DE3326037A1 - CIRCUIT ARRANGEMENT FOR ANALOGUE TRANSMISSION OF VOICE SIGNALS AND COMMUNICATION TAGS - Google Patents

Description

E. Naiwi rt 1

Circuit arrangement for the analog transmission of speech signals and switching technology identification

The invention relates to a circuit arrangement for analog Transmission of voice signals and switching Identifiers, especially between telephone exchanges, with a two-wire-four-wire implementation and with galvanic isolation through an optocoupler.

Such circuit arrangements are used as an interface circuit between higher-level and subordinate telephone Switching systems, for example between a telephone exchange and the main connection line, or as an interface circuit for a remotely powered one Subscriber terminal used. The interface circuit is usually arranged in the subordinate system.

At present, for such an analog signal transmission balanced two-wire transmission systems are used, mostly also being a DC component, either for remote feed or for transmission of switching technology Indicator (e.g. occupancy, release, choice) additional

ZT / Pi-Bk / Gn

Jul 15, 1983 - 3 -

3326Ö37

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Lent to the voice signal is transmitted. The demand of Earth symmetry is generally raised to avoid crosstalk and interference due to asymmetrical longitudinal voltages 2u avoid.

The two-wire transmission enables maximum utilization of the existing line network and is used as far as possible in the telephone area. With more modern ones Telephone switching systems, in particular telephone private branch exchanges, however, frequently use four-wire transmission internally.

Therefore, there is an inevitable requirement for modern systems to be adapted to existing systems, Line systems and apparatus configurations, whereby a Two-wire to four-wire conversion is required.

There are known circuit arrangements for transmission use capacitive or inductive coupling or a combination of both methods for analog signals. However, such arrangements require large, heavy, and therefore expensive components such as large unipolar condensers generators, feed chokes for direct current loop generation and Transformer carrying direct current. There are also circuits with direct signal coupling and electronic ones Loop gift known. The disadvantages are the low Range, the necessary high tensile strength of the Coupling capacitors, high demands on the component tolerance and the very high symmetry demands and relatively large power losses on the transistors.

From DE-OS 2 649 024 and DE-OS 2 844 304 interface circuits are known in which a galvanic

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see separation by means of an optocoupler where a two-wire to four-wire conversion is provided, and where the power is supplied with constant direct current.

In addition, circuits with the above measures, with the exception of keeping the direct current supply constant, are disclosed in US Pat. No. 4,039,766 and in US Pat. No. 4,039,766 DE-AS 2 627 140 described.

The disadvantage of the known circuits with analog SendesignaIeinspeisung by means of optocouplers is that the circuits for direct current transmission are not stable and are imprecise at lower frequencies.

In addition, the semiconductor circuits do not occur switched operating state high power losses on.

It is the object of the invention to provide a circuit arrangement of the type mentioned at the beginning, which enables modern telecommunications systems, e.g. digital private branch exchanges, to be adapted to conventional switching systems.

According to the invention, this object is achieved in that a signal coupling and a direct current loop output by means of pulse duration modulation (PDM). The pulse duration modulation takes place by means of a comparator to which a sawtooth signal is fed and its switching threshold with the modulation signal to be modulated is changed.

The transmission bandwidth of this arrangement ranges from 0 Hz <= direct current) up to about half the pulse frequency. It

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It is therefore possible to transmit both LF signals and switching direct current identification with one and the same circuit arrangement. Another The advantage of this circuit arrangement is the significantly reduced power loss due to the switched operation.

The invention can be designed particularly advantageously that the pulse generator for pulse duration modulation is a self-oscillating circuit arrangement and consists, for example, of a comparator and an integrator * TO stands. Compared to an external zen * central clock supply has the advantage that it works independently of external interference.

According to a further feature of the invention, the pulse-duration-modulated signal is amplitude-regulated. This is done the incoming signal via a differential amplifier a direct current component obtained and provided to the amplitude control, which is a manipulated variable for the Pulse width modulation circuit supplies. As a result of that the regulation derived from a direct current component this circuit arrangement has the advantage that stability is guaranteed over the entire transmission range.

Further details of the invention emerge from the following description of an exemplary embodiment.

From the single figure is the circuit of an active one

line transformer through which direct current flows. For example, the connection of a telephone exchange via a two-wire main connection line to a higher-level telephone exchange

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Location (office) shown.

An incoming signal is switched through directly via a differential amplifier DIF and a subsequent two-wire to four-wire converter 2M-U.

The DC loop delivery in the direction of the office takes place via a transistor T via the a-wire, a bridge rectifier BG, a low-pass filter TP, an impedance R ', a transistor T, the rectifier BG and the b-wire. Thereby the transistor T is through an optocoupler OK controlled.

The DC loop output is also coupled directly to the transmit signal feed via a comparator K2 S, which is carried out by means of pulse duration modulation. The starting point for the pulse duration modulation is a self- oscillating circuit arrangement, consisting of the comparator K1 and an integrator 0P4, which generates a triangular voltage symmetrical to earth at its output and the comparator K2, which switches in the idle state with a duty cycle of 1: 1. This results in direct current moderately a resistance R for the line termination, which is twice as large as the resistor built into the circuit stand R ':

D = D ^ tx t ty tx ... switch-on time tx ty ... switch-off time

If tx = ty then R '= | -

If control is now carried out in the transmission direction, this takes Modulation is a shift in the switching reference voltage of the comparator K2, whereby the pulse duration of the right

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corner voltage for the optocoupler OK is modulated. The clock frequency is determined by components R9, RIO ₇ . RII and C4 determine the amplification of the signal in the sending direction by the amplitude of the sawtooth (indirectly proportional)

The pulse-duration-modulated signal is transmitted via an optoelectronic switch OS and a subsequent low-pass filter TP delivered to the telephone line. The optoelectronic switch OS consists of a V-MOS transistor T, the OK with the to be transmitted via an optocoupler Useful signal is controlled. A current limit circuit serves as a constant current source KS for shortening the switching times of the optocoupler.

The pulse duration modulated via the transistor T. Signal is demodulated by the low-pass filter TP in order to Avoid disturbances on the line. Simultaneously the low-pass filter TP also serves to protect the transistor against surges.

Since the "switched direct current" also determines the amplitude of the transmission signal (directly proportional), it does is not constant due to the different line lengths, a line resistance-dependent gain control must be carried out for the transmission signal. This is achieved by reducing the sawtooth amplitude at the output of 0P4 for smaller currents and thus increasing the gain in the transmission direction.

Since the current through a constant current source Ik, which to Increasing the switching frequency of OK is used, very small is, you can with a given duty cycle and resistance R 'the voltage on the main connection line for

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Use amplitude control. This is done by the differential amplifier 0P1 brought to control logic level just like the incoming signal (with relatively high attenuation due to common mode rejection), integrated via R3 / C3, inverted by 0P2, not by 0P3 inverted and amplified as a switching reference voltage supplied to the comparator K1, the output of which is between the output voltage of 0P2 (positive) and the output voltage of 0P3 switches back and forth. By modulating the amplitude the square wave voltage also modulates the amplitude of the triangle voltage.

By using an FET operational amplifier (4-fold) Leakage currents can be measured via R1 just above the insulation resistance range achieve.

The transmission frequency range extends from direct current to at half the clock frequency of the pulse generator. If the clock frequency is selected to be high (C ^ 100 kHz), the filter can accordingly can be built up small.

Claims (3)

INTERNATIONAL STANDARD ELECTRIC CORPORATION NEW YORK E. Naiuirt 1 Claims η.) Circuit arrangement for the analog transmission of voice signals and switching characteristics, in particular between telecommunication systems, with a two-wire-four-wire implementation (2/4-U) and with galvanic separation by an optocoupler (OK), characterized in that a signal coupling and a direct current loop is given by means of pulse duration modulation (PDM). 2. Circuit arrangement according to claim 1, characterized in that a pulse generator (PG) for pulse duration modulation is a self-oscillating circuit arrangement which consists of a comparator (K1) and an integrator (0P4). 3. Circuit arrangement according to claim 1 or 2, characterized characterized in that the pulse width modulated signal ampli is controlled by hours. ZT / Pi-Bk / Gn 07/14/1983