Abstract: A three terminal current gain cell is made up of a three-stage common emitter high gain amplifier configuration using complementary transistors. A controlled percentage of the output is coupled back to the input to provide negative feedback. The emitters of the complementary devices are coupled to the appropriate terminals that comprise the cell output. One of the devices employs a dual ratioed collector with the smaller of the two collectors being made to track the input current due to the feedback condition. Thus, the current gain of the cell is determined by a geometric ratio. The gain can be further multiplied by employing additional ratioed devices within the cell or by cell cascading. In one application, the current gain cell is combined with a photo sensor providing the input current. This produces a two terminal device that passes a current linearly related only to the illumination level over a very large range of illumination and other ambient conditions.

Abstract: The disclosed amplifier includes first and second transistors each having an emitter coupled to a bias source, a base, a first collector and a second collector. A third transistor has a collector connected to another bias source, an emitter connected to the base of the first transistor and to the first collector of the second transistor, and a base for receiving input signals. A fourth transistor has a collector connected to another bias source, an emitter connected to the base of the second transistor and to the first collector of the first transistor, and a base for receiving second input signals. Any difference in voltage between the input signals is indicated by an imbalance in current through the second collectors of the first and second transistors. The first collectors of these transistors provide positive feedback for amplifying the magnitude of this imbalance.