INTERFACE CIRCUIT WITH TWO-WIRE FOUR-WIRE CONVERSION FOR TELEPHONE EXCHANGE PLANTS

The invention concerns an interface circuit with two-wire four-wire conversion for telephone exchange plants, with galvanic separation by an opto coupler a contained opto-electronic switch. Such switching configurations are used as interface circuit between superordinate and subordinated telephone exchange plants, for example between PABX installations and Hauptanschlußleitungen, or as interface circuits of fed participant mechanisms. The interface circuit is usually in the subordinated plant arranged. At present earthsymmetrical two-wire transmission systems use find for the analog signal transmission within the above-mentioned range, whereby mostly also a direct current component, either to the remote supply or parallel to the transmission of switching-oriented characteristics (e.g. proofs, will transfer releasing, choice), to the Sprachsignal. The demand for earth symmetry is generally raised, in order to rear-stop crosstalk and/or humming noises by asymmetrical direct-axis component of voltage. The two-wire transmission makes a maximum utilization possible of the existing power mains and practically uniformly at close range is used. With more modern telephone exchange plants, in particular the demand exists PABX installations for internal four-wire transmission. Therefore inevitably the demand results after the adjustment of modern resting against veraltetete plants, line systems and apparatus configurations by means of two-wire four-wire conversion. There is circuit conceptions well-known, which use capacitive or inductive coupling or a combination of both methods for the transmission of similar signals. Such arrangements need however large (heavy) and from there expensive elements, like e.g. large unipolar condensers, Speisedrosseln for the direct current loop gift and gleichstromdurchflossene transducers. There is also circuits with direct signal linking and electronic loop gift well-known. Thereby the small range, the necessary high tension strain of the Koppelkondensatoren, high requirements is unfavorable to the element tolerances because of the very high demands for symmetry, as well as relatively large energy dissipations at the transistors. From the DE-OS 2649024 and the DE-OS 2844304 is interface circuits well-known, with which the galvanic separation takes place by means of opto couplers, and with which a two-wire four-wire conversion are intended, and which take place supply with constant direct current. Further are circuits with that managing stated measures, with exception of the automatic constant of the food direct current, in which US-PS Nr.4, 039.766 geoffenbart and in the DE-AS 2627140. The disadvantage of the well-known circuits with similar transmission signal injection by means of opto couplers is in that the circuits for GIeichstromübertragung not stably and/or with low frequencies are inaccurate. In addition high energy dissipations arise with the monoliths in the not-switched operating condition. Task of the invention the disadvantages mentioned are to be avoided. In accordance with the invention this task is solved thereby that the Sprachsignale and the switching-oriented characteristics in a Pulsdauermodu! ator to be modulated, these modulated signals over the opto-electronic switch and at its exit over a demodulating low-pass filter and a bridge rectifier of the two-wire line are supplied and that a direct current component derived from signals arriving at the two-wire line is supplied an amplitude automatic controller by way of a sum-and-difference amplifier, to which a correcting variable makes available for the amplitude of the switching frequency tension of the pulse continuous modulator. The transmission band width of this arrangement is enough from 0 cycles per second (= direct current) to approximately to the half pulse frequency. It is possible for the same Sohaltungsanordnung to transmit both NF-signals and switching-oriented direct current characteristics also. A further advantage of this switching configuration is the substantially decreased energy dissipation by the switched enterprise. Since the regulation is derived from a direct current component, this switching configuration has still the advantage that stability is ensured over the entire transmission range. The invention can be trained thereby particularly favourably that the pulse continuous modulator consists in actually well-known way of a comparator and a pulse generator, whereby the comparator compares the Sprachsignale and/or the switching-oriented characteristics with the switching reference tension supplied by the pulse generator, and that the pulse generator contains into actually well-known way a swinging square-wave generator and an integrator, whereby the amplitude of the square-wave impulses is stopped by means of the correcting variables supplied by the amplitude automatic controller and these square-wave impulses are converted in the integrator to amplitude-steered triangular pulses. This arrangement has the advantage in relation to an external central clock supply that lo it works independently of external disturbances. A amplitude-regular pulse duration modulation is already well-known from the EP 0011093. The adjusting of amplitude affects thereby in the modulator stage the signal which can be modulated, which from disadvantage is, if one liked to regulate several modulators with a central adjusting of amplitude. This well-known solution is very complex also seen from the number of construction units. The largest disadvantage consists of that the information signal may not be earthreferred. If a earthreferred information signal is to be processed nevertheless, then a transducer is needed. In the invention these disadvantages are avoided. After a further characteristic the opto-electronic switch contains a V-MOS-transistor, which are steered via an opto coupler with the information signal which can be transmitted, as well as a current limit circuit than regulated current source of the invention. The opto coupler is a galvanic separation producible at small expenditure and the regulated current source leads to a shortening of the Schnitzelten. Further details of the invention result from the following description of a remark example. z5 from Fig.1 is evident the circuit of an active gleiehstromdurchflossenen line transducer. For example here the connection of a PABX installation is over a zweidrähtige Hauptanschlußleitung --A, b: to a superordinate telephone exchange plant --Vst-- shown. An arriving signal E becomes by the sum-and-difference amplifier --DIF-- and following two-wire four-wire converter 2/4-U durchgesehaltet directly. The direct current loop gift toward office is made “switched” by the transistor --T--, (A-vein, bridge rectifier --BG--, Low-pass filters --TP--, Impedance --R', transistor --T--, Bridge rectifiers --BG--, baths), that by an opto coupler --OK ONE -- one heads for. The direct current loop gift is further directly coupled (over comparator --K2--) with the transmission signal injection --S-- and/or direct current characteristics --GKZ--, and by means of pulse duration modulation one makes. Starting point for the pulse continuous modulator --PDM-- is a swinging pulse generator --PG-- consisting of the comparator --Kl-- and the integrator --OP4--, which at the exit of the integrator --OP4-- a delta voltage symmetrical against earth produces, those for the comparator --K2-- one supplies, which in a state of rest in the palpation relationship 1:1 scolded. Thus direct current-moderately a resistance results --R-- for the Leitungsabschluß, which is twice as large like the resistance built in the circuit --R'. tx + ty R = R' tx whereby tx = switch-on time ty = fall time. If tx = ty R R = -- 2 one controls now in transmission direction, then this rejection takes a shift of the switching reference tension of comparator --K2-- forwards, whereby the pulse duration of the square wave voltage for the opto coupler --OK ONE -- one modulates. The clock frequency becomes by the values of the resistances --R3, R4, R5--, and the condenser --C2-- determined, the reinforcement of the signal in transmission direction by the amplitude of the saw tooth (indirectly proportional). The pulse-continuousmodulated signal becomes by a optoelektronisehen switch --OS-- and a following low-pass --TP-- to the Fernspreehleitung --A, b-- delivered. The opto-electronic switch --OS-- consists of a V-MOS-transistor --T-- over an opto coupler --OK ONE -- with the information signal which can be transmitted one steers. A current limiter circuit serves as regulated current source --KS-- to the shortening of the switching times of the opto coupler. I0 over the transistor --T-- switched pulse-continuousmodulated signal becomes by the low-pass filter --TP-- demodulated, in order to rear-stop disturbances on the line. At the same time that serves low-pass filter --TP-- also to the protection of the transistor --T-- before overvoltages. Since the “switched direct current” is also the amplitude of the Sendesignals certainly (directly proportionally), these however due to the different conduit lengths not constant, a line resistance-dependent gain control for the Sendesignal must be accomplished. One obtains this thereby that one with smaller rivers the saw tooth amplitude (exit of the operation amplifier--OP4--) reduced and thus the reinforcement in transmission direction increases. There the river Ik by the regulated current source --KB-- (serves the switching frequency of the opto coupler for the increase --OK ONE --), can one is very small at intended well-known values of the palpation relationship and impedance R' DC voltage at the Hauptanschlußleitung --A, b-- consult for the adjusting of amplitude. This becomes by the sum-and-difference amplifier --DIF-- exactly the same as arriving the signal brought on tax logik levels (relatively high weakenings because of common mode rejections), in an amplitude automatic controller --ACRE-- over the integrating network --R2/C1-- integrated, by the operation amplifier --OP2-- inverted, and/or by the operation amplifier --OP3-- does not invert and strengthens as switching reference tension the comparator --Kl-- supplied, its exit between the output voltage of the operation amplifier --OP2-- (positively) and the output voltage of the operation amplifier --OP3-- hinund shifts. Also the amplitude of the delta voltage is modulated by modulation of the amplitude of the square wave voltage. By the employment of an FET operation amplifier (4fach) derivative stream leave themselves over the resistances --G 1-- scarcely over the insulation resistance range obtain. The transmission frequency range reaches from direct current to the half clock frequency of the pulse generator. If the clock frequency is highly selected (100 kHz), then the filter can be removed accordingly small.