CH662023A5 - CIRCUIT ARRANGEMENT FOR ANALOGUE TRANSMISSION OF VOICE SIGNALS AND MEDIATION-SPECIFIC TAGS. - Google Patents

Description

The invention relates to a circuit arrangement for the analog transmission of voice signals and switching characteristics, in particular between telephone switching systems, with two-wire-four-wire conversion and electrical isolation by an opto-electronic switch containing an optocoupler.

Such circuit arrangements are used as an interface circuit between higher-level and subordinate telephone switching systems, for example between private branch exchanges and main connecting lines, or as an interface circuit for remote-powered subscriber terminals. The interface circuit is usually arranged in the subordinate system.

Currently, earth-symmetrical two-wire transmission systems are used for the analog signal transmission in the above-mentioned area, whereby usually a direct current component, either for remote power supply or for the transmission of technical identification (e.g. occupancy, triggering, dialing), is transmitted parallel to the voice signal.

The demand for earth symmetry is generally raised in order to prevent crosstalk or humming noises due to asymmetrical longitudinal tension.

The two-wire transmission enables maximum utilization of the existing line network and is used practically uniformly at close range.

In modern telephone switching systems, in particular telephone private branch exchanges, there is a desire for internal four-wire transmission.

Therefore, there is an inevitable demand for the adaptation of modern systems to obsolete systems, line systems and apparatus configurations using two-wire to four-wire implementations.

Circuit designs are known which use capacitive or inductive coupling or a combination of both methods for the transmission of analog signals. However, such arrangements require large (heavy) and therefore expensive components, such as Large unipolar capacitors, feed chokes for DC current supply and DC current-carrying transformers.

Circuits with direct signal coupling and electronic looping are also known. Disadvantages are the short range, the necessary high dielectric strength of the coupling capacitors, high demands on the component tolerances due to the very high symmetry requirements, and relatively large power losses on the transistors.

Interface circuits are known from DE-OS 2 649 024 and DE-OS 2 844 304, in which the electrical isolation is carried out by means of optocouplers, and in which a two-wire to four-wire conversion is provided, and the supply is carried out with constant direct current.

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

The disadvantage of the known circuits with analog sensor design feed by means of optocouplers is that the circuits for direct current transmission are not stable or are inaccurate at low frequencies.

In addition, high power losses occur in the semiconductor circuits in the non-switched operating state.

It is an object of the invention to avoid the disadvantages mentioned.

The means for solving this problem are described in claim 1. The transmission width of this arrangement ranges from 0 Hz (= direct current) to about half the pulse frequency. It is therefore possible to transmit both LF signals and switching-technology direct current indicators with one and the same circuit arrangement. Another advantage of this circuit arrangement is the significantly reduced power loss due to the switched operation. Since the regulation is derived from a direct current component, this circuit arrangement has the advantage that stability is guaranteed over the entire transmission range.

The invention can be embodied in a particularly advantageous manner in that the pulse generator for pulse duration modulation is a self-oscillating device and consists, for example, of a comparator and a pulse generator, the comparator comparing the voice signals or the switching technology identification with the switching frequency voltage supplied by the pulse generator, and that the pulse generator contains a self-oscillating square wave generator and an integrator in a manner known per se, the amplitude of the square wave pulses being set by means of the manipulated variables supplied by the amplitude controller and these square wave pulses being converted in the integrator to square wave pulses controlled by amplitude.

This arrangement has the advantage over an external central clock supply that it works independently of external disturbances.

An amplitude-controlled pulse duration modulation is already known from EP 0 011 093. The amplitude control acts in the modulator stage on the signal to be modulated,

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

662 023

which is disadvantageous if you want to control several modulators with a central amplitude control. This known solution is also very complex in terms of the number of components. The main disadvantage is that the useful signal must not be earth-related. If an earth-related useful signal is nevertheless to be processed, a transformer is required. These disadvantages are avoided in the present invention.

According to a further feature of the invention, the optoelectronic switch contains a V-MOS transistor, which is controlled via an optocoupler with the useful signal to be transmitted, and a current limiter circuit as a constant current source. The optocoupler is a galvanic isolation that can be produced with little effort and the constant current source leads to a shortening of the switching times.

Further details of the invention result from the following description of an exemplary embodiment according to the drawing.

The figure shows the circuit of an active direct current-carrying line transformer. For example, the connection of a private branch exchange via a two-wire main connecting line a, b to a higher-level telephone exchange (Vst) is shown here.

An incoming signal is directly connected through a differential amplifier DIF and a subsequent two-wire-four-wire converter 2/4-U.

The DC current loop in the direction of the office is “switched” via a transistor T, (a wire, bridge rectifier BG, low pass filter TP, impedance R ', transistor T, BG, b wire), which is controlled by an optocoupler OK.

This DC loop gift is also directly coupled (via a comparator K2) to the feed of the transmission signal S or the DC identifier GKZ and is carried out by means of pulse duration modulation. The starting point for the pulse duration modulation is a self-oscillating pulse generator PG, consisting of a further comparator Kl and an integrator OP4, which generates a triangular voltage symmetrical to earth at the output of OP4 and feeds it to the comparator K2, which in the idle state (no GKZ and S signal on Pulse input from K2) switches in the duty cycle 1: 1. At this ratio, since the current flows through the transistor T only during half the time, the average current value would only reach 50% of the maximum value. However, as with the other subscriber stations, a full current average is required. Consequently, the resistance R 'must be half that of an ordinary subscriber (unswitched).

If control is now carried out in the transmission direction, this control performs a shift in the switching reference voltage of comparator K2, as a result of which the pulse duration of the control signal for the optocoupler OK is modulated. The frequency of the clock signal is determined by the values of the resistors R3, R4, R5 and the capacitor C2, the amplification of the signal in the transmission direction by the amplitude of the sawtooth (directly proportional in-5).

The pulse duration-modulated signal is emitted via an optoelectronic switch OS to the subsequent low-pass filter TP to the telephone line a, b.

The optoelectronic switch OS consists of the V-MOS transistor T already mentioned, which is controlled via the optocoupler OK with the useful signal to be transmitted. A current limiter circuit serves as a constant current source KS to shorten the switching times of the optocoupler.

The pulse-duration modulated Si-i5 signal switched via transistor T is demodulated by the low-pass filter TP in order to keep interference on the line away. At the same time, the low-pass filter TP also serves to protect the transistor from overvoltages.

Since the “switched direct current” also determines the amplitude of the transmitted signal (directly proportional), but this is not constant due to the different cable lengths, a line resistance-dependent gain control must be carried out for the transmitted signal.

This is achieved by reducing the sawtooth amplitude (output OP4) in the case of minor disturbances 25 and thus increasing the gain in the transmission direction.

Since the current IK through the constant current source KS (serves to increase the switching frequency from OK) is very small, given known values of the duty cycle 30 and the impedance R ', the DC voltage on the main connecting line a, b can be used for the amplitude control. This is brought to the control logic level by the differential amplifier OP1 just like the incoming signal (relatively high attenuation due to common-mode rejection), integrated in an Am-35 plug-in controller AR via the integrator R2 / C1, inverted by OP2 or not inverted by OP3 and amplified as switching frequency voltages fed to the comparator Kl, the output of which switches back and forth between the output voltage of OP2 / positive) and the output voltage of OP3. The amplitude of the triangular voltage is also modulated by modulating the amplitude of the square-wave voltage.

By using an FET operational amplifier (4-fold), leakage currents above R1 can be achieved just above the insulation resistance range.

The transmission frequency range extends from direct current to half the clock frequency of the pulse generator.

If the clock frequency is selected to be high (approx. 100 kHz), the filter can be constructed correspondingly small.

v

1 sheet of drawings

Claims (3)

662 023 1. Circuit arrangement for the analog transmission of voice signals (S) and switching characteristics (GKZ), in particular between telephone exchanges, with two-wire-four-wire conversion (2/4-U) and electrical isolation by an opto-electronic switch (OS) containing an optocoupler (OK) ), characterized by a pulse duration modulator (PDM), in which the speech signals (S) and the switching characteristics (GKZ) are modulated, further by a demodulating low-pass filter (TP) and a bridge rectifier (BG), the modulated signals (S) and Identification (GKZ) via the optoelectronic switch (OS) and from its output via the filter (TP) and the rectifier (BG) are fed to a two-wire line (a, b), and through a differential amplifier (DIF), via which one of the other the two-wire line (a, b) incoming signals or / or characteristics derived direct current component is fed to an amplitude controller (AR), d it provides a manipulated variable for the amplitude of the switching frequency voltage of the modulator (PDM). 2. Circuit arrangement according to claim 1, characterized in that the pulse duration modulator (PDM) consists of a comparator (K2) and a pulse generator (G), the comparator (K2) identifying the speech signals (S) and the switching technology identifier ( GKZ) with the switching frequency voltage supplied by the pulse generator, and that the pulse generator (PG) contains a self-oscillating square wave generator (Kl, R3, R4, R5) and an integrator (OP4, C2), the amplitude of the output signal of the square wave generator using that of a Amplitude controller (AR) supplied manipulated variables is set and this square-wave signal is converted in the integrator into a triangular signal with an amplitude proportional to the amplitude of the square-wave signal. 2nd PATENT CLAIMS 3. Switching arrangement according to claim 1 or 2, characterized in that the optoelectric switch (OS) is a V-MOS transistor (T) which is controlled by the optocoupler (OK) with the useful signal to be transmitted, and a current limiter circuit as Contains constant current source (KS) to shorten the switching times of the optocoupler.