DE1170012B - Circuit arrangement to compensate for the different attenuation of communication lines of different lengths - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: H 04 w

German class: 21 a2- 34/01

Number: 1170 012

File number: S 80337 VIII a / 21 a2

Filing date: July 10, 1962

Opening day: May 14, 1964

In telecommunications technology, telecommunication signals often have to be over lines of different lengths and thus also different attenuation can be transmitted. This is e.g. B. the case with telephone lines, which vary in length depending on the distance between the subscriber and the telephone exchange. The ones transmitted over the communication line Telecommunication signals are therefore more or less attenuated, so that the volume of the received signals is different from case to case. This is generally undesirable, and several proposals for eliminating this phenomenon have already become known. Be like that for example the electroacoustic transducers for subscriber stations in different sensitivity levels manufactured and used in subscriber stations with long connecting lines more sensitive converters than in subscriber stations with short lines. It is also known in subscriber stations with a microphone and receiving amplifiers perform the amplifier elements controllable, so that the gain can be adapted to the respective line attenuation. The adjustment is here in general made by telecommunications officials. The participant is given the opportunity to determine the degree of reinforcement himself to change, so are additional special, generally complex measures to Prevention of self-excitement is necessary if the amplification is too great.

It is also already a circuit arrangement for telephone subscriber stations with a transistor receiving amplifier known, in which the gain of the receiving amplifier is automatically regulated will. Here the gain is automatically generated by a positive feedback for telephone lines increased with high attenuation and decreased for telephone lines with small attenuation. It's closed For this purpose, a non-linear resistor is arranged in the output circuit of the amplifier, which is controlled by the over the telephone line supplied feed current of the amplifier is controlled and at which the voltage for the feedback loop is removed.

In the known circuit arrangement, the feedback is designed as positive feedback and the feedback circuit is routed via the telecommunication line and the opposite subscriber station or the control center. In order to keep the gain fluctuations due to fluctuations in the operating point of the amplifier elements as low as possible, which are known to be relatively large in the case of a coupled amplifier, a stabilization circuit arrangement is at the same time to compensate for the
different attenuation of different lengths
Communication lines

Addendum to the patent: 1153 425

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich,

Munich 2, Witteisbacherplatz 2

Named as inventor:

Dipl.-Phys. Hermann Ritz, Munich-Solln

of the operating point is provided with the aid of the non-linear resistances already mentioned.

Since the feedback circuit via the telecommunication line and the remote call station or the Central unit, the positive feedback voltage fed back to the amplifier input is from the impedance the telecommunication line and the input resistance of the opposite subscriber station or the Headquarters dependent. The impedance of the telecommunication line is not constant, it is just the same depends on the length of the line, as is the attenuation of the telecommunication line. It is therefore in the Feedback loop a transfer element, the transfer size of which is different from case to case. A circuit arrangement has been proposed by the main patent as an improvement the latter circuit arrangement can be viewed.

The starting point for this proposal was a circuit arrangement for one at the end of a communication line arranged amplifier through which the telecommunication signals transmitted over the telecommunication line be amplified and the communication line or a feed line with significant Resistance of the same length is fed from a remote supply voltage source, with the gain of the amplifier by one controlled by the supply voltage or the supply current Feedback is continuously controllable.

409 589 O6

The proposed solution is that the feedback circuit is designed as a negative feedback circuit and is arranged at the location of the amplifier and at least one determining the degree of negative feedback contains non-linear resistance, dei 5 so connected to the supply terminals of the amplifier is that with a change in resistance caused by increasing supply voltage of the Non-linear resistance also increases the degree of negative feedback.

The non-linear resistor thus connects an output terminal in the event of negative voltage feedback of the amplifier with the control electrode of the amplifier. Since the nonlinear resistance of the Feed current is controlled, this connection works not only in terms of alternating current, but also in terms of direct current. This results in a difficulty in setting the operating point of the amplifier. Of the The control electrode of the amplifier should have a predetermined DC potential for setting the operating point are fed. The non-linear resistance would not only have to be that for the negative voltage feedback have prescribed alternating current resistance, but also one for the amplifier element in question suitable DC resistance. This is usually not the case. In addition, has the non-linear resistance for the operating point setting nor the unpleasant property that its direct current resistance changes with the length of the line.

In the proposed circuit arrangements, these difficulties are overcome in that In addition to the non-linear resistance, an additional direct current path is provided which at least partially for alternating current is blocked, and that also the non-linear resistance by another non-linear resistance is added to a voltage divider independent of the supply current.

The invention provides a simpler solution for setting the operating point of the amplifier.

The inventive solution is characterized in that between the tap of the voltage divider and the control electrode of the input stage is the signal source is arranged.

The signal source, generally the microphone of the subscriber station, usually has one of these small DC resistance that this compared to the input resistance of the amplifier element is negligible. In addition, the current consumption is due to the input resistance of the amplifier element so low that the properties of the Signal source cannot be changed. According to a further embodiment of the invention is parallel to one Resistance of the voltage divider and the signal source switched to a non-linear resistor.

The solution according to the invention has the advantage that with a voltage divider made of ohmic resistors the DC potential for the control electrode is independent of the scheme that circuit elements can be saved and that the control stroke is larger because the non-linear resistance another branch must be connected in parallel to determine the operating point.

The invention is explained in more detail by means of an exemplary embodiment on the basis of a figure.

The figure shows a subscriber circuit in which, in a known manner, a listener //, a replica N and a communication line FL are connected to a fork transmitter GÜ and two terminals K 3 and K 4 are provided for connecting a microphone. A microphone amplifier according to the invention is connected between the microphone M and these terminals. It is designed as a two-stage transistor amplifier with an emitter circuit of a transistor Tl as an input stage and a collector circuit of a transistor 72 as an output stage. The collector electrodes of the two transistors are connected to the output terminal K 3 and the emitter electrodes are connected to the output terminal K 4 of the amplifier via the resistors R 1 and R2, respectively. The resistors R 1 and R 2 are used to set the operating point of the transistors, the second being bridged by a capacitor C 3 to prevent negative current feedback. Between the output terminal K 3 and the control electrode B of the first amplifier element is a nonlinear resistance NW is arranged which is dependent on the magnitude of the supply current and thus of the length of the communication line FL and changes the negative feedback of the amplifier. For this purpose, the characteristic curve of the non-linear resistance must be designed in such a way that the degree of negative feedback also increases as the supply voltage between terminals K 3 and K 4 increases. While in the circuit arrangements proposed in the main patent, the direct potential for the control electrode B is obtained by a voltage divider whose tap is directly connected to the control electrode so that the non-linear resistor forms part of the voltage divider, here the voltage divider consists of resistors that are independent of the supply current R 5 and R 6, and the DC potential tapped between these resistors is fed to the control electrode via the microphone M. This results in the advantages already mentioned compared to the arrangement proposed in the main patent.

Claims (5)

Patent claims: 1.Circuit arrangement for an amplifier arranged at the end of a telecommunications line, by which the telecommunication signals transmitted over the telecommunication line are amplified and over the communication line or a feed line with significant resistance from the of the same length is fed from a remote supply voltage source, with the gain of the amplifier by a feedback controlled by the supply voltage or the supply current is continuously adjustable, and the feedback circuit is designed as a negative feedback circuit and is arranged at the location of the amplifier and determines the degree of negative feedback contains non-linear resistance between an output terminal of the amplifier and the Control electrode of the amplifier is arranged and has such a characteristic that with increasing Supply voltage and the degree of negative feedback increases, the DC potential for the control electrode by a voltage divider connected between the supply terminals of the amplifier is obtained after Patent 1153425, characterized in that between the tap of the voltage plate (R 5 / R 6) and the control electrode (B) of the input stage, the signal source (M) is arranged. 2. Circuit arrangement according to claim 1, characterized in that a non-linear resistor (NW) is connected in parallel with a resistor (R 5) of the voltage divider and the signal source (M). 3. Circuit arrangement according to claim 1 or 2, characterized in that the impedance the signal source (M) to the input resistance of the amplifier in the case of long cables is adapted. 4. Circuit arrangement according to claim 2, characterized in that a selenium rectifier is used as the non-linear resistor (NW). 5. Circuit arrangement according to one of claims 1 to 4, characterized in that as Signal source a microphone is used. Considered publications:
German Patent No. 975 971;
German interpretative document No. 1 060 916. 1 sheet of drawings 409 589/306 5.64 © Bundesdruckerei Berlin