1984-08-29
1986-07-01
Rubinson, Gene Z.
179 18AF, 179170R, 179 81R, H04M 900
Patent
active
045981728
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a telecommunication terminal with automatic switching between 4-wire and 2-wire operation.
BACKGROUND ART
With the development of digital telephony and with the rapidly increasing need for data distribution between centres and terminals over telecommunication lines, the question of the choice of 4-wire or 2-wire telecommunication has become of immediate interest. 4-wire operation has the technical advantage that communication in different directions takes place in different wire pairs, while 2-wire operation has the economical advantage that telecommunication systems already installed, such as private automatic branch exchanges (PABX) can be utilized. In the 2-wire case, where the transmitter and receiver communicate over the same wire pair there are differences, inter alia for the frame structure, from what is applicable to the 4-wire case.
The final standard for digital telecommunication will probably be 4-wire operation. However, 2-wire operation will be necessary during a long transition period, since practically all terminal cabling is 2-wire at the present time. A great problem during the transition period will be to supply the market with both types of terminal. It will also be expensive to gradually change over from 2-wire terminals to 4-wire terminals. One way of solving this problem is to provide for using the same terminal in both systems of operation.
DISCLOSURE OF INVENTION
The basic concept of the invention is to provide automatic switching in a telecommunication terminal, including transmitter and receiver, between 4-wire and 2-wire operation by sensing the DC voltage condition of the connected lines. It will thus be possible to meet different demands in respect of 4-wire and 2-wire communication in one and the same terminal.
DESCRIPTION OF FIGURES
The invention will now be described in detail with reference to the accompanying drawing, where
FIG. 1 illustrates a terminal with a voltage sensing circuit and switches, and
FIG. 2 illustrates an alternative voltage sensing circuit.
PREFERRED EMBODIMENT
FIG. 1 illustrates a telecommunication terminal 1 essentially for digital communication, and disposed such that it can be used for either 4-wire or 2-wire operation without recourse to manual action. The terminal, which has two input transformers 2 and 3, is in the 4-wire case, supplied with DC voltage, with the aid of circuitry (not shown). This means that a voltage of a given polarity is fed over the wire pair A to the transformer 2, while a voltage of the opposite polarity is fed over the wire pair B to the transformer 3. In the 2-wire case, DC voltage is fed over the wires in the wire pair B.
One of the following 4 conditions is applicable to the DC voltage feed:
Cases 1 and 2 correspond to 4-wire operation, while cases 3 and 4 correspond to 2-wire operation.
The terminal 1 is provided with a voltage sensing circuit 5 adapted such that it senses the incoming DC voltage, and in the 2-wire case sends a control voltage which actuates the switches 8 and 11 for switching the terminal from 4-wire to 2-wire operation.
The voltage sensing circuit 5 has three inputs, one input C connected to the center point on the primary winding of the transformer 2 and the other two inputs D and E connected across the center point capacitor 4 on the primary winding of the transformer 3. Via a diode 16 the input C is connected to the output F, while the inputs D and E are connected in parallel to the resistor 15 via the diodes 13 and 14, the other end of the resistor being connected to the output F.
According to the conditions above the following cases are possible: potential via its load, minus potential, without current as a result of the primary side of the transformer 2 being open, and the diode 17 in the DC voltage adjustment circuit 6 is blocked. The output F is given a plus potential which is determined by the Zener diode 7, will be the same as in case 3.
The control voltage obtained on the output F in cases 3 and 4 actuates the switch 8 such that the termi
REFERENCES:
patent: 4173714 (1979-11-01), Bloch et al.
Rubinson Gene Z.
Telefonaktiebolaget LM Ericsson
Vaas R.
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