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July 5, 1938. 2,122,748 H. MAYER FOUR-POLE DEVICE CONTAINING NONLINEAR’ RESISTORS Filed Feb. 12, 1956 F119. 2 - R lNVENTdR HANS wlgYER " BY//’§ .5?“ 5 Luv-“DY ATTORNEY Patented July 5, 1938 2,122,748 UNITED STATES PATENT OFFICE 2,122,748 FOUR-POLE DEVICE CONTAINING, NON LINEAR RESIST'ORS Hans Mayer, Berlin-Charlottenburg, Germany, assignor to Siemens & Halske, Aktiengesell schaft, Berlin, Germany, ‘a corporation of Germany Application February 12, 1936, Serial No. 63,590 In Germany February 2'7, 1935 2 Claims. The invention relates to a four-pole device hav ing non-linear properties. Such four-pole de vices are necessary for many purposes such as for instance for the limitation of amplitudes, for the suppression of small amplitudes, or for the non-linear reduction of distortion. Such four pole devices can also be utilized for purposes of blocking or control when using non-linear re sistors whose values can be controlled by means of a direct potential. If such a four-pole device is to be inserted in such a manner in the transmission system that desirable amplitude ranges will be transmitted while undesirable ranges are suppressed, it will 15 be of particular advantage .for many purposes if the normal impedance of such four-pole device is independent of the amplitude. The invention relates to amplitude ?lters having a constant ap parent resistance independent of the amplitude, 20 at least within a de?nite amplitudinal range. Out of the theory of the linear networks a group of four-pole devices has become known in whichythe wave resistance Z is given by the equation 25 values may consist of known non-linear resistors, preferably dry recti?ers or hot conductors. Combinations of two respective dry recti?ers with opposite current ?ow and connected in parallel or in series were found to be especially suited. The four-pole devices constructed in accord ance with the invention are preferably of the type of bridge ?lters in whose branches or di agonals the elements having reciprocal resistance values are inserted. It is obviously within the scope of the present invention to utilize in place of bridge ?lters, all equivalent four-pole devices such as for instance bridged T-cil'cuits, cross ?les or the like. In accordance with a further feature of the in 15 vention, in order to obtain the desired reciprocity of the resistors, the non-linear resistors are com bined with linear resistors. Suited for this pur pose is also the use of non-linear resistors having different properties, or the use of special biasing 20' potentials. If the four-pole devices are to have a desired dependence upon frequency, the non linear resistors are to be combined with resistors depending upon corresponding frequencies. Z = 1/Z1-Z2 and which has a real and constant value in the entire frequency range if reciprocal impedance values are chosen for the resistors Z1 and Z2. 30 Known examples of such four-pole devices are represented by cross ?les, bridge ?les, bridged T-circuits and the like. A bridge-?le network is of the type shown in Fig. 5; while a bridged T ?le network is of the type shown in Fig. 6. A cross-?le network is a four-pole device containing crosswise connected impedances. When consid ering the two input, and the two output, termi nals of a four-pole device, the crosswise im pedances are switched in between the upper in 40 put terminal and the lower output terminal on the one hand, and between the lower input terminal and the upper output terminal on the other hand. In accordance with the invention, an amplitude 45 ?lter with constant wave resistance is obtained by replacing in an equivalent manner the re sistors Z1 and Z2 by resistances having reciprocal resistance values with respect to the amplitude. In this way it is accomplished that the transmis 50 sion ratio varies with the amplitude, while the wave resistance however, remains wholly, or ap proximately constant. Through the selection of a suitable end resistor it will be possible also to obtain a constant apparent resistance. 55 (Cl. 178-44) The elements having reciprocal resistance By suitably dimensioning the non-linear re- > sistors it’ can be accomplished that the four-pole devices act either as amplitude limiting means whereby amplitudes above a de?nite value will be limited (amplitude low-pass) or that these four pole devices act as amplitude suppressing means whereby the amplitudes are blocked below a de?» nite limit (amplitude-high pass). Principally it is also possible to obtain four-pole devices adapt ed for a de?nite amplitudinal range only (ampli tude ?lter band) or which block certain ranges (amplitude blocking band). The ?gures serve for elucidating the subject matter of the invention, and show examples of embodiments thereof. In the drawing, Figs. 1 to 4 inclusive show in each case a diiferent em bodiment of the invention, and each embodiment being accompanied by a characteristic curve; Fig. 5 shows a bridge type of network employing the invention; Fig. 6 illustrates a bridge T-type network. Figures 1 and 2 show two resistors having reciprocal resistance values and which are independent of the amplitude. The one of them according to Figure 1 consists of two de tectors GI and G2 placed in parallel, and the other one according to Figure 2 is formed of a series connection of two detectors GI and G2. The detectors may be of the dry recti?er type. With this arrangement there will be obtained the symmetry of the resistor for positive and nega tive amplitudes required for the transmission of 55 2 2,122,748 alternating currents. In both cases the current flow through the two detectors takes place in op posite directions. The curves indicate the cor responding relationship between the resultant resistance R and the voltage U. The potential U is supplied to the recti?er combinations by the the case previously mentioned. However the resistors R1 and R2 may also be chosen in such manner that they are equal at direct current source shown in each of Figs. 1 to 4. When biasing the amplitude-dependent re in which all amplitudes above a desired limit sistors by means of auxiliary potentials the re sistance course can be varied at will within wide limits. Figures 3 and 4 show the manner of completing the arrangement according to Fig ures l and 2 for the purpose of shifting the de pendence upon amplitude to the outside of a desired amplitudinal range U0. The curves of Figs. 1 to 4 have been obtained by measuring the strength and voltage within the circuits repre sented; the resistance value R results as the quotient of strength and voltage, and is shown as a function of the potential U. By proper choice of the value of U0 and of the recti?er de vices themselves, it can be accomplished that the resistors according to Figures 1 and 2, or ?gures l3 Li 3 and 4 have reciprocal resistance values; in other words, that at the amplitudes to be con sidered there is: 2 13 various, and there is no more balance of the bridge. The damping for this amplitude scope will, therefore, be substantially smaller than for large amplitudes while differing greatly at small ampitudes. This results in an amplitude ?lter 10 will not be transmitted. Figure 6 shows an equivalent four-pole device in the form of a bridged T-circuit. Herein the four branches of the bridge are formed by the in-put and out-put resistor and by the two in ductances L. The non-linear elements R1 and R2 having reciprocal resistance values are placed between the diagonal points. In place of the two inductances, two equal ohmic resistors or two equal inductances not coupled to each other, may be employed. In this case, however, it is neces sary that the apparent resistance Z of these re sistors ful?lls the equation values. The terminals E and the terminals A are A further feature of the idea of the invention resides in that for instance the auxiliary po tentials indicated in Figures 3 and 4 are not ?xed but can be controlled. In transmission systems having two directions of transmission, such as four-wire lines, an amplitude ?lter inserted in the one direction of transmission may for in stance be so controlled by the transmission cur rent passing in the other direction, that it prac tically blocks all amplitudes thus acting as echo blocking means. What I claim is: 1. A four-pole network comprising a bridge placed at the end points of the bridge diagonals. circuit having input and output terminals, two The example of embodiment of the inventive idea shown in Figure 5 represents a four-pole device in the form of a bridge ?lter. It consists of two equal inductances L coupled to each other and forming two branches of a bridge. The ) other two branches contain the non-linear re sistors R1 and R2 having reciprocal resistance If now, the two non-linear resistor combinations of the bridge arms including reactances, and R1 and R2 are so dimensioned that they approxi the other two arms each including opposed rec ti?ers, the recti?ers in one arm being in series relation, and those in the other arm being in 40 mately equal each other for amplitudes below a de?nite limit value, these amplitudes cannot pass through the four~pole device. The higher ampli tudes will be subjected to a substantially lower damping since for these amplitudes the bridge 45 is not balanced. The apparent resistance of the four-pole device is independent of the amplitude for amplitudes above the blocking limit. The bridge is equalized within the amplitude scope for which the two recti?er combinations R1 and R2 are equal to each other. Due to this fact, the damping between the input E and the out put A is very high. Outside this amplitude scope, the resistances of the recti?er combinations are parallel relation. 2. In an alternating current transmission net work, input and output terminals, a pair of re actances connected between an input and an ‘ output terminal, a direct connection between the other input and output terminals, a pair of rectifiers in parallel and in opposed relation con nected to a point between the reactances and to the direct connection, and a pair of recti?ers 50 in series and in opposed relation connected across both reactances. HANS MAYER.