NL7909148A - LINE POWER SUPPLY CIRCUIT FOR A TELECOMMUNICATIONS CENTER. - Google Patents

Description

3 2011-135

? & resume

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Line power supply circuit for a telecommunication exchange.

The invention relates to a line current supply circuit for use with two-wire / four-wire couplings in the line circuits of a telecommunication exchange.

With the increasing application of numerical switching techniques in switchgear requirement of telephone exchanges, it becomes necessary to consider how the functions performed by the known line circuits with electromagnetic relays can be obtained by means of integrated electronic circuits.

The requirements for the coupling include a) line current supply, b) line 10 termination, c) long-side balance, d) transition from two-wire version to four-wire version and e} protection against and / or separation from adverse line conditions. The latter requirement includes the isolation of high transient voltages and AC mains voltages that can be induced in the subscriber lines from the integrated circuits.

The invention provides a two-wire / four-wire line circuit for language communication purposes with line current supply resistors supplying line current to the two-wire circuit, a line isolation transformer connected on the one hand to the two-wire circuit, and on the other hand to forward and reverse amplifiers of the four-wire circuit, the rear amplifier has a high output impedance to provide an output current instead of an output voltage and the forward amplifier has a high input impedance so that the line current supply resistors are also used as line terminating impedances.

The line isolation transformer is preferably also used as a hybrid transformer that couples the two-wire circuit to the four-wire circuit. Furthermore, the reverse amplifier has a negative resistance characteristic to compensate for the fact that the line current supply resistors have a smaller value than the total line impedance.

The latter property is necessary to circumvent the apparent incompatibility of the values required for the line termination, that of the order of 600 JT. line power for a conventional telephone, which requires supply from a 50 V power supply through two 200 SL resistors.

The invention is explained in more detail below with reference to the drawing, which is a diagram of an exemplary embodiment of a circuit according to the invention.

The line circuit includes a two-wire part A and a four-wire part B.

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The two-wire part comprises two wires + and - which are connected via the subscriber's line to the subscriber's telephone set. The four-wire portion of the line circuit includes a forward path GO and a reverse path RET, and these paths provide input terminals and output terminals for the numerical encoder encoding equipment and decoding equipment. This coding equipment and decoding equipment is not shown since it is not important to the invention. Typically, the encoding and decoding equipment is used for converting speech streams received from the subscriber's line, which are fed to the forward path GO and converted into numerical samples (an analog-to-numerical conversion) and to convert numerical samples in speech currents (a numeric-to-analog conversion) that are fed through the reverse path RET.

The unfavorable subscriber line conditions (such as induced mains AC voltages and high surge voltages) are isolated from the forward and reverse path amplifiers A1 and A2 by the transformer T, which also performs the function of a hybrid circuit. The line circuit further includes the line current supply resistors R1 and R2 which additionally form the line termination impedance.

In practice, a conventional telephone set is designed to operate according to its specifications if it is each supplied via resistors of 200JT from a power source with a voltage of 50 V. In order to obtain an optimal line termination, the line termination impedance Zt must be equal to 600 -Ω-, although this depends on the 25 line length. By increasing the supply voltage to approximately 60 V. and using supply resistors of 300_Ω_ each, the supply current is sufficiently close to the nominal value so that the operation of the telephone is not adversely affected. In order to further improve the line termination, a capacitor C1 can be connected along the 30 dashed lines between the wires of the two-wire part A.

Detection of the condition of the hook contact and other line signals can be obtained by non-illustrated voltage measuring devices connected to the wires of the two-wire part A, or by using current measuring devices (not shown) in series with the resistors R1 and R2 are switched. Typically, optical tipping devices may be connected in series with the resistors R1 and R2 to achieve complete separation between line conditions and the line state signaling equipment.

40 During operation, speech signal currents flowing in the two-wire 7909148 - 3 - * part A are applied to the line terminating impedance Zt and the resulting voltage is applied to the winding W2 and from there to the amplifier A1 via the windings W3 and W4. , where the line ball impedance Zb provides the line adjustment. However, signals at the output 5 of amplifier A2 are divided between the reflected impedance of the line and the line termination as it occurs on the winding W1 and the balance impedance Zb. The signals generated on the winding W1 also occur on the identical winding W2, but in opposite phase with the signal on the balance impedance Zb. These two 10 signals thus cancel each other at the input of amplifier A1.

As mentioned above, the termination impedance Zt also serves to supply the line current. In order to avoid this terminal impedance from being lowered by the amplifiers A1 and A2, it is necessary to choose the input impedance of the amplifier A1 and the output impedance of the amplifier A2 relatively high. The usual way in which a high output impedance for the amplifier A2 is obtained is the use of internal negative feedback circuits of the amplifier to obtain an output current instead of an output voltage. By ensuring that the amplifier A2 has a negative output resistance, the values of the resistors R1 and R2 together can be smaller than the characteristic line impedance, so that it is possible, for example, to supply an existing telephone from a source with a voltage of 50V via line current supply resistors with values of 20011, as usual.

In the above, only an exemplary embodiment has been described.

For example, the transformer T can be replaced by a simple disconnection device, the hybrid function being performed by other conventional hybrid circuits.

7909148

Claims (6)

1. Two-wire / four-wire line circuit for telecommunication purposes, with line current supply resistors supplying line current to the two-wire circuit, a line isolation transformer connected on the one hand to the two-wire circuit and on the other hand connected to the forward and reverse amplifiers of the four-wire circuit circuit, characterized in that the reverse amplifier has a high output impedance and therefore provides an output current instead of an output voltage, and the forward amplifier has a higher input impedance, so that the line current supply resistors are also used as terminating impedance for the line. 2. Cricuit according to claim 1, characterized in that the reverse amplifier has a negative output resistance to compensate for the fact that the line current supply resistors have a value less than the characteristic impedance of the line. Circuit according to claim 1 or 2, characterized in that the isolation transformer is also a hybrid transformer. Cricuit according to one or more of claims 1 to 3, characterized in that line signaling detection equipment is connected to the two-wire part. Circuit according to one or more of Claims 1 to 3, characterized in that line signaling detection equipment is connected in series with the line current supply resistors. 6; Circuit according to claim 5. characterized in that the line signaling detection equipment 25 comprises optical coupling devices. 79 0 9 1 4 8