US2207962A - Negative feedback amplifier - Google Patents

Description

July 16, 1940. H. WERRMANN 'NEGATVE FEEDBACK AMPLIFIER Filed oct. 23, 1937 AMPLIFIER INVENTOR HELL/VUT PREM 4N/v BY ATTORNEY Patented July-16, y1940 PATENT OFFICE NEGATIVE FEEDBACK AIWPLIFIER Y Hellmut Werrmann, Berlin-Charlottenburg, Germany, assignor to Siemens & Halske, Aktien` gesellschaft, Berlin-Siemenstadt, Germany Application October 23, 1937,' Serial No. 170,563 In Germany December 3, 1.936

1 claim. (o1. 179-171) It is known that linearity of amplier circuits can be obtained by employing a negative feedback. To provide a possibly favorable linearity itl is desirable to render the degree of the negative 5 feedback as high as possible. This degree is limited by the appearance of natural oscillations. It has been proposed to extend this limit as far as possible by the use of additional stabilizing means. The stabilizing means are inserted in the feedback circuit and serve for influencing the phase angle and the 'damping in the coupling path such that the amplifier remains stable in case of a high degree of feedback. The additional stabilizing means are of rather complicated structure, if its stabilizing action is to be a considerable one.

In accordance with the present invention a more favorable exploitation of such known amplifier circuit is brought about in that the stabilizing means which shall not be dispensed with in the interest of the stability of the entire circuit, are so adapted vand dimensioned that they influence at the same time the frequency pattern of the amplifier in the desired manner. Additional means .which hitherto had to be provided for the purpose of reducing distortion are no w omitted, and the entire structure of the amplifier circuit will be simplified. It is especially suitable to compensate by an appropriate design ofv the stabilizing means the decrease of the degree of amplification caused at the limits of the transmission range due to the transformers provided at the input and output of the amplifier. These stabilizing means may, however, be utilized to compensate forthe distortions 35 caused by the transmission elements such as lines connected to the amplifier. n vAn amplifier tube V, of any construction, is shown in the drawing connected to the input circuits and output circuits across the transformers T1 and T2. The feedback path, containing as a stabilizing member a single (or several) bridged T-circuit, is coupled in the known manner with l the grid circuit and plate circuit of the amplifier across two bridge circuits B1 and B2. The bridged T-circuit consists of ohmic series resistors Z1 and Z2 and parallel resistors R and R1; the inductances L, L1, and the condensers C, C1. If care is taken by a proper design of the bridging element and of the parallel element, that for instance for the 5 lower frequencies the damping increases slowly within a suitable range, the degree of amplification will likewise increase for these frequencies, and the decrease caused by the transformers will therebybe compensated. A correspondingpatl0 tern of the amplification curve can be attained at the lupper frequency limit of the transmission range by meansof a corresponding stabilizing member necessary for stabilizing the amplifier at the high frequencies. In like manner, also, the 15 distortion produced by the connected transmission lines can be eliminated. However, the invention is especially suited for compensating .the distortions Acaused by the transformers, since this compensation can be accomplished without adj 20 ditional circuit means.

What is claimedis: In an amplifier system adapted to transmit a wide rang-e of frequencies of the type comprising Van amplifier having' aninput transformer and 25 an youtput transformer, a bridge network connected across the secondary of the input transformer, a bridge network connected across the primary of the output transformer, a degenerative feedback path connected between the two bridge 30 networks, said feedback path includinga netv work whose constants are chosen to compensate for the decrease of the degree of amplification caused at the limits of said range by said input and output transformers, and said" compensation network consisting of a pair of r-esistorsin series in said feedback patha series path of a condenser, resistor vand inductance connected between the junction of said resistors and ground, and a shunt path across said pair of series resistors comprising a condenser inductance and resistor in parallel toeach other.

W'ERRMANN.

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