Transistor amplifier of the Darlington type with internal bias providing low offset voltage and offset current drift

摘要

A transistor amplifier of the Darlington type, in which successive transistors have their collectors connected in common and in which the emitter of the first transistor is connected to the base of the second transistor, is characterized by a source of bias current for the first transistor which tends to suppress variations in transistor current gain and which permits the Darlington amplifier to operate in differential configurations with low offset voltage drift and low offset current drift. The bias current source is arranged to direct between the emitter of the first transistor and the emitter of the second transistor a bias current which is a predetermined fraction, e.g., one-tenth, of the collector current of the second transistor, thereby stabilizing the operation of the first transistor. The bias current source is formed in one case by a second collector region arranged in the second transistor with a size selected to provide the predetermined fraction of collector current and connected to the emitter of the first transistor. In another case, the bias current source is formed by a third transistor having its emitter and base connected in common with the emitter and base of the second transistor and having its collector connected to the emitter of the first transistor, the third transistor having its size selected in relation to the size of the second transistor to carry the predetermined fraction of the collector current of the second transistor.