifier stage such that the balancing circuit causes an insignificant current to flow in the sourcing circuit and significant current flow in the sinking circuit;
• and
• drawing an insignificant current from said balancing circuit in response to a second predetermined output from the amplifier stage such that the balancing circuit causes a significant current to flow in said sourcing circuitry, said balancing circuit being responsive to said mirroring circuitry and operable to control current flow through the sourcing circuitry over a prescribed range.