High ratio current source

摘要

A current source circuit includes at least three pairs of bipolar transistors of the same polarity type. The first transistors of each pair are connected in one series circuit string emitter to collector. The second transistors of each pair are connected in another circuit string. The first-pair second transistor is connected emitter to collector with the second-pair second transistor while the emitter of the second-pair second transistor is connected to the base of the third-pair second transistor which serves as the output transistor. The first transistors of the first and third pairs have their bases connected respectively with their collector. The bases of the two second-pair transistors are cross coupled with the collectors of the second-pair transistors. With an input current applied to the collector of the first first-pair transistor the output current may be many times greater than the input current depending upon the relative base-emitter junction areas of the six transistors, and the high current ratio is relatively independent of the transistor current gains.