DE9218994U1 - Circuit arrangement for the supply of digital devices - Google Patents

Description

G2092

Circuit arrangement for supplying digital devices

The invention relates to a circuit arrangement for supplying terminal devices in communication networks according to the preamble of claim 1.

In the digital communications network, e.g. the integrated services digital communications network (ISDN), physical interfaces are provided between the digital exchange and the subscriber connection. These user network interfaces between the digital exchange and a subscriber connection (2-wire interface) on the one hand and a network termination of the digital exchange and a subscriber connection (2- or 4-wire interface) on the other hand also serve to transmit power to the subscriber connections. Two additional wires are provided for this purpose, or the power is transmitted via the wires that are also used to transmit information. In the latter case, phantom circuits are provided for the power supply. (P. Bocker: ISDN, The integrated services digital communications network, Springer-Verlag, 1986, p. 75).

Transformers are used for the phantom circuits, which are relatively uneconomical in terms of space requirements and financial expenditure compared to other electrical components.

The invention was therefore based on the task of replacing the previous interface transformers for supplying the subscriber connections with an electronic solution.

This object is achieved by the invention as set out in the characterizing part of the first claim. Further advantageous embodiments are the subject of the subclaim.

The advantage of the invention is the significant cost savings with appropriate circuit design of the electronic chokes and the level adjustments using standard components compared to the previously used transformers, as well as a considerably smaller space requirement.

The invention can be used for all interfaces with phantom power. It is described in more detail below using circuit arrangements.

It shows the

Fig. 1 the conventional phantom circuit of an interface, the

Fig. 2 a four-wire interface (SQ interface), Fig. 3 a two-wire interface for shorter line lengths between digital exchange and subscriber connection

(UpQ interface) and the
Fig. 4 a two-wire interface for longer lines between digital exchange and subscriber connection (U _K Q interface).

In all figures, identical components bear the same reference numerals.

The conventional phantom circuit, as shown in Fig. 1, uses transformer UQ, through which energy is fed to the source of the interface of the network termination unit NT. The energy is fed to the transformer US of the

The signal is tapped from the interface of the terminal device TE and made available to the subscriber connection (not shown) as a power supply via the points V+ and V-. At the same time, the lines LTG are used to transmit information, whereby in four-wire operation a transmission direction TX and a reception direction RX are assigned to the lines LTG.

The invention now proposes to replace the transformers UQ and US by electronic chokes.

In a four-wire interface according to Fig. 2, electronic chokes ED are connected between the source or sink and each line wire on both the interface side of the network termination unit NT and on the end device TE. Such electronic chokes ED are known, for example, from DE 38 26 765 C2. For signal coupling and signal decoupling during information transmission, capacitors C are provided for each line wire in the interfaces of the network termination unit NT and the end device TE.

In ISDN systems, the interfaces of the terminal equipment TE are informed via the polarity of the power supply whether normal operation or emergency operation is taking place. In this application, the interfaces of the terminal equipment must be equipped with a reverse polarity protection VP. Furthermore, in systems that are connected to one another via overhead lines, for example, an overvoltage protection Ü must be provided at the line output of the corresponding interfaces of the network termination unit NT and the terminal equipment TE as lightning protection.

· I

If the transformation ratio of the transformers UQ,US (Fig. 1) replaced by the electronic chokes ED is not equal to one, level adjustments PA are used for each line pair at the signal input and output points. The level adjustments PA are connected to the sides of the capacitors C facing away from the electronic chokes ED.

Fig. 3 shows the supply of a two-wire interface for shorter line lengths, which allows the simultaneous transmission of information in both directions, e.g. via the time separation or echo compensation method. The electronic chokes ED at the source of the network termination unit NT are connected between the source and the line wires as in the four-wire interface according to Fig. 2. On the side of the interfaces of the terminal devices TE, only one electronic choke ED is required when a terminal device is connected directly. This is possible because the mechanical structure of the terminal devices has distributed capacitances with respect to earth potential or ground that are approximately symmetrical. The asymmetry at this point is therefore negligible.

For two-wire interfaces for longer connecting lines between the digital exchange and a digital communication system, which is also referred to as a local network, as shown in Fig. 4, two electronic chokes ED are used, each of which is connected to the line wires A, B to the exchange. Since the local networks have their own power supply for their bus system, the energy transfer from the exchange is only used for emergency operation. The sink at the entrance to the local network therefore simultaneously represents the source for emergency operation in the event of a local power supply failure, in order to keep a terminal device operational.

Claims (2)

Protection claims 1. Circuit arrangement for the supply of terminal equipment in communication networks, in which the supply source is assigned to the interface of a network termination unit of the switching center and the sink is assigned to the interface of the terminal equipment, characterized in that electronic chokes (ED) are connected between the source of the interface of the network termination unit (NT) and each line and between lines and the sink of the interface of the terminal equipment (TE), that capacitors (C) are present for each line wire in the interface of the network termination unit (NT) and the terminal equipment (TE) for the signal input and output of the information transmission, that level adjustments (PA) and overvoltage protection (Ü) are provided for each line pair and that reverse polarity protection (VP) is provided on the interface side of the terminal device. 2. Circuit arrangement according to claim 1, characterized in that in the case of two-wire interfaces for shorter line lengths at the interface of the terminal device (TE) when a terminal device is connected directly, only one electronic choke (ED) is connected between the sink and the line.