Amplifier active load

Details Amplifier active load Amplifier active load

1985-03-25

1986-12-16

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330260, H03F 345

Patent

active

046299971

ABSTRACT:
The present invention is an improved active load which eliminates the current imbalance between the collectors of the emitter-coupled input transistors. The circuit includes a pair of first and second emitter-coupled transistors with their collectors coupled to a current source which supplies substantially equal currents to the collectors of the two transistors. The collector of one of the emitter-coupled transistors is coupled to the base of a third output transistor. A fourth transistor is coupled between the collector of the output transistor and the supply voltage. Finally, the circuit includes means for supplying the base current to the fourth transistor such that the base current of the fourth transistor and the third output transistor are substantially equal and the collector currents of the first and second emitter-coupled transistors remain substantially equal, resulting in negligible offset current and high open loop gain. Preferably, this is done by coupling the base of the fourth transistor to the collector of the first emitter-coupled transistor while the base of the output transistor is coupled to the collector of the second emitter-coupled transistor.

REFERENCES:
patent: 3916331 (1975-10-01), Schenck

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