US2122748A - Four-pole device containing nonlinear resistors - Google Patents

Description

July 5, 1938.

H. MAYER FOUR-POLE DEVICE CONTAINING NONLINEAR RESISTORS Filed Feb. 12, 1956 lNVENTdR HANS wlgYER BY .5 5 Lu ATTORNEY Patented July 5, 1938 UNITED STATES PATENT OFFICE FOUR-POLE DEVICE CONTAINING NON- LINEAR RESIST'ORS 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 having non-linear properties. Such four-pole devices 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 fourpole devices can also be utilized for purposes of blocking or control when using non-linear resistors 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 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 filters having a constant apparent resistance independent of the amplitude, at least within a definite amplitudinal range.

Out of the theory of the linear networks a group of four-pole devices has become known in which the wave resistance Z is given by the equation 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. Known examples of such four-pole devices are represented by cross files, bridge files, bridged T-circuits and the like. A bridge-file network is of the type shown in Fig. 5; while a bridged T- file network is of the type shown in Fig. 6. A cross-file network is a four-pole device containing crosswise connected impedances. When considering the two input, and the two output, terminals of a four-pole device, the crosswise impedances 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 filter with constant wave resistance is obtained by replacing in an equivalent manner the resistors Z1 and Z2 by resistances having reciprocal resistance values with respect to the amplitude. In this way it is accomplished that the transmission ratio varies with the amplitude, while the wave resistance however, remains wholly, or approximately constant. Through the selection of a suitable end resistor it will be possible also to obtain a constant apparent resistance.

The elements having reciprocal resistance values may consist of known non-linear resistors, preferably dry rectifiers or hot conductors. Combinations of two respective dry rectifiers with opposite current fiow and connected in parallel or in series were found to be especially suited.

The four-pole devices constructed in accordance with the invention are preferably of the type of bridge filters in whose branches or diagonals the elements having reciprocal resistance values are inserted. It is obviously within the scope of the present invention to utilize in place of bridge filters, all equivalent four-pole devices such as for instance bridged T-cil'cuits, cross files or the like.

In accordance with a further feature of the invention, in order to obtain the desired reciprocity of the resistors, the non-linear resistors are combined with linear resistors. Suited for this purpose is also the use of non-linear resistors having different properties, or the use of special biasing potentials. If the four-pole devices are to have a desired dependence upon frequency, the nonlinear resistors are to be combined with resistors depending upon corresponding frequencies.

By suitably dimensioning the non-linear resistors it can be accomplished that the four-pole devices act either as amplitude limiting means whereby amplitudes above a definite value will be limited (amplitude low-pass) or that these fourpole devices act as amplitude suppressing means whereby the amplitudes are blocked below a defi nite limit (amplitude-high pass). Principally it is also possible to obtain four-pole devices adapted for a definite amplitudinal range only (amplitude filter band) or which block certain ranges (amplitude blocking band).

The figures 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 embodiment 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 detectors 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 rectifier type. With this arrangement there will be obtained the symmetry of the resistor for positive and negative amplitudes required for the transmission of alternating currents. In both cases the current flow through the two detectors takes place in opposite directions. The curves indicate the corresponding relationship between the resultant resistance R and the voltage U. The potential U is supplied to the rectifier combinations by the direct current source shown in each of Figs. 1 to 4.

When biasing the amplitude-dependent resistors by means of auxiliary potentials the resistance course can be varied at will within wide limits. Figures 3 and 4 show the manner of completing the arrangement according to Figures l and 2 for the purpose of shifting the dependence 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 represented; 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 rectifier devices themselves, it can be accomplished that the resistors according to Figures 1 and 2, or figures 3 and 4 have reciprocal resistance values; in other words, that at the amplitudes to be considered there is:

The example of embodiment of the inventive idea shown in Figure 5 represents a four-pole device in the form of a bridge filter. 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 resistors R1 and R2 having reciprocal resistance values. The terminals E and the terminals A are placed at the end points of the bridge diagonals. If now, the two non-linear resistor combinations R1 and R2 are so dimensioned that they approximately equal each other for amplitudes below a definite limit value, these amplitudes cannot pass through the four-pole device. The higher amplitudes will be subjected to a substantially lower damping since for these amplitudes the bridge 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 rectifier combinations R1 and R2 are equal to each other. Due to this fact, the damping between the input E and the output A is very high. Outside this amplitude scope, the resistances of the rectifier combinations are various, and there is no more balance of the bridge. The damping for this amplitude scope will, therefore, be substantially smaller than for the case previously mentioned.

However the resistors R1 and R2 may also be chosen in such manner that they are equal at large amplitudes while differing greatly at small ampitudes. This results in an amplitude filter in which all amplitudes above a desired limit 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 inductances 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 necessary that the apparent resistance Z of these resistors fulfills the equation A further feature of the idea of the invention resides in that for instance the auxiliary potentials indicated in Figures 3 and 4 are not fixed but can be controlled. In transmission systems having two directions of transmission, such as four-wire lines, an amplitude filter inserted in the one direction of transmission may for instance be so controlled by the transmission current passing in the other direction, that it practically blocks all amplitudes thus acting as echoblocking means.

What I claim is:

1. A four-pole network comprising a bridge circuit having input and output terminals, two of the bridge arms including reactances, and the other two arms each including opposed rectifiers, the rectifiers in one arm being in series relation, and those in the other arm being in parallel relation.

2. In an alternating current transmission network, input and output terminals, a pair of reactances 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 connected to a point between the reactances and to the direct connection, and a pair of rectifiers in series and in opposed relation connected across both reactances.

HANS MAYER.

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