US2313014A - Anticoupled amplifier - Google Patents

Description

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March 2, 1943. w. HAGEN ANTI-COUPLED AMPLIFIER Filed May 23, 1940 Figi Figa

Patented Mar. 2, 19143 AN'rIcoUrLEn AMPLIFIER Wolfgang Hagen, Berlin, Germany; vested in the Alien Property Custodian Application May 23, 1940, Serial No. 336,777

In Germany April 6, 1 939 3 Claims.

This invention relates to amplifiers in which distortions are obviated by negative reaction or so-called anti-coupling, and it aims to improve the function of these devices.

The invention will be understood from the following description and be particularly pointed out in the appended claims, reference being had to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing a known arrangement; Fig. 2 is a diagram representing one embodiment of the invention; while Fig. 3 is a view similar to Fig. 2 and illustrating a completion of the arrangement there disclosed.

In all of these figures A denotes an amplifier of any suitable construction and whose output resistance is designated Ra. U1 denotes an input transformer, while U2 designates an output transformer for this amplifier.

Amplifiers of the kind referred to require the terminal resistances of the input and output circuits not to affect the negative reaction, since otherwise the amplifiers may be caused to sing in case of varying the terminal circuits thereof. The input circuit vof prior devices is a bridge connection of the kind shown in Fig. '1. arrangement comprises resistances W1, W2, Ws, W4. These, however, must be high enough to prevent the transformer U1 from being attenuated too much. As a result the/earth capaci# ties C1, C2 of the transformer, which are indicated by dotted lines, affect the' phase of the negative reaction path, especially in the case of high frequencies. Such undesired changes in phase, however, should as far as `possible be kept out of the negative reaction path, since they can cause the amplifier to sing and can be compensated only by complicated phase networks.

According to the invention, as shown in Fig. 2, transformer U1 comprises two symmetrical windings a, b and a, c, loaded with resistances R1, R2. of the two windings. The center point or point of symmetry between the resistances R1, R2 is designated e. These resistances are calculated to provide for a suitable condition of the input circuit but may be high to some extent. The reaction current flowing from. d to a passes through the windings a, b and a, c in opposite directions. The two current components thus produced are equal to one another, whereby there will be no reaction voltage arising at winding b, c. The capacity of the windings of transformer 'Ui is in parallel with the resistances R4, Rs. These, however, are made so low as not to affect the phase of ,the reaction circuit. At Ri This a' is the -center' point or point of symmetry the same reaction voltage arises as at Rz. To resistance R1 the amplifier input circuit is connected by high ohmic means (not shown). In

-case such a connection cannot be provided an equivalent simulation of the input circuit should be joined in parallel with resistance R2.

This arrangement of the input circuit enables the amplifier to be adjusted simply by varying the negative reaction. Such variation may be effected by means of resistances Re, Rv, Fig. 3. which constitute a potentiometer effective with respect to the reaction voltage. R7 is a low ohmic resistance. Adjusting this potentiometer causes the degree of reaction, that is, the amplication, to be regulated in its turn.

While the invention has been described and illustrated in connection with two specific embodiments, it is to be understood that various changes may be made therein as will occur to those skilled in this art, and that the invention is not limited to the .two forms shown by way of example, except as may be required by the claims which follow. I

What is claimed is:

1. An input circuit for a negative feed-'back amplifier, comprising a transformer, a secondary therefor comprising a pair of symmetrical wind ings connected in series, a pair of loading resistances connected inY series and shuntedacross the outer terminals of said windings, a circuit to ground connected to the junctiorrpoint of said resistances, a circuit connecting the terminals of one of said resistances to the input of the amplifier, and a negative feed-back circuit from said amplifier connected to the junction` point of said windings.

2. An amplifier comprising input and output terminals, an input circuit therefor comprising a transformer, a secondary therefor comprising a pair of symmetrical windings connected in series, a pair of loading resistances connected in series and shunted across the outer terminals of said windings, a pair of resistances connected in series and shunted across the output terminals of said amplier, a feedback circuit; including a resistance, connected between the junction point of the last mentioned resistances and the junction point of said windings, means for controlling the amount of feedback comprising a resistance connected between the junction of said windings and the junction point of said loading resistances, and circuits connecting the input termifials of said amplifier to opposite terminals of one of said loading resistances.

3. An amplifier comprising input and output terminals, an input circuit therefor comprising a transformer, a secondary therefor comprising a pair of symmetrical windings connected in series, a pair of loading resistances connected in series and shunted across the outer terminals of said windings, a pair of resistances connected in series and shunted across the output terminals of said amplifier, a feed-back circuit including a. resistance for regulating the amount of feed-

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