Patent ID: 6359512
Filing Date: 2002-03-19
Classification: H03F

Abstract:
An operational amplifier comprising:(a) a differential input stage having first and second input conductors and first and second output conductors; (b) a class AB output stage including a pull-up transistor having an emitter coupled to a first supply voltage, a collector coupled to an output conductor, and a base coupled to a first terminal of a class AB control circuit, and a pull-down transistor having an emitter coupled to a second supply voltage, a collector coupled to the output conductor, and a base coupled to a second terminal of the class AB control circuit; (c) a gain stage having an input coupled to at least one of the first and second output conductors of the differential input stage, the gain stage having an output coupled to the second terminal of the class AB control circuit; (d) a slew rate boost circuit including i. a first unbalanced differential amplifier having a first input coupled to the first input conductor and a second input coupled to the second input conductor and also having first and second output conductors, and a second unbalanced differential amplifier having a first input coupled to the first input conductor and a second input coupled to the second input conductor and also having first and second output conductors, ii. a first boost amplifier having first and second inputs coupled to the first and second outputs, respectively, of the first unbalanced amplifier, and a second boost amplifier having first and second inputs coupled to the first and second outputs, respectively, of the second unbalanced amplifier, iii. first and second transistors each having a base coupled to an output of the first boost amplifier, the first transistor having an emitter coupled to the second output of the first unbalanced amplifier and a collector coupled to the first supply voltage, the second transistor having an emitter coupled to the second supply voltage and a collector coupled to the second terminal of the class AB control circuit, iv. third and fourth transistors each having an emitter coupled to the first supply voltage and a base coupled to an output of the second boost amplifier, the third transistor having a collector coupled to the first output of the second unbalanced amplifier, the fourth transistor having a collector coupled to the first terminal of the class AB control circuit.