Amplifier circuit

In a current mirror amplifier having an input terminal, an output terminal, a common terminal, and first and second transistors of a first conductivity type, each of said first and second transistors having base and emitter and collector electrodes and an associated transconductance and having a current gain substantially equal to (.beta.+1) between its base and emitter electrodes, (.beta.+1) being a positive number larger than unity, their emitter electrodes being direct current conductively connected to said common terminal, the collector electrodes of said first and second transistors being direct current conductively connected respectively to said input terminal and said output terminal, and the base electrodes of said first and said second transistors being connected to said input terminal, means for compensating against the problem of the current gain of said current mirror amplifier as between its input and output terminals undesirably departing, due to base currents flowing through said input terminal and not through said output terminal, from a value equal to a ratio of the transconductances of said first and second transistors, which means comprises:

• a third transistor of said first conductivity type having a base electrode connected to said output terminal, having a collector electrode coupled to a terminal to which an operating voltage may be applied, having an emitter electrode, and having a current gain of (.beta.+1) between its base and emitter electrodes;
• and
• means having an input circuit connected to receive current flow through the common terminal of said current mirror amplifier and having an output circuit connected for applying a substantially like-valued current to the emitter electrode of said third transistor in the forward direction, thereby to cause the desired compensating current flow through the base electrode of said third transistor.

A current mirror amplifier comprising:

• input, output and common terminals;
• first, second and third transistors of the same conductivity type, and current gain characteristics, each having base, emitter and collector electrodes and an associated transconductance, said first and said second transistors having their respective transconductances related in a 1:G ratio, the collector electrodes of said first and said second transistors being direct current conductivity connected respectively to said input terminal and to said output terminal, the base electrodes of said first and said second transistors having an interconnection between them to which each of them and said input terminal are direct current conductively connected, the emitter electrodes of said first and said second transistors having an interconnection between them to which each of them and the collector electrode of said third transistor is direct current conductively connected, the emitter electrode of said third transistor being direct current conductively connected to said common terminal;
• means providing direct coupled collector-to-base feedback to said third transistor for adjusting its base current to condition it to accept substantially all of the combined emitter currents of said first and said second transistors as its collector and base currents;
• and
• means responsive to said base current of said third transistor for adding a current substantially equal to said base current of said third transistor to the collector current of said second transistor at said output terminal, whereby the current gain of said current mirror amplifier as between its input and output terminals which is substantially equal in magnitude to said 1:G ratio is made still more nearly so.

In a current mirror amplifier having an input terminal, an output terminal, a common terminal, and first and second transistors of a first conductivity type, each of said first and second transistors having base and emitter and collector electrodes and an associated transconductance and having a current gain substantially equal to (.beta.+1) between its base and emitter electrodes, (.beta.+1) being a positive number larger than unity, their emitter electrodes being direct current conductively connected to said common terminal, the collector electrodes of said first and second transistors being direct current conductively connected respectively to said input terminal and said output terminal, and the base electrode of said first and said second transistors being connected to said input terminal, means for compensating against the problem of the current gain of said current mirror amplifier as between its input and output terminals undesirably departing, due to base currents, flowing through said input terminal and not through said output terminal, from a value equal to a ratio of the transconductances of said first and second transistors, which means comprises:

• means having an input circuit connected to receive the current flow through the common terminal of said current mirror amplifier as corresponds to the combined emitter currents of said first and second transistors, and having an output circuit connected to said output terminal, the output circuit of said means responsive to current received by the input circuit of said means to demand a current 1/(.beta.+1) times as large.