Patent ID: 6262633
Filing Date: 2001-07-17
Classification: H03F

Abstract:
An operational amplifier output stage, comprising:complementary bipolar output transistors, the collector-emitter circuits of which are connected in series between a first supply voltage and a second supply voltage, the junction between said collector-emitter circuits being said output stage's output terminal, said output transistors connected to conduct respective currents in response to complementary drive signals with the difference current between said respective currents delivered to said output terminal as said output stage's output current,a drive circuit connected to provide said complementary drive signals to the bases of said output transistors, said drive circuit arranged to receive an output stage input signal at an output stage input and to conduct components of said complementary drive signals through first and second current paths, the magnitude of said complementary drive signals varying with said output stage input signal, said drive circuit having a given quiescent current which limits the maximum amplitude of said drive signals,first and second complementary bipolar clamp transistors biased with respective bias voltages, said clamp transistors connected to the bases of respective output transistors to set the quiescent current of said output transistors and to prevent said output transistors from being cut off, andfirst and second transistors connected to mirror the currents in said first and second current paths, the collectors of said first and second transistors connected to the bases of their opposing output transistors such that each provides an additional base drive path for its output transistor, said additional base drive paths reducing the amplitudes of the drive signals needed from said drive circuit for a given output current and thereby decreasing the amount of distortion that would otherwise be introduced into said output current by said drive circuit.