High swing output circuit having differential to single-ended conversion and method

An amplifier output circuit comprising:

• a level shifting circuit configured to receive a differential input signal having first and second components, said level shifting circuit defining a first current path controlled by the first component of the differential input signal and a second current path controlled by the second component of the differential input signal, first and second transistors coupled in series with the first and second current paths, respectively, and first and second resistors coupled intermediate the first and second transistors, respectively, and a first power supply rail;
• a driver stage including a third transistor having a base coupled to the first current path at a node intermediate the first transistor and a second power supply rail, a fourth transistor having a base coupled to an emitter of the third transistor and a fifth transistor having a base coupled to the second current path at a node intermediate the second transistor and the second power supply rail;
• and
• an output stage including a sixth transistor having an emitter coupled to the second power supply rail, a collector coupled to an amplifier output and a base coupled to a collector of the fourth transistor so that the fourth transistor collector conducts at least part of a base drive current of the sixth transistor and a seventh transistor having a base coupled to an emitter of the fifth transistor, an emitter coupled to the first power supply rail and a collector coupled to the amplifier output.

An amplifier output circuit comprising:

• a first transistor having an emitter coupled to a first power supply rail and a collector coupled to an amplifier output;
• a second transistor having an emitter coupled to a second power supply rail and a collector coupled to the amplifier output;
• a third transistor having a base connected to receive a first component of a differential input signal;
• a fourth transistor having a base coupled to an emitter of the third transistor and an emitter coupled to the second power supply rail and a collector coupled to a base of the first transistor so that the collector of the fourth transistor conducts at least part of a base current of the first transistor;
• and
• a fifth transistor have a base connected to receive a second component of the differential input signal and an emitter coupled to a base of the second transistor.

A method of current limiting an amplifier output stage capable of providing a sourcing output current from a first transistor of the output stage and a sinking output current from a second transistor of the output stage, with the first and second transistors having collectors coupled to an output of the output stage and third and fourth transistors connected to drive the first and second output transistors, respectively, said method comprising:

• switching the fourth transistor from a conductive to a substantially non-conductive state in response to an increase in the sourcing output current;
• limiting a base-emitter voltage of the third transistor to a maximum value in response to the change in the fourth transistor from a conductive to a substantially non-conductive state so as to limit the sourcing output current;
• switching the third transistor from a conductive to a substantially non-conductive state in response to an increase in the sinking output current;
• and
• limiting a base-emitter voltage of the fourth transistor to a maximum value in response to the change in state of the third transistor from a conductive to a substantially non-conductive state so as to limit the sinking output current.