Current amplifier

Abstract

A three-terminal current amplifier has a current gain substantially independent of the forward current gains of its component transistors. It employs a first transistor with collector-to-base feedback regulating its collector current flow to equal applied input current and a second transistor having a base emitter circuit in parallel with that of the first transistor. Output current from the collector electrode of the second transistor consequently is proportional to the input current. Means are provided for maintaining the collector potentials of the first and second transistors substantially equal to help maintain a fixed relationship between the output and input current amplitudes.

What is claimed is: 
     
       1. In a current amplifier which includes input, common and output terminals; a first and a second transistors of like conductivity type having their emitter electrodes direct current conductively coupled via said common terminal to a reference potential, each having a base electrode and having their collector electrodes respectively connected by first and second direct current conductive coupling paths respectively to said input terminal and to said output terminal; means for regulating collector current flow of said first transistor to be substantially equal to input current received at said input terminal, said means including similar direct coupling of said input terminal to each of said base electrodes of said first and said second transistors; and means for receiving output current flow connected to said output terminal, said output current flow substantially equal to the collector current flow of said second transistor, the improvement comprising: a third transistor of the same conductivity type as said first and second transistors, said third transistor having a base electrode and having an emitter electrode-to-collector electrode path, said second direct current conductive coupling path comprising said emitter electrode-to-collector electrode path connected in a sense to conduct the collector-to-emitter current of said second transistor; and   means for maintaining the collector electrodes of said first and second transistors at substantially the same potential, comprising means .[.coupled to the.]. .Iadd.connected between the collector electrode of said first transistor and the .Iaddend.base electrode of said third transistor for establishing .[.it.]. .Iadd.the base electrode of said third transistor .Iaddend.at a potential which differs from that at the collector electrode of said first transistor by an amount substantially equal to that between the base electrode of said third transistor and the collector electrode of said second transistor.   
     
     
       2. The combination of: a two-transistors current amplifier, each transistor having a base, an emitter and a collector, said bases being connected to one another and said emitters being connected to a point of reference potential, and said amplifier including a negative feedback connection between said bases and the collector of the first of said transistors;   an input terminal;   an output terminal;   a first diode connected in the forward direction between said input terminal and the collector of the first of said transistors; and   a second diode connected in the forward direction between said input terminal and the collector of the second of said transistors.   
     
     
       3. .[.A circuit as set forth in claim 2 wherein said second diode comprises the base-emitter diode of a third transistor of the collector of which connects to said output terminal..]. .Iadd.The combination of: a two-transistor current amplifier, each transistor having a base, an emitter and a collector, said bases being connected to one another and said emitters being connected to a point of reference potential, and said amplifier including a negative feedback connection between said bases and the collector of the first of said transistors;   an input terminal;   an output terminal;   a first diode connected in the forward direction between said input terminal and the collector of the first of said transistors;   a second diode connected in the forward direction between said input terminal and the collector of the second of said transistors wherein said second diode comprises the base-emitter diode of a third transistor the collector of which connects to said output terminal. .Iaddend.   
     
     
       4. A circuit as set forth in claim 2 wherein said feedback connection comprises a direct conductive connection. 
     
     
       5. .[.In a current amplifier as set forth in claim 1, said means for maintaining the collector electrodes of said first and second transistors at substantially the same potential comprising: a connection from said base electrode of said third transistor to said input terminal; and   semiconductor diode means in said first direct current conductive coupling path, connected to conduct the collector current of said first transistor in the forward direction..]. .Iadd.In a current amplifier which includes input, common and output terminals; a first and a second transistors of like conductivity type having their emitter electrodes direct current conductively coupled via said common terminal to a reference potential, each having a base electrode and having their collector electrodes respectively connected by first and second direct current conductive coupling paths respectively to said input terminal and to said output terminal; means for regulating collector current flow of said first transistor to be substantially equal to input current received at said input terminal, said means including similar direct coupling of said input terminal to each of said base electrodes of said first and said second transistors; and means for receiving output current flow connected to said output terminal, said output current flow substantially equal to the collector current flow of said second transistor, the improvement comprising:   a third transistor of the same conductivity type as said first and second transistors, said third transistor having a base electrode and having an emitter electrode-to-collector electrode path, said second direct current conductive coupling path comprising said emitter electrode-to-collector electrode path connected in a sense to conduct the collector-to-emitter current of said second transistor; and   means for maintaining the collector electrodes of said first and second transistors at substantially the same potential, comprising means coupled to the base electrode of said third transistor for establishing it at a potential which differs from that at the collector electrode of said first transistor by an amount substantially equal to that between the base electrode of said third transistor and the collector electrode of said second transistor said means for maintaining the collector electrodes of said first and second transistors at substantially the same potential comprising: a connection from said base electrode of said third transistor to said input terminal; and   semiconductor diode means in said first direct current conductive coupling path, connected to conduct the collector current of said first transistor in the forward direction. .Iaddend.     
     
     
       6. In a current amplifier as set forth in claim 5, said semiconductor diode means comprising: a fourth transistor having base, emitter and collector electrodes, of the same conductivity as the remaining transistors, and connected collector electrode to base electrode so that it operates as a diode.