TELECOMMUNICATION TERMINAL

Abstract: Telecommunication terminal with automatic switching from 4-wire to 2-wire operation. The terminal is provided with a voltage sensing circuit (5) sensing the way in which DC voltage is fed to the terminal, and in response thereto controlling switches (8, 11) which switch the terminal to prevailing operation conditions.

Description: TELECOMMUNICATION TERMINAL 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 increa¬ sing need of 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 opera¬ tion has the economical advantage that telecommun cation systems alrea- dy installed, such as private automatic branch exchanges (PABX) can be utilized. In the 2-wire case, where transmitter and receiver communi¬ cate 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 arrange enabling the use of 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 condi- tion of the connected lines. It will thus be possible to meet different OMPI demands in respect of 4-wire and 2-wire communication in one and the same terminal. DESCRIPTION OF FIGURES The ivention will now be described in detail with reference to the accompanying drawing, where Figure 1 illustrates a terminal with a vol- tage sensing circuit and switches, and Figure 2 illustrates an alter¬ native voltage sensing circuit. PREFERRED EMBODIMENT Figure 1 illustrates a telecommunication terminal 1 essentially for di¬ gital communication, and disposed such that it can be used for either 4-wire or 2-wire operation without recourse to manual action. The ter- minal, which has two input transformers 2 and 3, is in the 4-wire case, supplied with DC voltage, with the aid of phantom circuitry. This means that voltage of a given polarity is fed over the wire pair A to the transformer 2, while 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: 1) A 1 = +,A 2 = +,B 1 = -,B 2 = - 2) A 1 = -,A 2 = -,B 1 = +,B 2 = + 3) A 1 = 0,A 2 = 0,B 1 = +,B 2 = - 4) A 1 = 0,A 2 = 0,B 1 = -,B 2 = + Cases 1 and 2 correspond to 4-wire operation, while cases 3 and 4 cor¬ respond to 2-wire operation. The terminal 1 is provided with a voltage sensing circuit 5 adapted such that i senses 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 capaci¬ tor 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 con¬ nected 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: 1) The diodes 13, 14 and 16 are blocked, the output F being given a minus potential via its load, 2) The diodes 13, 14 and 16 are conductive and the output F is given a minus potential, 3) The diode 13 is conductive while diode 14 is blocked. The diode 16 is 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-potent al which is determined by the Zener diode 7, 4) The diode14 is conductive while the diode 13 is blocked. The result will be the same as in case 3. The control voltage obtained on the output F in cases 3 and 4 actua¬ tes the switch 8 such that the terminal transmitter 9, from being connected to the secondary winding on the transformer 2 is switched to the secondary winding on the transformer 3 in parallel with the receiver 10. The switch is of conventional type working with gates. The control voltage on the output F furthermore actuates the switch 11 such that it switches in or out components in the transmitter and receiver of the terminal to change the parameters which are affected by the transition from 4-wire to 2-wire operation. Examples of parameters which differ in the two operational cases are the frequency of the clock frequency oscillator and the frame structure of transmitter and receiver. Figure 2 illustrates another embodiment of the voltage sensing circuit 5, where a logical circuit is utilized. In this case the apparatus has two inputs D and E. These are connected via their voltage stabilizing circuits 17 and 18 to the parallel-connected inputs of an OR gate 21 and an inverting AND gate 22. The outputs from these gates are connec¬ ted to the inputs of an AND gate 23. In accordance with the previously mentioned DC voltage conditions there is obtained, if + represents the binary value 1, and - or 0 represents the binary value 0: B. B. 1) 1 1 0 0 2) 0 0 1 1 3) 0 0 1 0 4) 0 0 0 1 Resulting from this the following cases apply to the two inputs D and D) 0 1 0 E) 0 0 1 For the output G at the OR gate 21: G) For the output H at the inverted AND gate 22: H) For the output F at the AND gate 23: F) OMPI This means that voltage sensing circuit output F has control voltage in cases 3 and 4, corresponding to 2-wire operation according to the conditions mentioned. The control voltage is used in the same way as is accounted for in con- junction with the first embodiment. There are,of course,alternative circuit solutions for implementing the logical function described abo¬ ve, allof which are within the scope of the invention.

Claims: CLAIM Telecommunication terminal including a transmitter and a receiver and with switching between four-wire and two-wire operation based on sen¬ sing the DC voltage condition of connected lines where, in the four- wire case, voltage of one polarity is transferred from a center to the terminal via a first wire pair and voltage of the opposite polarity is transferred via second wire pair, while in the two wire case, DC voltage is " transferred from the center to the terminal via the wires in one wire pair, characterized in that the terminal includes a vol¬ tage sensing circuit (5), the two inputs (D,E) of which are connected to a terminal input (B) across which DC voltage is supplied in the two-wire case, the voltage sensing circuit (5) generating one of two signals on an output (F) in response to whether potential .difference is present across the inputs (D,E) or not, said output CF) being con¬ nected to a first switch (8) arranged in a first condition controlled by a first signal from the output (F) to connect the transmitter (9) and receiver (10) each to its respective input (A,B) of the terminal, and in a second condition controlled by a second signal from the output ( F ) , to connect both transmitter (9) and receiver (10) to the terminal input (B), across which the inputs (D,E) of the voltage sensing the circuit (5) are connected, the output (F) also being connected to a second switch (11) which switches in or out circuits which actuate the clock frequency and signal frame structure of the transmitter (9) and recei¬ ver (10), in response to whether the first or the second condition is present. OMPI

Inventors: ERIKSSON ANDERS ERIK, ERIKSSON, ANDERS, ERIK
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1984
Main classification: H04B3
IPC codes: H04B1, H04B3, H04L5