Feed-forward amplifier

Abstract

A high-precision amplifier employs a feed-forward technique to provide a first order correction of amplifier distortion. A second amplifier is utilized to sense the base-to-emitter distortion of a main amplifier and develop an error output which is injected into an output node to provide cancellation of distortion from the output of the main amplifier. The feed-forward distortion-correction technique is particularly applicable to high-precision wideband differential amplifiers; however, the technique may be used in other amplifiers as well.

What I claim as being new is: 
     
       1. A feed forward amplifier, comprising: a main amplifier channel comprising a first emitter coupled pair of transistors for receiving an input signal and producing an amplified signal therefrom;   network means coupled to the bases and emitters of said first emitter coupled pair of transistors for producing distortion signals proportional to the distortion caused by the base-to-emitter junctions of said first pair of transistors;   a feed forward channel comprising a second emitter coupled pair of transistors for receiving said distortion signals and producing a correction signal therefrom; and   means for coupling the collectors of said first and second pairs of transistors together in algebraic summing relationship so that said correction signal is summed with said amplified signal to provide a substantially error-free output signal.   
     
     
       2. An amplifier in accordance with claim 1 wherein said network means includes a first pair of matched resistors coupled to the respective bases of said first pair of transistors and a second pair of matched resistors coupled to the respective emitters of said first pair of transistors, said first and second pairs of resistors being cross connected to provide at the junctures thereof said distortion signals. 
     
     
       3. An amplifier in accordance with claim 2 wherein said network means further includes semiconductor junction modeling means interposed between said first pair of resistors and said bases of said first pair of transistors to increase amplifier precision by modeling the distortion-producing mechanism.  .[.4. An amplifier in accordance with claim 1 wherein the bases of said second emitter coupled pair of transistors are coupled respectively to the collectors of said first emitter coupled pair of transistors, the collectors of said second pair of transistors being cross coupled to the collectors of said first pair of transistors for producing differential output signal currents by combining 
     
     
        said amplified signal with said correction signal..]. 5. An amplifier in accordance with claim 1 wherein the bases of said first emitter coupled transistors are connected to a bias current source and the bases of said second emitter coupled pair of transistors are coupled between the emitters of said first pair of transistors, the collectors of said second pair of transistors being cross coupled to the collectors of said first pair of transistors for producing differentially-matched output currents by combining said amplified signal with said correction signal. .Iadd. 6. A feed forward amplifier comprising: an emitter-coupled pair of input transistors having a predetermined resistance in the emitter path thereof;   a first pair of transistors connected in common-base configuration, the emitters of which are connected to respective collectors of said input transistors;   an emitter-coupled pair of correction transistors having a predetermined resistance in the emitter path thereof so as to match the gain of said correction transistors with said input transistors, the bases of said correction transistors being connected to respective collectors of said input transistors and the collectors thereof being cross-coupled to the respective collectors of said first pair of common-base transistors to provide collector-current summing nodes; and   a second pair of transistors connected in common base configuration to provide an output signal, the emitters of which are connected to respective collector current summing nodes. .Iaddend. .Iadd. 7. A feed forward amplifier, comprising:   a main amplifier channel comprising a first emitter coupled pair of transistors for receiving an input signal and producing an amplified signal therefrom;   a pair of common base amplifier transistors, the emitters of which are coupled respectively to the collectors of said first emitter coupled pair of transistors, said common base amplifier transistors having substantially identical semiconductor junction characteristics as said first emitter coupled pair of transistors;   a correction amplifier channel comprising a second emitter coupled pair of transistors, the bases of which are coupled respectively to the collectors of said first emitter coupled pair of transistors, and the collectors of which are cross coupled to the collectors of said common base amplifier transistors; and   means for matching the gain of said main amplifier channel and said correction amplifier channel. .Iaddend..Iadd. 8. A feed forward amplifier in accordance with claim 7 wherein said gain-matching means comprises a pair of substantially equal-value resistances, one of which is disposed in the emitter path of said first emitter coupled pair of transistors, and the other of which is disposed in the emitter path of said second emitter coupled pair of transistors. .Iaddend. .Iadd. 9. A feed forward amplifier in accordance with claim 7 further comprising a second pair of common-base amplifier transistors, the emitters of which are coupled respectively to the collectors of the first-mentioned pair of common-base amplifier transistors. .Iaddend.