WO1981000658A1 - Affaiblisseur non-reciproque de donnees de lignes telephoniques - Google Patents

Affaiblisseur non-reciproque de donnees de lignes telephoniques Download PDF

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Publication number
WO1981000658A1
WO1981000658A1 PCT/AU1980/000058 AU8000058W WO8100658A1 WO 1981000658 A1 WO1981000658 A1 WO 1981000658A1 AU 8000058 W AU8000058 W AU 8000058W WO 8100658 A1 WO8100658 A1 WO 8100658A1
Authority
WO
WIPO (PCT)
Prior art keywords
line
transformer
isolation device
signals
circuit
Prior art date
Application number
PCT/AU1980/000058
Other languages
English (en)
Inventor
D Whitby
Original Assignee
Electro Med Eng Pty Ltd
D Whitby
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Electro Med Eng Pty Ltd, D Whitby filed Critical Electro Med Eng Pty Ltd
Priority to AU63927/80A priority Critical patent/AU6392780A/en
Publication of WO1981000658A1 publication Critical patent/WO1981000658A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0264—Arrangements for coupling to transmission lines
    • H04L25/0266—Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
    • H04L25/0268—Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling with modulation and subsequent demodulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
    • H04M11/066—Telephone sets adapted for data transmision

Definitions

  • TITLE TELEPHONE LINE DATA ISOLATOR
  • This invention relates to an active isolator for coupling data, audio frequency, or other signals to and from telephone lines or other systems.
  • FIG. 1 A schematic circuit diagram illustrating such an arrangement is shown in Figure 1 of the accompanying drawings.
  • the letter L in Figs. 1 to 4 denotes the connections to a telephone line.
  • Resistor R6 is typically 600 ohms.
  • the transformers have a relatively large laminated iron or ferrite material core, and a large number of turns on primary and secondary windings.
  • the DC line current normally flows through the primary, serving no useful purpose, and necessitates the large core and usually an air gap to prevent core saturation.
  • the resistive isolation (and the high voltage breakdown) can be made high but because of the large mass of the windings in close proximity to each other the capacitive isolation is poor.
  • the isolation of transverse AC voltages AC voltages such as 50 or 60Hz mains voltages impressed across the secondary under fault conditions
  • AC voltages such as 50 or 60Hz mains voltages impressed across the secondary under fault conditions
  • the isolation unit transmitter and protection network
  • the isolation unit will provide a reasonably safe coupling to the telephone line with the following limitations.
  • the bulk and cost of the transformer and network is high.
  • the system only provides coupling of audio signals to and from the telephone line and is basically unsuitable for transferring power from the line, the line power being simply dissipated in the primary winding of the transformer. Any data encoding, decoding, or signal processing circuitry connected to the isolated side of the system must of necessity be powered by external power sources such as mains AC or batteries.
  • opto isolators which are usually solid state devices such as light emitting diodes packaged with light sen'sitive diodes or transistors.
  • Figure 3 of the accompanying drawings A simplified circuit for coupling signals from a line is shown in Figure 3 of the accompanying drawings, and a simplified circuit for coupling signals to and from a line is shown in Figure 4.
  • circuits of Figures 3 and 4 are able to provide high isolation, but still require external power supplies from mains or batteries as they are basically unsuitable for transferring power. In addition, the signal losses across the devices are also quite high.
  • Voltage breakdown devices such as diodes, zener diodes, and gas discharge tubes are sometimes used in conjunction with limiting components such as capacitors or resistors. These systems provide a capability to limit the maximum voltages and currents applied to the line, but - 3 -
  • the degree of isolation is not high and power transfer is generally not possible.
  • An object of the present invention is to provide a telephone line data isolator which will overcome the disadvantages of prior devices. It may also attempt to provide a telephone line data isolator in which the power required for operation of a data input device may be obtained from the line or other system.
  • an isolation device for the bi-directional transfer of desired signals between a first system and a second system, and for preventing the transfer of undesirable signals there ⁇ between, characterized in that said systems are connected either side of a high-frequency transformer (16) .
  • Fig. 5 is a circuit diagram of a first, simple, embodiment of the invention.
  • Fig. 6 is a circuit diagram of a second embodiment of the invention.
  • Fig. 7 is a circuit diagram of a typical active hybrid circuit
  • Fig. 8 is a block diagram of a typical application of the circuit of Fig. 6;
  • Fig. 9 is a circuit diagram of a third embodiment of the invention.
  • FIG. 5 there is shown the primary side 10 of the isolating device, and the secondary side 12 thereof is separated therefrom by an imaginary isolation barrier 14, represented in broken lines.
  • the isolation transformer 16 has been, in prototypes, constructed from two ferrite aerial slabs such as those used in low cost transistor radios. These ferrite slabs were each wound with a single layer of insulated wire and mounted at either side of a 3mm thick highly insulated plastic isolation barrier.
  • the main criteria for the selection of the transformer 16 are -
  • isolation transformers can be as low as 5% of the cost of currently available conventional audio-isolation transformers.
  • the isolation transformer may, of course, be manufactured in other ways, using other materials.
  • RL may consist of (1) a resistor across which signals may be sent to or received from the line or other system,
  • diode bridge DBl is present to ensure that the polarity of the voltage supplied to the primary side of the isolator is always constant regardless of actual line polarity. This is important particularly when the device is connected to telephone lines which do not have a guaranteed or defined polarity.
  • ZDl and Rl form a line surge protection network.
  • the breakdown voltage of ZDl is chosen to be higher than the highest voltage across the primary side of the isolator under all possible line resistance conditions. If under surge or fault conditions the line voltage increases, ZDl will conduct and so limit the voltage applied to the primary side of the isolator to within safe limits for the electronic components used.
  • a passive low pass filter consisting of CHl, Cl and C2 is present to prevent the passage of high frequency currents in the primary side of the isolator from reaching the telephone line or other system to which the isolator is connected.
  • Capacitor C2 provides a low impedance path for correct operation of the high frequency transformer driver (QI and Q2) .
  • the low pass filter has a high series and low parallel impedance for the high frequency currents, and a low series and high parallel impedance for the signals within the bandwidth of the line: audio, data or other signals in the approximate range DC to 30KHz.
  • ZD2 is present to provide, via R2 from the positive line voltage, a regulated supply for the high frequency oscillator.
  • Capacitor C3 is a low impedance bypass for all frequencies present in the isolator.
  • Resistor R2 may be replaced by a constant current source or constant current diode, with a consequent advantage of higher dynamic impedance for the signals transferred to and from the isolator.
  • the high frequency oscillator 18 is an astable - 6 -
  • the multivibrator built around a HEX C.M.O.S. inverter integrated circuit.
  • the function of the oscillator could be accomplished in other ways including the use of discrete or integrated transistor circuits.
  • the optimum frequency for the oscillator taking into account economy, efficiency, and size of filter components and the isolatio transformer, has been established by calculation and experiment to be in the order of 150 KHz.
  • the system will operate over a far greater range of oscillator frequencies, and any other frequency may be chosen to suit particular data bandwidths or applications.
  • the output of the oscillator is coupled to a high frequenc drive circuit via R5 and C5.
  • R5 is present to limit the base current of transistor QI, and capacitor C5 is present to speed up the switching time of transistor Q2.
  • Transistor QI is switched on and off at the frequency of the oscillator and an output square wave form with an amplitude close to the DC voltage between A and B on the primary side of the isolator.
  • This square wave form is connected to the base of transistor Q2 whic drives the primary of high frequency isolation transformer Tl in the emitter follower mode.
  • Transistors Ql, Q2 may b discrete or integrated. Other suitable drive circuit configurations could of course be used.
  • a tuned system may be preferable.
  • the values of LI, at the primary of transformer 16, and L6 are chosen to form a series LC resonant circuit with a frequency of resonance a or near the chosen optimum oscillator frequency.
  • the oscillator frequency is set to a higher or lower operating frequency than the L1/C6 series tuned circuit, or alternatively the oscillator is fixed in frequency and the constants of the tuned circuit are set to tune above or below it.
  • the operation of the tuned circuit is as follows:- the primary side of the isolator is coupled to Ll, which is part of a series resonant tuned circuit, by L2 and by mutual induction between the coils an alternating voltage is set up across L2. This alternating voltage is rectified by D2 and filtered by low pass filter CH2, C7, C8. A DC voltage will thus appear across RL.
  • Ll the primary side of the isolator
  • CH2 low pass filter
  • C7, C8 low pass filter
  • a DC voltage will thus appear across RL.
  • the Q of . the series resonant tuned circuit L1/L6 is also altered by the value of Rl, or to put it another way, is altered by the amount of power drawn from the tuned circuit.
  • a direct or alternating voltage applied across RL will increase or decrease the Q factor of the series resonant circuit depending on whether the polarity boosts the voltage produced across RL by the secondary of the isolation transformer.
  • a series LC resonant circuit has a minimum impedance at its resonant frequency. It is also well known that if the Q factor of a series resonant circuit is reduced, its impedance increases, and that if the Q factor is increased its impedance decreases. It will therefore be seen that if the value of RL is changed or modulated, then the loading effect of the series resonant circuit L1/C6 on the line via the high frequency transformer driver will also change or be modulated. In practice, the difference between the oscillator frequency and the series resonant circuit frequency is set to provide an optimum bias point for best linearity of modulation in keeping with supplying sufficient power for the requirements of RL. Signals from the line produce amplitude modulation - 8 -
  • the isolator described may transfer signals from the line to RL and from RL to the line as well as providing DC power into RL for any requirement that may be necessary within the constraints of the power available.
  • C6 is made much larger in value and transformer 16 is made a tightly coupled, closed or near-closed core high frequency transformer.
  • C6 is included in the untuned system to eliminate effective DC current flow due to any possible imbalance in the mark/space ratio of the drive waveform applied to the transformer 16 primary.
  • An AC sine wave drive, or an accurate 1:1 mark/space square wave drive could be used, in which cases C6 could possibly be omitted.
  • Ll and L2 of transformer 16 can be wound on either side of a double insulated bobbin of any one of a number of proprietary ferrite cores such as potcores, or other cores suitable for high frequency operation.
  • a major advantage of the tuned system described is that the high frequency isolation transformer may be of open construction and thus provide an extremely high degree of isolation.
  • a major advantage of the untuned system is higher efficiency of power transfer from the line or system to RL, and in addition exact setting of the oscillation frequency is not necessary due to the untuned nature of the system.
  • Signals from the line will appear between A and B and thus cause changes or modulation in the voltage level applied to primary of the high frequency transformer driver 16.
  • the primary/secondary ratio of transformer 16 could be altered to produce an increase in efficiency whilst utilizing either single ended or bridge drive. Similarly, the primary could be tapped to allow for a push-pull drive circuit of any suitable configuration.
  • Transistors QI to Q4 may be discrete, but it has been found convenient in practice to utilize an integrated or hybrid quad core switching transistor package such as the DH3725. Alternatively other suitable drive circuits either discrete or integrated may be used.
  • the secondary circuit contains all the previously outlined functions of rectifying and filtering with the addition of another supply output 20 which may be required for any data encoding/decoding circuitry required for particular applications.
  • LED 1 is a proprietary constant current light emitting diode with the function of providing:- (A) A visual indication that the line or system is connected to the isolator;
  • LED 1 could be replaced by a resistor, an audio choke or another form of constant current source such as a constant current diode or active constant current source such as a constant current diode or active constant current source.
  • the constant current LED has been found to be the ideal device for the purpose.
  • the negative rail circuitry could be realized around the same components as the positive rail if more " current was required from it.
  • a hybrid circuit either passive or active, may be connected to the secondary side of the isolator to provide separation between input and output signals.
  • the circuit of Fig. 7 is a typical active hybrid circuit.
  • a major advantage of connecting the hybrid circuit to the secondary side of the isolator described is the effect of line resistance and/or impedance changes on the balance of the hybrid circuit is greatly reduced over the effect of these changes when a hybrid is connected directly to the line side of a system.
  • regulators such as voltage dependent resistors are sometimes used to assist the maintenance of hybrid balance over varying line
  • circuitry to perform functions such as the full duplex data modem of Fig. 8 may be powered from the line via the isolator and signals passed to and from the line either via a suitable hybrid circuit or not, whilst maintaining extremely high isolation to and from the line.
  • 22 and 24 are connections to the hybrid circuit, such as that of Fig. 7.
  • 28 is an FSK oscillator
  • 30 is an FSK decoder.
  • 32 is a common return
  • 34, 36 are, respectively, digital data input and digital data output, from and to digital data terminal 38.
  • a further advantage is that data terminals of unknown or untested/approved safety standards may be connected to the data circuits of the isolator described with the knowledge that the line or system is completely protected from any inherent or accidental faults occurring on these terminals.
  • the present device will provide all the power necessary for the data encoding, decoding or signal processing circuitry from the telephone line whilst maintaining a far greater degree of isolation than the traditional approach with the added advantages of low cost and much lower size and weight.
  • Fig. 9 is the circuit of a device which may be used for the isolation from telephone lines of mains- powered equipment associated with telephone terminals. Such equipment may be used as an intermediate element in a telephone system, such as radio, i.e. transmit/receive equipment used to provide remote terminal capability.
  • Rl and Z01 are utilized for transient voltage protection to prevent excessive line transients damaging the active circuitry of the isolator.
  • Ll, Cl and C2 form a passive low pass filter which allows the passage to and from the line of DC levels and signals within the useable range of the device, but prevents high frequency carrier components from being impressed onto the line.
  • CMOS inverters II and 12 are connected in an astable oscillator 18 configuration to 00658
  • the high frequency transformer driver is of the complimentary collector output type and is realized around high voltage high speed PNP and NPN switching ' transistors Q2 and Q3. Supply current for the transformer driver is sourced via R3 with Ql conducting above a fixed threshold. The presence of the circuit including Ql and R3 enables the power to the high frequency oscillator to be increased with the direct current demand of the driver stage. This enables the idle current of the complete circuit to be reduced to very low levels, via sustaining resistor R2, in the absense of load on the isolator secondary circuit 12. C7 is present to prevent DC flow in the primary of transformer 16.
  • the simplified secondary circuit 12 provides DC power (D3 and filter C8/L1/C9) for the load (RL) and the filter which is similar to that on the primary side and prevents the passage of high frequency carrier to the load whilst passing the required signals in both directions.
  • the transformer 16 is transparent to the normal signals used in telephone equipment, but creates a barrier 14 to other signals, and thus prevents the transference of dangerous signals to the telephone line L.
  • the circuit when the telephone terminal is not in use, draws very little power from line L, insufficient to trigger automatic detection apparatus.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Devices For Supply Of Signal Current (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

Un dispositif tampon, essentiellement pour l'affaiblissement non-reciproque d'elements de terminaux telephoniques et de modules de transmission et/ou de reception de donnees par des lignes telephoniques, tout en permettant le transfert de signaux de donnees telephoniques et/ou codes entre les elements/modules et les lignes, comprend un transformateur de haute frequence (16) jouant le role de barriere-tampon, et un circuit comprenant un oscillateur (18) capable de representer des signaux de lignes sous forme de tensions modulees sur le transformateur pour produire un courant continu sur la charge element/ module, et pour representer les fluctuations de ce courant continu sur la ligne en question. Le reseau de circuit permet aussi d'amener le courant continu a la charge pour alimenter un element ou module.
PCT/AU1980/000058 1979-08-31 1980-09-01 Affaiblisseur non-reciproque de donnees de lignes telephoniques WO1981000658A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU63927/80A AU6392780A (en) 1979-08-31 1980-09-01 Telephone line data isolator

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU285/79 1979-08-31
AUPE028579 1979-08-31

Publications (1)

Publication Number Publication Date
WO1981000658A1 true WO1981000658A1 (fr) 1981-03-05

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PCT/AU1980/000058 WO1981000658A1 (fr) 1979-08-31 1980-09-01 Affaiblisseur non-reciproque de donnees de lignes telephoniques

Country Status (2)

Country Link
EP (1) EP0034610A1 (fr)
WO (1) WO1981000658A1 (fr)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0097314A2 (fr) * 1982-06-21 1984-01-04 Applied Spectrum Technologies, Inc. Circuit d'interface pour ligne téléphonique
US4591662A (en) * 1983-06-30 1986-05-27 Horlogerie Photographique Francaise Telephone set-computer terminal assembly with a single decimal keyboard and a switchable local power supply
EP0489215A1 (fr) * 1990-12-05 1992-06-10 International Business Machines Corporation Dispositif de couplage destiné à être connecté à un interface de transmission de données pour la connexion au réseau téléphonique commuté ayant un circuit d'alimentation local pour permettre l'utilisation d'un poste téléphonique et une station de travail et un interface de transmission contenant un tel dispositif
ES2156085A1 (es) * 1999-08-04 2001-06-01 Luengo Luciano Martinez Protector contra "tensiones transferidas".
WO2004112371A1 (fr) * 2003-05-29 2004-12-23 Tdk Semiconductor Corporation Procede et appareil de signalisation duplex integrale dans un transformateur d'impulsions
US8111761B2 (en) 2003-05-29 2012-02-07 Maxim Integrated Products, Inc. Method and apparatus for transmitting data and power across a transformer
EP2469782A1 (fr) * 2010-12-23 2012-06-27 Murrelektronik GmbH Agencement de commutation pour la transmission de signaux
EP2996246A3 (fr) * 2014-09-15 2016-08-03 Analog Devices Global Procédés et structures permettant de générer des signaux de porteuse marche/arrêt verrouillés pour des isolateurs de signaux
US9660848B2 (en) 2014-09-15 2017-05-23 Analog Devices Global Methods and structures to generate on/off keyed carrier signals for signal isolators
US9998301B2 (en) 2014-11-03 2018-06-12 Analog Devices, Inc. Signal isolator system with protection for common mode transients
US10270630B2 (en) 2014-09-15 2019-04-23 Analog Devices, Inc. Demodulation of on-off-key modulated signals in signal isolator systems
US10536309B2 (en) 2014-09-15 2020-01-14 Analog Devices, Inc. Demodulation of on-off-key modulated signals in signal isolator systems

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4304956C2 (de) * 1993-02-18 1998-09-24 Mayer Textilmaschf Verfahren und Vorrichtung zum Schären von Fäden
DE102009053815B4 (de) * 2009-11-18 2013-07-18 Knorr-Bremse Systeme für Nutzfahrzeuge GmbH Betriebsbremseinrichtung eines Fahrzeugs mit Testlauf für Ventile

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4119806A (en) * 1976-12-17 1978-10-10 Jeumont-Schneider Subscriber's line equipment for a telephone exchange
AU2887677A (en) * 1976-10-04 1979-03-22 Ibm Corp. Interface circuit
US4192975A (en) * 1978-02-06 1980-03-11 U.S. Philips Corporation Supply-arrangement for a line circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2887677A (en) * 1976-10-04 1979-03-22 Ibm Corp. Interface circuit
US4119806A (en) * 1976-12-17 1978-10-10 Jeumont-Schneider Subscriber's line equipment for a telephone exchange
US4192975A (en) * 1978-02-06 1980-03-11 U.S. Philips Corporation Supply-arrangement for a line circuit

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0097314A2 (fr) * 1982-06-21 1984-01-04 Applied Spectrum Technologies, Inc. Circuit d'interface pour ligne téléphonique
EP0097314A3 (en) * 1982-06-21 1986-12-10 Applied Spectrum Technologies, Inc. Telephone line interface circuit
US4591662A (en) * 1983-06-30 1986-05-27 Horlogerie Photographique Francaise Telephone set-computer terminal assembly with a single decimal keyboard and a switchable local power supply
EP0489215A1 (fr) * 1990-12-05 1992-06-10 International Business Machines Corporation Dispositif de couplage destiné à être connecté à un interface de transmission de données pour la connexion au réseau téléphonique commuté ayant un circuit d'alimentation local pour permettre l'utilisation d'un poste téléphonique et une station de travail et un interface de transmission contenant un tel dispositif
US5239580A (en) * 1990-12-05 1993-08-24 International Business Machines Corporation Modem-telephone coupler
ES2156085A1 (es) * 1999-08-04 2001-06-01 Luengo Luciano Martinez Protector contra "tensiones transferidas".
WO2004112371A1 (fr) * 2003-05-29 2004-12-23 Tdk Semiconductor Corporation Procede et appareil de signalisation duplex integrale dans un transformateur d'impulsions
US7158573B2 (en) 2003-05-29 2007-01-02 Tdk Semiconductor Method and apparatus for full duplex signaling across a transformer
US8111761B2 (en) 2003-05-29 2012-02-07 Maxim Integrated Products, Inc. Method and apparatus for transmitting data and power across a transformer
EP2469782A1 (fr) * 2010-12-23 2012-06-27 Murrelektronik GmbH Agencement de commutation pour la transmission de signaux
EP2996246A3 (fr) * 2014-09-15 2016-08-03 Analog Devices Global Procédés et structures permettant de générer des signaux de porteuse marche/arrêt verrouillés pour des isolateurs de signaux
US9660848B2 (en) 2014-09-15 2017-05-23 Analog Devices Global Methods and structures to generate on/off keyed carrier signals for signal isolators
US10270630B2 (en) 2014-09-15 2019-04-23 Analog Devices, Inc. Demodulation of on-off-key modulated signals in signal isolator systems
US10536309B2 (en) 2014-09-15 2020-01-14 Analog Devices, Inc. Demodulation of on-off-key modulated signals in signal isolator systems
US9998301B2 (en) 2014-11-03 2018-06-12 Analog Devices, Inc. Signal isolator system with protection for common mode transients

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Publication number Publication date
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