Output stage for an operational amplifier
AssigneeMotorola, Inc.
InventorRobert L. Vyne
Life of this patent
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Abstract
An operational amplifier includes an input stage, an output stage including first, second and third NPN output transistors, and an intermediate stage. The first NPN output transistor sources load current to an output terminal while the second and third output transistors sink load current therefrom. The output of the intermediate stage is coupled to the base of the third NPN transistor and, via a resistor, to the base of the second NPN transistor. A first Miller capacitor is coupled between the input of the intermediate stage and the amplifier's output terminal, and a second Miller capacitor is coupled between the base of the second NPN transistor and the output terminal.
Claims5
An operational amplifier for providing load current to an output terminal, comprising:
- an input stage;
- an output stage including first, second and third NPN output transistors, each having base, emitter and collector terminals, said first NPN output transistor having an emitter coupled to said output terminal for conducting load current thereto and a collector terminal for coupling to a first source of supply voltage, said second NPN output transistor having a collector coupled to said output terminal for sinking load current therefrom and an emitter for coupling to a second source of supply voltage, and said third NPN output transistor having a collector coupled to said output terminal and an emitter for coupling to said second source of supply voltage;
- at least a first emitter follower transistor having a base terminal coupled to the output of said input stage, a collector coupled to the base of said first NPN output transistor and an emitter coupled to the base of said third NPN output transistor;
- a first capacitor coupled between the output of said input stage and said output terminal;
- a resistor coupled between the emitter of said emitter follower transistor and the base of said second NPN output transistor;
- and
- a second capacitor coupled between the base of said second NPN output transistor and said output terminal, said first and second capacitors for stabilizing said amplifier.
Dependencies are inferred from the claim text.