CA2090379A1 - Communication interface circuit - Google Patents
Communication interface circuitInfo
- Publication number
- CA2090379A1 CA2090379A1 CA002090379A CA2090379A CA2090379A1 CA 2090379 A1 CA2090379 A1 CA 2090379A1 CA 002090379 A CA002090379 A CA 002090379A CA 2090379 A CA2090379 A CA 2090379A CA 2090379 A1 CA2090379 A1 CA 2090379A1
- Authority
- CA
- Canada
- Prior art keywords
- component
- interface circuit
- transistor
- circuit according
- voltage
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/738—Interface circuits for coupling substations to external telephone lines
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Devices For Supply Of Signal Current (AREA)
- Telephonic Communication Services (AREA)
Abstract
Cas 928 RM/sp COMMUNICATION INTERFACE CIRCUIT
ABSTRACT OF THE DISCLOSURE
The invention relates to an interface circuit (5) for use with a communication signal generator and two signal lines (4a, 4b) for the transmission of a communication signal thereon, said communication signal having an AC and a DC component, said interface circuit (5) including a DC
component setting means (7) for setting the relationship between the voltage and the current of said DC component.
The interrface circuit (5) is characterised in that said DC component setting means (7) comprises a current source (9) connectable between said signal lines (4a, 4b) for supplying said DC component with a constant DC current, said current source (9) being responsive to said DC
component voltage such that it is operatable only when said DC component voltage exceeds a predetermined value.
The interface circuit (5) may be used to adapt a telephone apparatus to the communications signal requirements of a particular country.
ABSTRACT OF THE DISCLOSURE
The invention relates to an interface circuit (5) for use with a communication signal generator and two signal lines (4a, 4b) for the transmission of a communication signal thereon, said communication signal having an AC and a DC component, said interface circuit (5) including a DC
component setting means (7) for setting the relationship between the voltage and the current of said DC component.
The interrface circuit (5) is characterised in that said DC component setting means (7) comprises a current source (9) connectable between said signal lines (4a, 4b) for supplying said DC component with a constant DC current, said current source (9) being responsive to said DC
component voltage such that it is operatable only when said DC component voltage exceeds a predetermined value.
The interface circuit (5) may be used to adapt a telephone apparatus to the communications signal requirements of a particular country.
Description
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Case 928 The present invention relates to an inter~ace circuit for use with a communications signal generator and two signal lines for the transmission of a communications signal thereon, said communications signal having an AC
and a DC component and more particularly to interface circuits of this type which includes a DC component setting means for setting the relationship between the voltage and the current of said DC component. The interface circuit of the present invention is particulary adap~ed for use in a telephone system, and will be described in relation to that exemplary use, but it is to be appreciated that the invention is not limited to this particular use.
Conventional telephone systems consist of a number of signal generation/reception stations and associated speakers and microphones, in the form of handsets.
The signal created when a user speaks into a microphone is amplified and combined with a carrier waveform.
This modulated signal is then transmitted to another user via two signal lines. At another station the signal is demodulated and amplified through a speaker in that station for reception by that user.
The modulated signal thus transmitted is requiried b~
the communications standards in each country to meet certain specifications.
For example certain ratios of DC current to voltage between the signal lines that are not permitted. Figure 1 shows an example of a DC current-voltage characteristic, the shaded regions indicating unacceptable values of current/voltage which may not be transmitted over the signal lines. In addition, it is required that the AC
component of the modulated signal and in particular the .
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Case 928 The present invention relates to an inter~ace circuit for use with a communications signal generator and two signal lines for the transmission of a communications signal thereon, said communications signal having an AC
and a DC component and more particularly to interface circuits of this type which includes a DC component setting means for setting the relationship between the voltage and the current of said DC component. The interface circuit of the present invention is particulary adap~ed for use in a telephone system, and will be described in relation to that exemplary use, but it is to be appreciated that the invention is not limited to this particular use.
Conventional telephone systems consist of a number of signal generation/reception stations and associated speakers and microphones, in the form of handsets.
The signal created when a user speaks into a microphone is amplified and combined with a carrier waveform.
This modulated signal is then transmitted to another user via two signal lines. At another station the signal is demodulated and amplified through a speaker in that station for reception by that user.
The modulated signal thus transmitted is requiried b~
the communications standards in each country to meet certain specifications.
For example certain ratios of DC current to voltage between the signal lines that are not permitted. Figure 1 shows an example of a DC current-voltage characteristic, the shaded regions indicating unacceptable values of current/voltage which may not be transmitted over the signal lines. In addition, it is required that the AC
component of the modulated signal and in particular the .
:
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2~9~373 AC-impedance of the signal generation/reception station, as presented to a modulated signal transmitted on the signal lines, meet the communications standards of these specifications.
Conventional telephone systems are designed to meet only one such set of specifications and are thus only capable of use in one country, or in countries with identical specifications. If the telephone system is to be us~d where other specifications exist, the circuitry of the signal generation~reception stations ~ust be analysed, redesigned and modified.
Such redesign is time-consuming, expensive and can only be performed by a person skilled in electronic circuit design. Further the internal electronic circuitry of a telephone signal generation/reception station is not readily accessible to purchasers of telephone systems. In order to modify such internal electronic circuitry, special tools and expertise are required, and such modifications can generally only be performed by skilled tradesman. The expense and inconvenience of such operations has thus meant that prior art telephone systems may not easily be used in countries with differing specifications.
An object o~ the present invention is to overcome or alleviate the above problems in prior art communications systems.
It is a further object of the present invention to provide a system for permittin~ communications systems, such as telephone systems, ~o ~e easily utilised in countries having differing communications si~nal speci~ications.
Another object of the present invention is to provide a system for permitting such utilisation of telephone systems which system may be conveniently, easily and inexpensively effected by purchasers and users of the telephone system.
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The present invention provides an interface circuitcharacterised in that the DC component setting means comprises a current source connectable between said signal lines for supplying said DC component with a constant DC
current, said current source being responsive to said DC
component voltage such that it is operable only when said DC component voltage exceeds a predetermined value.
In one embodiment of the present invention, the interface circuit includes DC component setting means for setting the relationship between the voltage and current of the DC component of the communications signal. A simple circuit may be provided which has no significant effect on other functions of a communications signal generation. The voltage and impedance elements of the circuit may b~s selected to satisfy the relationship between the DC
component voltage and current signal as required by the communications signal specification in the area of operation.
In another embodiment of the present invention, the 2~ interface circuit includes AC component setting means for setting the relationship between the voltage and current of the AC component of the communications signal. Another simple circuit may be provided whose elements may be selected relatively independently from their influence on other parts of the circuit.
The following description refers in more detail to the various features of the communication inter~ace circuit of the present invention. To facilitate an understanding of t~e invention reference is made in the description to the accompanying drawings where the communication interface circuit is illustrated in a prefered embodiment. It is to be understood that the communication interface circuit is not limited to the prefered embodiment as illustrated in the drawings.
2 ~
n the drawings :
Figure 1 is a graph illustrating an example of the DC
current-voltage characteristic re~uired by communications signal specifications.
Figure 2 is a diagrammatic view illustrating an interface circuit according to the present invention.
F.igure 3A is a circuit diagram of a DC component sett.ing means of the interface circuit of figure 2.
Figure 3B is a diagram representing the current~
voltage characteristic of the DC component setting means of figure 3A.
Figure 4 is a diagram representing the circuit diagram of another DC component setting means of the interface circuit of figure 2.
Figure 5A is a circuit diagram of yet another DC
component setting means of the interface circuit of figure 2.
Figure 5B is a current-voltage characteristic of the DC component setting means of figure 5A.
Figure 6 is a circuit diagram of an AC component setting means of the interface circuit of figure 2.
Figure 7 is a circuit diagram of the interface circuit of figure 2.
Figure 2 shows a telephone system 1 including a signal generation/reception station 2, a handset 3 and a communication signal transmission means 4 comprising two signal lines 4a and 4b respectively. Any number of similar stations 2 may be connected to the signal lines ~a and 4b in a like manner. The telephone system 1 further includes an interface circuit 5 connected between the signal generation~reception station 2 and the signal lines 4a and 4b. In this embodiment the interface circuit 5 includes an isolation circuit 6 which provides high isolation resistance and therefore electrical protection for the station 2 from the rest of the telephone system.
2 ~ 9 The interface circuit 5 comprlses DC component setting means 7 and AC component setting means 8 connected between the lines 4a and 4b for controlling respectively the DC component and the ~C component of the signal.
DC component setting means 7 and AC component setting means 8 are connected between signal lines 4a and 4b.
Although both DC component setting means 7 and AC
component settin~ means 8 are shown in Figure 2, it is to be appreciated that both are embodiments only of the characteristic setting means o~ the interface circuit of the present invention. In another embodiment, not shown, ~C component setting means 7 only or AC component setting means 8 only may be included.
The circuit of Figure 3A shows an embodiment of DC
component setting means 7.
The DC component setting means shown in this figure comprises a current source 9 having a voltage regulator circuit 12, a conductor 10, a switching transistor 11 and a biasing resistor 17.
The voltage regulator circuit 12 comprises a biasing resistor 14 and a reverse-biased Zener diode 13.
The biasing resistor 14 is connected between a terminal 15 and the cathode of the Zener diode 13. The collector of the switching transistor 11 is connec~ed to a terminal of the biasing resistor 17. The other biasing resistor 17 is connected with the anode of the Zener diode 13, to the signal line 4b.
The terminal 15 which receives the voltage U as well as the conductor 10 are connected to a positive current source ~rom the circuit of figure 2.
The terminal 15 and the conductor 10 are connected to thq signal line 4a.
The current source 9 is adapted to supply a constant current Ic across the conductor 10 when the switching element 11 is caused to conduct.
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The voltage regulator 12 which, in the embodiment shown, comprises a single voltage regulating element 13 and a biasing resistor 14, controls the operation the switching element llo As shown, voltage regulating element 13, and switching element 11, may comprise respectively a zener diode and switching transistor, but other circuit elements may be used as will be appreciated by those skilled in art. When the voltage between the two signal lines 4a and 4b in Figure 2 is such that the voltage Uref at terminal 16 is greater than the minimum voltage Umin required to switch on switching transistor 11, constant current Ic flows through circuit branch 10. AS the voltage across the base-collector region o~ transistor 11 @ 0,7V, Ic is given by :
Ic = (Uref - 0.7) / Re (where Re = the resistance of the biasing resistor 17) = constant when the voltage at terminal 15 is greater than Umin.
The relationship between the current and voltage of the circuit shown in Figure 3A is given in the current-voltage characteristic of Figure 3s.
When the voltage between the lines 4a and 4b is less than Umin, the voltage at terminal 16 is not sufficient to turn switching transistor 11 on and no current flows in the circuit in circuit branch 10. However when the voltage U exceeds Umin, switching transistor 11 turns on and constant DC current.Ic flows.In the circuit of Figure 3~, the zener diode of voltage regulating element 13, and biasing resistor 14 may ~e appropriately chosen to select the desired voltage Uref at which switching transistor 11 conducts and the resistor 17 may be appropriately chosen to set the value of the constant DC current Ic which flows along circuit branch 10.
Conveniently a circuit exhibiting the voltage-current characteristic shown in Figure 3B may be utilised to meet , ``~ 2 ~ ~ ~ 3 ~ ~3 the communications signal specifications of many countries for the D~ component of a telephone communications signal.
As can be s~en in Figure 3B, such a circuit may be used to avoid the ~orbidden regions on a current-voltage characteristic whilst otherwise providing a constant DC
current.
In addition, due to the short response time of switching transistor 11, a step waveform is provided by the circuit of Figure 3A. The AC resistance of such a step waveform is sufficiently high so as to have no signifiant in~luence on the AC response of the remaining circuitry in a telephone system and may therefore be designed independently from the circuitly affected by the AC
component of a telephone communications signal.
In other that a telephone system including a circuit such as that shown in Figure 3A may be utilized in areas with differing communications signal specifications at least one of resistors 14 and 17 and the voltage regulating element 13 may be replaced. Due to the step response of the characteristic shown in Figure 3B, the changing of components in this circuit has minimal effect on the circuitry affected by the AC component of a telephone communications signal and may easily be effected.
In figure 4 an alternative to the simple replacement of components is provided. DC component setting means 7 is shown connected between ~he signal lines 4a and ~b.
The DC component setting means 7 comprise three zener diodes 22, 23 and 24 connected in series, such that the cathode of one diode is connected to the anode of an adjacent diode, switching transistors 21, 25, 26, 31 and 32, a conductor 10, a biasing resistor RV and biasing resistors 30, 33 and 34.
As in figure 3A, the collector of the switching transistor 21 is connected to the conductor 10. The conductor 10 is connected at its other end to the line 4a.
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The terminals of the biasing 30, 33 and 34 are connected together to the emitter of the switching transistor 21. The other terminal of the biasing resistor is connected to the line 4b, whereas the other terminals of the biasing resistors 33 and 34 axe respectively connected to the collectors of the switching transistors 31 and 32. The emitters of the switching transistors 31 and 32 are each connected to the line 4a.
The bases of the switching transistors 31 and 32 are respectively connected ~o thQ inputs 35 and 36.
The biasing resistor Rv is connected betwe~n the line ~a (terminal lS) and the cathode of the zener diode 22, The anode of the zener diode 24 is connected to the line 4b.
The collector of the switching transistor 25 is connected between the anode of the zener diode 22 and the cathode of the zener diode 23, whereas the emitter of the switching transistor 25 is connected to the collector of the switching transistor 26 between the anode of the zener diode 23 and the cathode of the æener diode 24~
The emitter of the transistor 26 is connected to the line ~b. The bases of the transistors 25 and 26 are connected respectively to the inputs 28 and 29. When the voltage of the DC component of the con~unication signal between terminals 18 and 19 is at a level sufficient for the voltage at terminal 20 to exceed Uref, switching transis~or 21 is turned on. The value of Uref, and subse~uently Umin, can be determined by the selection of either voltage regulating element (zener diode) 22 alone, or in conjunction with either of the voltage regulating elements 23 or 24, or these two elernents combined. The circuit according to this embodiment of the invention also includes transistors 25 and 26 in order to either include or exclude zener diodes 23 and 24 from voltage regulator 27, and may be turned on by the application of a signal to the base of transistors 25 and 26 via terminals 28 and 29.
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. ~--In one embodiment of the invention, this signal is applied by way of a jumper connecting terminals 28 or 29 to the supply voltage of the telephone circuitry. In another embodiment, terminals 28 and 29 may be connected to a data bus and signals may be provided to transistors 25 and 26 by appropriate software. ~s will be well appreciated by the skilled worker in the field, many other means of applying these signals are possible.
When switching transistor 21 is t~lrned on, current flows through resistor 30. Transistors 31 and 32 are additionally provided however so that curren~ may also flow through either or both of resistors 33 and 34.
Transistors 31 and 32 are turned on by the application o~
a si~nal to terminals 35 and 36.
In this way, the minimum voltage Umin between terminals 18 and 19 at which constant current Ic flows in circuit brauch 10 may be adjusted, and the value of the constant current Ic itself may be adjusted, without the need to physically replace circuit components.
Figure 5A shows another embodiment of a DC component setting means of the interface circuit of the present invention. This circuit includes current sources 37 and 38 of the type previously described, connected between signal lines ~a and 4b. One can also use more than two such current sources if necessary.
Voltage regulating elements 39 and 40, and resistors 41, 42, 43 and 44 are chosen so that switching transistor 45 of current source 37 turns on and conducts current I1 at a lower voltage level U1 than does switching transistor 46 of current source 38 at voltage level U2.
Similarly, voltage regulating element 39 and resistor 43 are chosen to provide a level of constant DC current I1, whereas voltage regulating element ~0 and resistor 44 are chosen to provide a level of constant DC current I2 ~hich is added to current I1, when transistor 46 conducts.
In this manner, and as shown by the current voltage ~ .
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characteristic of Figure 5B, a characteristic of multiple steps may be formed which by the appropriate selection of circuit elements can be made to match the com~unications si~nal specifications in a variety of areas of operation.
As shown in Figure 4, current sources 37 and 38 may include suitable adjustment means such as additional voltage regulating elements and resistors so that one telephone system can be used to meet the comm~nications signal specifications in a ~-ariety of areas of operation without the need for the physical rewiring of telephone circuitry.
The circuit of Figure 6 shows an embodiment of the AC
setting means 8 of Figure 2. Figure 6 shows impedance circuit branch 47 connected between signal lines 4.
Impedance circuit branch 47 includes impedance elements 48, g9 and 50 and switching transistor 51.
In the circuit 47, the resistor 48 is connected to the collector of the switching transistor 51, and the other terminal of the capacitor 50 and the resistor 49 are connected together to the emitter of the switching transistor 51.
A terminal of the circuit 47 is connected to the line 4a whilst its other terminal, for which the capacitor 50 and the resistor 49 are connected, is connected to the line 4b.
The AC component setting means B also comprise an input terminal 52 connected by a coupling capacitor 53 to the base of the transistor 51.
A resistor 5A is connected to the base of the transistor 51 and is also connected to a constant DC
current source (not shown).
A communications signal is transmitted to terminal 52, through coupling capacitor 53, to the base of switching transistor 51 and amplifiying the communications signal through circuit branch 47. Circuit branch 5A
supplies a porition of constant DC current Idc from the DC
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setting means 7 (as shown in Fiyure 2) to the base of switching transistor 51 in order to ensure the switching transistor 51 operates in the active region, so that the current of impedance circuit branch 47 remains relatively constant over a wide voltage range between signal lines 4.
As will be appreciated by those skilled in the art, constant DC current Idc may be provided in a number of ways and DC setting means 7 is not required to provide Idc.
As shown in Figure 4, additional impedance elements may be added or excl~lded from impedance circuit branch ~7 using additional switching transistors so that the current-voltage characteristic required in variety of areas of operation may more easily be met.
lS Fi.gure 7 shows a detailed circuit diagram of one embodiment of the interface circuit of the present invention. A signal, representing a spoken message from a microphone for example, is received at input 55 and transmitted to amplifier 56 where the si~nal is amplified.
Although one particular example of an amplifier circui~ is shown, other configurations may equally be employed.
Optoelectronic coupler 57 provides high isolation resistance and electrical prokection for the telephone system. Having passed through optoelectronic coupler 57, the transmitted signal is amplified by AC amplifier 58, transistor 59 conducting when the transmitted signal is present, ac impedance elements 60, 61 and 62 acting to place the signal on signal lines 63 and 64 at a desired voltage. In order that the signal may be fed back to the user, such as through the speaker in a handset, or so that a signal received other than that transmitted by the interface circuit may be heard by a user, ac impedance elements 61 and 62 are appropriately sized so that most current flowing through transistor 59 also flows through ac impedance element 62. This signal is than transmitted 2 ~ ~ ~ 3 ~ ~
across optoelectronic coupler 15 and amplified by amplifier circuit 76 be~ore being received at output 65.
In addition to ac amplifier 58, the signal placed on lines 63 and 6~ is combined with that produced by current sources 66 and 67. Current sources 66 and 67 produce a DC
characteristic such as that shown in Figure 5B. In addition current sources 66 and 67 may contain a number of additional ~oltage regulating elements and for example impedance elements, such as shown in Figure 4, which may be included or excluded in the interface circuit by appropriate signals from a central processing unit elsewhere in the telephone s~stem. Alternatively, an~
additional elements may be selected by jumpers, or other manual control elements, as well be appreciated by those s~illed in the elevant art.
In this particular embodiment of the present invention, additional voltage regulating element 6~ may be included or excluded from current source 67 by controlling switching transistor 69. Jumper connection 70 may be used to connect the base of switching transistor 69, through optoelectronic coupler 71, to either ground or supply voltage Vcc. In this manner, the characteristic of the interface circuit of the present invention may be altered ~or various countries to match the specifications of those countries.
The signal from AC amplifier 58 and current sources 66 and 67 is placed on lines 63 and 64, and transmitted on signal lines 4, having passed through bridge rectifier '72.
Additional circuit elements such as line switch 73 and ring detection circuit 74 are included in the circuit diagram of Figure 7 or completeness but do not form part of the present invention.
While the preferred embodiment of the present invention has been described, it is to be understood that the in~ention is not limited thereto, and may be otherwise embodied within scope of the following claims.
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Conventional telephone systems are designed to meet only one such set of specifications and are thus only capable of use in one country, or in countries with identical specifications. If the telephone system is to be us~d where other specifications exist, the circuitry of the signal generation~reception stations ~ust be analysed, redesigned and modified.
Such redesign is time-consuming, expensive and can only be performed by a person skilled in electronic circuit design. Further the internal electronic circuitry of a telephone signal generation/reception station is not readily accessible to purchasers of telephone systems. In order to modify such internal electronic circuitry, special tools and expertise are required, and such modifications can generally only be performed by skilled tradesman. The expense and inconvenience of such operations has thus meant that prior art telephone systems may not easily be used in countries with differing specifications.
An object o~ the present invention is to overcome or alleviate the above problems in prior art communications systems.
It is a further object of the present invention to provide a system for permittin~ communications systems, such as telephone systems, ~o ~e easily utilised in countries having differing communications si~nal speci~ications.
Another object of the present invention is to provide a system for permitting such utilisation of telephone systems which system may be conveniently, easily and inexpensively effected by purchasers and users of the telephone system.
' ~: -3 7 ~
The present invention provides an interface circuitcharacterised in that the DC component setting means comprises a current source connectable between said signal lines for supplying said DC component with a constant DC
current, said current source being responsive to said DC
component voltage such that it is operable only when said DC component voltage exceeds a predetermined value.
In one embodiment of the present invention, the interface circuit includes DC component setting means for setting the relationship between the voltage and current of the DC component of the communications signal. A simple circuit may be provided which has no significant effect on other functions of a communications signal generation. The voltage and impedance elements of the circuit may b~s selected to satisfy the relationship between the DC
component voltage and current signal as required by the communications signal specification in the area of operation.
In another embodiment of the present invention, the 2~ interface circuit includes AC component setting means for setting the relationship between the voltage and current of the AC component of the communications signal. Another simple circuit may be provided whose elements may be selected relatively independently from their influence on other parts of the circuit.
The following description refers in more detail to the various features of the communication inter~ace circuit of the present invention. To facilitate an understanding of t~e invention reference is made in the description to the accompanying drawings where the communication interface circuit is illustrated in a prefered embodiment. It is to be understood that the communication interface circuit is not limited to the prefered embodiment as illustrated in the drawings.
2 ~
n the drawings :
Figure 1 is a graph illustrating an example of the DC
current-voltage characteristic re~uired by communications signal specifications.
Figure 2 is a diagrammatic view illustrating an interface circuit according to the present invention.
F.igure 3A is a circuit diagram of a DC component sett.ing means of the interface circuit of figure 2.
Figure 3B is a diagram representing the current~
voltage characteristic of the DC component setting means of figure 3A.
Figure 4 is a diagram representing the circuit diagram of another DC component setting means of the interface circuit of figure 2.
Figure 5A is a circuit diagram of yet another DC
component setting means of the interface circuit of figure 2.
Figure 5B is a current-voltage characteristic of the DC component setting means of figure 5A.
Figure 6 is a circuit diagram of an AC component setting means of the interface circuit of figure 2.
Figure 7 is a circuit diagram of the interface circuit of figure 2.
Figure 2 shows a telephone system 1 including a signal generation/reception station 2, a handset 3 and a communication signal transmission means 4 comprising two signal lines 4a and 4b respectively. Any number of similar stations 2 may be connected to the signal lines ~a and 4b in a like manner. The telephone system 1 further includes an interface circuit 5 connected between the signal generation~reception station 2 and the signal lines 4a and 4b. In this embodiment the interface circuit 5 includes an isolation circuit 6 which provides high isolation resistance and therefore electrical protection for the station 2 from the rest of the telephone system.
2 ~ 9 The interface circuit 5 comprlses DC component setting means 7 and AC component setting means 8 connected between the lines 4a and 4b for controlling respectively the DC component and the ~C component of the signal.
DC component setting means 7 and AC component setting means 8 are connected between signal lines 4a and 4b.
Although both DC component setting means 7 and AC
component settin~ means 8 are shown in Figure 2, it is to be appreciated that both are embodiments only of the characteristic setting means o~ the interface circuit of the present invention. In another embodiment, not shown, ~C component setting means 7 only or AC component setting means 8 only may be included.
The circuit of Figure 3A shows an embodiment of DC
component setting means 7.
The DC component setting means shown in this figure comprises a current source 9 having a voltage regulator circuit 12, a conductor 10, a switching transistor 11 and a biasing resistor 17.
The voltage regulator circuit 12 comprises a biasing resistor 14 and a reverse-biased Zener diode 13.
The biasing resistor 14 is connected between a terminal 15 and the cathode of the Zener diode 13. The collector of the switching transistor 11 is connec~ed to a terminal of the biasing resistor 17. The other biasing resistor 17 is connected with the anode of the Zener diode 13, to the signal line 4b.
The terminal 15 which receives the voltage U as well as the conductor 10 are connected to a positive current source ~rom the circuit of figure 2.
The terminal 15 and the conductor 10 are connected to thq signal line 4a.
The current source 9 is adapted to supply a constant current Ic across the conductor 10 when the switching element 11 is caused to conduct.
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The voltage regulator 12 which, in the embodiment shown, comprises a single voltage regulating element 13 and a biasing resistor 14, controls the operation the switching element llo As shown, voltage regulating element 13, and switching element 11, may comprise respectively a zener diode and switching transistor, but other circuit elements may be used as will be appreciated by those skilled in art. When the voltage between the two signal lines 4a and 4b in Figure 2 is such that the voltage Uref at terminal 16 is greater than the minimum voltage Umin required to switch on switching transistor 11, constant current Ic flows through circuit branch 10. AS the voltage across the base-collector region o~ transistor 11 @ 0,7V, Ic is given by :
Ic = (Uref - 0.7) / Re (where Re = the resistance of the biasing resistor 17) = constant when the voltage at terminal 15 is greater than Umin.
The relationship between the current and voltage of the circuit shown in Figure 3A is given in the current-voltage characteristic of Figure 3s.
When the voltage between the lines 4a and 4b is less than Umin, the voltage at terminal 16 is not sufficient to turn switching transistor 11 on and no current flows in the circuit in circuit branch 10. However when the voltage U exceeds Umin, switching transistor 11 turns on and constant DC current.Ic flows.In the circuit of Figure 3~, the zener diode of voltage regulating element 13, and biasing resistor 14 may ~e appropriately chosen to select the desired voltage Uref at which switching transistor 11 conducts and the resistor 17 may be appropriately chosen to set the value of the constant DC current Ic which flows along circuit branch 10.
Conveniently a circuit exhibiting the voltage-current characteristic shown in Figure 3B may be utilised to meet , ``~ 2 ~ ~ ~ 3 ~ ~3 the communications signal specifications of many countries for the D~ component of a telephone communications signal.
As can be s~en in Figure 3B, such a circuit may be used to avoid the ~orbidden regions on a current-voltage characteristic whilst otherwise providing a constant DC
current.
In addition, due to the short response time of switching transistor 11, a step waveform is provided by the circuit of Figure 3A. The AC resistance of such a step waveform is sufficiently high so as to have no signifiant in~luence on the AC response of the remaining circuitry in a telephone system and may therefore be designed independently from the circuitly affected by the AC
component of a telephone communications signal.
In other that a telephone system including a circuit such as that shown in Figure 3A may be utilized in areas with differing communications signal specifications at least one of resistors 14 and 17 and the voltage regulating element 13 may be replaced. Due to the step response of the characteristic shown in Figure 3B, the changing of components in this circuit has minimal effect on the circuitry affected by the AC component of a telephone communications signal and may easily be effected.
In figure 4 an alternative to the simple replacement of components is provided. DC component setting means 7 is shown connected between ~he signal lines 4a and ~b.
The DC component setting means 7 comprise three zener diodes 22, 23 and 24 connected in series, such that the cathode of one diode is connected to the anode of an adjacent diode, switching transistors 21, 25, 26, 31 and 32, a conductor 10, a biasing resistor RV and biasing resistors 30, 33 and 34.
As in figure 3A, the collector of the switching transistor 21 is connected to the conductor 10. The conductor 10 is connected at its other end to the line 4a.
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The terminals of the biasing 30, 33 and 34 are connected together to the emitter of the switching transistor 21. The other terminal of the biasing resistor is connected to the line 4b, whereas the other terminals of the biasing resistors 33 and 34 axe respectively connected to the collectors of the switching transistors 31 and 32. The emitters of the switching transistors 31 and 32 are each connected to the line 4a.
The bases of the switching transistors 31 and 32 are respectively connected ~o thQ inputs 35 and 36.
The biasing resistor Rv is connected betwe~n the line ~a (terminal lS) and the cathode of the zener diode 22, The anode of the zener diode 24 is connected to the line 4b.
The collector of the switching transistor 25 is connected between the anode of the zener diode 22 and the cathode of the zener diode 23, whereas the emitter of the switching transistor 25 is connected to the collector of the switching transistor 26 between the anode of the zener diode 23 and the cathode of the æener diode 24~
The emitter of the transistor 26 is connected to the line ~b. The bases of the transistors 25 and 26 are connected respectively to the inputs 28 and 29. When the voltage of the DC component of the con~unication signal between terminals 18 and 19 is at a level sufficient for the voltage at terminal 20 to exceed Uref, switching transis~or 21 is turned on. The value of Uref, and subse~uently Umin, can be determined by the selection of either voltage regulating element (zener diode) 22 alone, or in conjunction with either of the voltage regulating elements 23 or 24, or these two elernents combined. The circuit according to this embodiment of the invention also includes transistors 25 and 26 in order to either include or exclude zener diodes 23 and 24 from voltage regulator 27, and may be turned on by the application of a signal to the base of transistors 25 and 26 via terminals 28 and 29.
.
: , ~
2 ~
. ~--In one embodiment of the invention, this signal is applied by way of a jumper connecting terminals 28 or 29 to the supply voltage of the telephone circuitry. In another embodiment, terminals 28 and 29 may be connected to a data bus and signals may be provided to transistors 25 and 26 by appropriate software. ~s will be well appreciated by the skilled worker in the field, many other means of applying these signals are possible.
When switching transistor 21 is t~lrned on, current flows through resistor 30. Transistors 31 and 32 are additionally provided however so that curren~ may also flow through either or both of resistors 33 and 34.
Transistors 31 and 32 are turned on by the application o~
a si~nal to terminals 35 and 36.
In this way, the minimum voltage Umin between terminals 18 and 19 at which constant current Ic flows in circuit brauch 10 may be adjusted, and the value of the constant current Ic itself may be adjusted, without the need to physically replace circuit components.
Figure 5A shows another embodiment of a DC component setting means of the interface circuit of the present invention. This circuit includes current sources 37 and 38 of the type previously described, connected between signal lines ~a and 4b. One can also use more than two such current sources if necessary.
Voltage regulating elements 39 and 40, and resistors 41, 42, 43 and 44 are chosen so that switching transistor 45 of current source 37 turns on and conducts current I1 at a lower voltage level U1 than does switching transistor 46 of current source 38 at voltage level U2.
Similarly, voltage regulating element 39 and resistor 43 are chosen to provide a level of constant DC current I1, whereas voltage regulating element ~0 and resistor 44 are chosen to provide a level of constant DC current I2 ~hich is added to current I1, when transistor 46 conducts.
In this manner, and as shown by the current voltage ~ .
:: :
.
3 ~ ~
characteristic of Figure 5B, a characteristic of multiple steps may be formed which by the appropriate selection of circuit elements can be made to match the com~unications si~nal specifications in a variety of areas of operation.
As shown in Figure 4, current sources 37 and 38 may include suitable adjustment means such as additional voltage regulating elements and resistors so that one telephone system can be used to meet the comm~nications signal specifications in a ~-ariety of areas of operation without the need for the physical rewiring of telephone circuitry.
The circuit of Figure 6 shows an embodiment of the AC
setting means 8 of Figure 2. Figure 6 shows impedance circuit branch 47 connected between signal lines 4.
Impedance circuit branch 47 includes impedance elements 48, g9 and 50 and switching transistor 51.
In the circuit 47, the resistor 48 is connected to the collector of the switching transistor 51, and the other terminal of the capacitor 50 and the resistor 49 are connected together to the emitter of the switching transistor 51.
A terminal of the circuit 47 is connected to the line 4a whilst its other terminal, for which the capacitor 50 and the resistor 49 are connected, is connected to the line 4b.
The AC component setting means B also comprise an input terminal 52 connected by a coupling capacitor 53 to the base of the transistor 51.
A resistor 5A is connected to the base of the transistor 51 and is also connected to a constant DC
current source (not shown).
A communications signal is transmitted to terminal 52, through coupling capacitor 53, to the base of switching transistor 51 and amplifiying the communications signal through circuit branch 47. Circuit branch 5A
supplies a porition of constant DC current Idc from the DC
' ' ' ' ' ` "
, ~ 2~9~37~
setting means 7 (as shown in Fiyure 2) to the base of switching transistor 51 in order to ensure the switching transistor 51 operates in the active region, so that the current of impedance circuit branch 47 remains relatively constant over a wide voltage range between signal lines 4.
As will be appreciated by those skilled in the art, constant DC current Idc may be provided in a number of ways and DC setting means 7 is not required to provide Idc.
As shown in Figure 4, additional impedance elements may be added or excl~lded from impedance circuit branch ~7 using additional switching transistors so that the current-voltage characteristic required in variety of areas of operation may more easily be met.
lS Fi.gure 7 shows a detailed circuit diagram of one embodiment of the interface circuit of the present invention. A signal, representing a spoken message from a microphone for example, is received at input 55 and transmitted to amplifier 56 where the si~nal is amplified.
Although one particular example of an amplifier circui~ is shown, other configurations may equally be employed.
Optoelectronic coupler 57 provides high isolation resistance and electrical prokection for the telephone system. Having passed through optoelectronic coupler 57, the transmitted signal is amplified by AC amplifier 58, transistor 59 conducting when the transmitted signal is present, ac impedance elements 60, 61 and 62 acting to place the signal on signal lines 63 and 64 at a desired voltage. In order that the signal may be fed back to the user, such as through the speaker in a handset, or so that a signal received other than that transmitted by the interface circuit may be heard by a user, ac impedance elements 61 and 62 are appropriately sized so that most current flowing through transistor 59 also flows through ac impedance element 62. This signal is than transmitted 2 ~ ~ ~ 3 ~ ~
across optoelectronic coupler 15 and amplified by amplifier circuit 76 be~ore being received at output 65.
In addition to ac amplifier 58, the signal placed on lines 63 and 6~ is combined with that produced by current sources 66 and 67. Current sources 66 and 67 produce a DC
characteristic such as that shown in Figure 5B. In addition current sources 66 and 67 may contain a number of additional ~oltage regulating elements and for example impedance elements, such as shown in Figure 4, which may be included or excluded in the interface circuit by appropriate signals from a central processing unit elsewhere in the telephone s~stem. Alternatively, an~
additional elements may be selected by jumpers, or other manual control elements, as well be appreciated by those s~illed in the elevant art.
In this particular embodiment of the present invention, additional voltage regulating element 6~ may be included or excluded from current source 67 by controlling switching transistor 69. Jumper connection 70 may be used to connect the base of switching transistor 69, through optoelectronic coupler 71, to either ground or supply voltage Vcc. In this manner, the characteristic of the interface circuit of the present invention may be altered ~or various countries to match the specifications of those countries.
The signal from AC amplifier 58 and current sources 66 and 67 is placed on lines 63 and 64, and transmitted on signal lines 4, having passed through bridge rectifier '72.
Additional circuit elements such as line switch 73 and ring detection circuit 74 are included in the circuit diagram of Figure 7 or completeness but do not form part of the present invention.
While the preferred embodiment of the present invention has been described, it is to be understood that the in~ention is not limited thereto, and may be otherwise embodied within scope of the following claims.
.
- ., ' -- . , ,. : ........ . . `. , .` :
.. . ` , ~ . .
.
Claims (26)
1. An interface circuit for use with a communication signal generator and two signal lines for the transmission of a communication signal thereon, said communication signal having an AC and a DC component, said interface circuit including a DC component setting means for setting the relationship between the voltage and the current of said DC component, characterised in that said DC component setting means comprises a current source connectable between said signal lines for supplying said DC component with a constant DC
current, said current source being responsive to said DC component voltage such that it is operatable only when said DC component voltage exceeds a predetermined value.
current, said current source being responsive to said DC component voltage such that it is operatable only when said DC component voltage exceeds a predetermined value.
2. An interface circuit according to claim 1 characterised in that said current source comprises z circuit branch connected between said signal lines, said circuit branch including at least one first impedance element and a first switching element, and a voltage regulator connected between said signal lines for supplying a constant reference voltage (Vref) to said first switching element is caused to conduct and enable said constant DC current (Ic) to flow in said circuit branch.
3. An interface circuit according to claim 2 characterized in that said first switching element comprises a transistor said first impedance element being connected between the emitter of said transistor and one of said signal lines, said voltage regulator comprising a second impedance element connected between said other signal line and the base of said transistor, and a first zener diode connected so as to be reverse-biased between the base of said transistor and said one signal line, such that when said DC component voltage exceeds said predetermined value, said first zener diode is caused to supply said constant reference voltage (Vref) to said transistor base.
4. An interface circuit according to claim 2, characterised in that it further comprises means to vary the impedance of said at least one first impedance element.
5. An interface circuit according to claim 3, characterised in that it further comprises means to vary the impedance of said at least one first impedance element.
6. An interface circuit according to claim 1, characterised in that it furthercomprises means to include or exclude at least one additional impedance element in said circuit branch.
7. An interface circuit according to claim 2, characterised in that it furthercomprises means to include or exclude at least one additional impedance element in said circuit branch.
8. An interface circuit according to claim 3, characterised in that it furthercomprises means to include or exclude at least one additional impedance element in said circuit branch.
9. An interface circuit according to claim 4, characterised in that it further comprises means to include or exclude at least one additional impedance element in said circuit branch.
10. An interface circuit according to claim 57 characterised in that it further comprises means to include or exclude at least one additional impedance element in said circuit branch.
11. An interface circuit according to claim 2, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
12. An interface circuit according to claim 3, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
13. An interface circuit according to claim 4, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
14. An interface circuit according to claim 5, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
15. An interface circuit according to claim 6, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
16. An interface circuit according to claim 7, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
17. An interface circuit according to claim 8, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
18. An interface circuit according to claim 9, characterised in that it further comprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
19. An interface circuit according to claim 10, characterised in that it furthercomprises means to vary the constant reference voltage (Vref) supplied by said voltage regulator.
20. An interface circuit according to any one of claims 3 to 19, characterised in that it further comprises means to include or exclude at least one additional reverse-biased zener diode from being connected in series with said first zener diode between the base of said transistor and said one signal line.
21. An interface circuit according to any one of claims 1 to 19, characterised in that it comprises a plurality of said DC component setting means, at least one of which is individually settable so that the supply of said DC component with acomponent of said constant DC current occurs when the DC component voltage exceeds a predetermined value which differs from that of the remaining DC
component setting means.
component setting means.
22. An interface circuit according to any one of claims 3 to 19, characterised in that it further comprises means to include or exclude at least one additional reverse-biased zener diode from being connected in series with said first zener diode between the base of said transistor and said one signal line; and a plurality of said DC component setting means, at least one of which is individually settable so that the supply of said DC component with a component of said constant DC current occurs when the DC component voltage exceeds a predetermined value which differs from that of the remaining DC component setting means.
23. An interface circuit according to any one of claims 1 to 19, characterised in that it further includes an AC component setting means for setting the relationship between the voltage and current of said AC component, characterisedin that said AC component setting means comprises an impedance circuit branch comprising one or more impedance elements and a transistor said communication signal being transmitted by its application to be base of said transistor, said AC component setting means further comprising a constant current source (Idc) for supplying constant DC current to the base of said transistor so as to cause said transistor to operate in its active-region.
24. An interface circuit according to any one of claims 3 to 19, characterised in that it further comprises means to include or exclude at least one additional reverse-biased zener diode from being connected in series with said first zener diode between the base of said transistor and said one signal line; and an AC component setting means for setting the relationship between the voltage and current of said AC component, characterised in that said AC component setting means comprises an impedance circuit branch comprising one or more impedance elements and a transistor said communication signal being transmitted by its application to be base of said transistor, said AC component setting means further comprising a constant current source (IdC) for supplying constant DC current to the base of said transistor so as to cause said transistor to operate in its active-region.
25. An interface circuit according to any one of claims 1 to 19, characterised in that it further comprises a plurality of said DC component setting means, at least one of which is individually settable so that the supply of said DC component with a component of said constant DC current occurs when the DC component voltage exceeds a predetermined value which differs from that of the remaining DC component setting means; and an AC component setting means for setting the relationship between the voltage and current of said AC component, characterised in that said AC component setting means comprises an impedance circuit branch comprising one or more impedance elements and a transistor said communication signal being transmitted by its application to be base of said transistor, said AC component setting means further comprising a constant current source (IdC) for supplying constant DC current to the base of said transistor so as to cause said transistor to operate in its active-region.
26. An interface circuit according to any one of claims 3 to 19, characterised in that it further comprises means to include or exclude at least one additional reverse-biased zener diode from being connected in series with said first zener diode between the base of said transistor and said one signal line;
a plurality of said DC component setting means, at least one of which is individually settable so that the supply of said DC component with a component of said constant DC current occurs when the DC component voltage exceeds a predetermined value which differs from that of the remaining DC component setting means; and an AC component setting means for setting the relationship between the voltage and current of said AC component, characterised in that said AC component setting means comprises an impedance circuit branch comprising one or more impedance elements and a transistor said communication signal being transmitted by its application to be base of said transistor, said AC component setting means further comprising a constant current source (IdC) for supplying constant DC current to the base of said transistor so as to cause said transistor to operate in its active-region.
a plurality of said DC component setting means, at least one of which is individually settable so that the supply of said DC component with a component of said constant DC current occurs when the DC component voltage exceeds a predetermined value which differs from that of the remaining DC component setting means; and an AC component setting means for setting the relationship between the voltage and current of said AC component, characterised in that said AC component setting means comprises an impedance circuit branch comprising one or more impedance elements and a transistor said communication signal being transmitted by its application to be base of said transistor, said AC component setting means further comprising a constant current source (IdC) for supplying constant DC current to the base of said transistor so as to cause said transistor to operate in its active-region.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9203079 | 1992-03-12 | ||
| FR9203079A FR2688606A1 (en) | 1992-03-12 | 1992-03-12 | INTERFACE CIRCUIT FOR COMMUNICATION APPARATUS. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2090379A1 true CA2090379A1 (en) | 1993-09-13 |
Family
ID=9427695
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002090379A Abandoned CA2090379A1 (en) | 1992-03-12 | 1993-02-25 | Communication interface circuit |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0560246A1 (en) |
| JP (1) | JPH0614102A (en) |
| CN (1) | CN1077577A (en) |
| AU (1) | AU3510393A (en) |
| CA (1) | CA2090379A1 (en) |
| FI (1) | FI931088A (en) |
| FR (1) | FR2688606A1 (en) |
| IL (1) | IL105023A0 (en) |
| TW (1) | TW242207B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2287155B (en) * | 1994-02-23 | 1998-08-12 | Motorola Inc | Telecommunications device |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4354060A (en) * | 1979-07-26 | 1982-10-12 | Stromberg-Carlson Corporation | Electronic telephone |
| US4495382A (en) * | 1982-04-23 | 1985-01-22 | Fairchild Camera And Instrument Corporation | Telephone regulator circuitry |
-
1992
- 1992-03-12 FR FR9203079A patent/FR2688606A1/en not_active Withdrawn
-
1993
- 1993-02-17 TW TW082101101A patent/TW242207B/zh active
- 1993-02-25 CA CA002090379A patent/CA2090379A1/en not_active Abandoned
- 1993-03-08 JP JP5046269A patent/JPH0614102A/en active Pending
- 1993-03-08 EP EP93103659A patent/EP0560246A1/en not_active Withdrawn
- 1993-03-11 FI FI931088A patent/FI931088A/en unknown
- 1993-03-11 AU AU35103/93A patent/AU3510393A/en not_active Abandoned
- 1993-03-11 CN CN93102998.8A patent/CN1077577A/en active Pending
- 1993-03-11 IL IL105023A patent/IL105023A0/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FI931088A0 (en) | 1993-03-11 |
| AU3510393A (en) | 1993-09-16 |
| FR2688606A1 (en) | 1993-09-17 |
| EP0560246A1 (en) | 1993-09-15 |
| CN1077577A (en) | 1993-10-20 |
| FI931088A (en) | 1993-09-13 |
| IL105023A0 (en) | 1993-07-08 |
| JPH0614102A (en) | 1994-01-21 |
| TW242207B (en) | 1995-03-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |