AU639956B2 - Power feeding circuit for telephone subset - Google Patents

Abstract

The arrangement according to the invention is intended to permit simple adaptation of a telephone set or terminal to the power supply constraints which are likely to be imposed upon it at its place of installation when it is at least partly remotely supplied by the telephone line to which it is connected and when it comprises an integrated circuit grouping together its essential means. The arrangement comprises an assembly of means (19, 20) whose, unmodifiable, essential features are incorporated into the integrated grouping circuit, the modifiable adaptation elements (13, 15) being situated outside this integrated circuit. <IMAGE>

Description

1 639956

ORIGINAL

COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-1969 COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED "POWER FEEDING CIRCUIT FOR TELEPHONE SUBSET" The following statement is a full description of this invention, including the best method of performing it known to us:- This invention relates to a matching arrangement for an integrated circuit remotely powered by an analog line and incorporated in a telephone subset or station.

At least some of the electrical power supplied to the subsets or stations is usually provided from the telephone switchboard to which they are connected and via the telephone lines connecting them to this switchboard. The latter includes a very reliable power pack connected to the telephone lines via individual equipments.

Each individual equipment is designed to power a given type of subset or station via a given type of line, the respective limits of both having been predetermined in accordance with the service required.

In particular, each equipment can supply instantaneously only a limited quantity of energy to the telephone line to which it is connected, this quantity being fixed in accordance with the conditions, constraints and possibilities provided for the application considered.

Due to the coexistence of successive generations of installations from various origins, today's telephone subsets and stations must be able to match the various installations on a case by case basis, and each time taking into account the various standards required.

2n, This has many drawbacks, in particular for manufacturers who are technologically capable of gathering, on a single integrated circuit, the various devices required to perform the various functions of a subset or station, but are impaired by the need to provide additional components which can be altered on request, and are therefore located external to the integrated circuit, to suit the various standards in force in the various installations.

The present invention therefore proposes a matching arrangement for an integrated circuit incorporated in a telephone subset or station and remotely powered via two wires, referred to as the conversation wires, of an analog telephone line looped at subset or station level via a semiconductor switching component, the integrated circuit containing at least the main basic circuits required to perform the various functions, in particular telephony-related functions. The matching arrangement is fitted with interfaces used to match the telephone telephone suoset or station, with regard to power supply requirements likely to be encountered at the installation site. These interfaces are connected to the said wires via rectifiers supplying a dc power supply and across the switching component in order to regulate the do current supplied to the subset or station circuits located downstream.

Preferably, the interfaces of the said matching arrangement include a current control circuit, sensitive to the power supply voltage applied to the downstream circuit and to a fixed reference voltage internal to the integrated circuit in which the current control circuit is mainly built-in, the latter acting on the base of the transistor of the switching component so as to regulate the control current flowing via this base in association with a resistor, located outside the integrated circuit to allow for its replacement as well as a matching impedance inserted between the transistor of the switching component and the positive supply terminal of the circuits, located downstream in relation to the telephone line.

In order that the invention may be readily carried into effect, embodimnents thereof will now be described in relation to the drawings, in which: Figure 1 represents a simplified skeleton diagram of a telephone subset or station.

Figure 2 represents an example of a standardised power supply pattern for telephone subset or station.

Figure 3 represents the theroetical diagram of the pattern definition, where the line voltage is shown on the X-axis and the current available in the line on the Y-axis.

Figure 4 represents the diagram of a matching arrangement in accordance with the invention.

The matching arrangement in accordance with the invention is designed to be integrated in a telephone subset or station designed to be remotely powered, in total or in part, from a connecting telephone switchboard via an analog telephone line to which this telephone subset or station is connected.

The telephone switchboard, which may for instance be a standard automatic telephone exchange (not shown) to which are connected the subscriber's lines terminating in individual line equipment, each of which provides for bidirectional transmission of analog signals between a remote telephone subset or station and its connecting switchboard, in which the relevant equipment is housed, and for remote power supply of the subset or station from this switchboard.

To this end, telephone line which comprises at least one pair of wires (Li, L2) for carrying conversation signals, is connected via these two wires to the terminals of a dc current generator (not shown) at line equipment level (not shown), where this line is connected to the connecting switchboard.

Wires Li, L2 of analog telephone line typically terminate on two input terminals of a diode bridge via a protection circuit, in the telephone subset or station they service. Here, the protection circuit, installed upstream of diode bridge is typically symbolised by a current limniting resistor connected in series on wire Li at the telephone subset or station input, and by an over-voltage protection device inserted between the two wires LI, L2.

The voltage applied at the input terminals of diode bridge by the connecting switchboard, via wires LI and L2, provides the dc supply for remote power supply of the telephone subset or station as soon as a continuity loop has been established in this subset or station between these wires.

Here, this looping capability is symbolised by a switch hook contact (CCI) designed to be typically closed when the handset is off-hook and open when the handset is on-hook. This continuity loop may be achieved by other means, for instance by actuation of a switching transistor, referred to as loop switch (not shown since it is standard) which may be controlled via a II ~UI~ special key, referred to as the on-hook dial key, on the relevant telephone subset or station.

The biased and output terminals of diode bridge are connected to the matching arrangement which, in this example, is shown mounted in parallel to contact CCI since it is assumed to contain a loop switch transistor ref. Figure 4.

This matching arrangement ensures dynamic matching oC the telephone subset or station housing it, during the various phases of operation in order to comply with the various requirements prescribed, those being sunmnarised in the loop pattern retained for this type of subset or station with the type of switchboard to which it is connected.

A loop pattern example is shown in Figure 2. It defines the limits for the power consumption of a set during the various phases of operation and is illustrated in the form of a diagram where the power supply voltages are shown on the X-axis, while the power supply currents are shown on the Y-axis. In this pattern example, eight ranges A to H are defined, hatched zones border the authorised zone. The telephone set stability must be guaranteed within the ranges B, C and D, while zones F, G and H are prohibited during continuous operation.

Matching arrangement is itself located upstream of the other circuits and equipments in the telephone subset or station, in relation to the telephone line the protection circuit and the diode bridge It allows for at least some of its electrical power supply, via supply terminals, shown Slhere as A and B.

The other circuits and equipments, viz, items 7A and 7B respectively in Figure i, are mainly those used for the telephony-related operation of the subset or station, and are therefore grouped in this example into one assembly referred to as functional assembly. Some of these circuits and/or equipments are monitored by a management logic

I

The functions carried out by circuits (7A) or equipments which are known per se, are namely an audio function, a duplexer function, a telephone signalling function via line for which these circuits (7A) or equipments are eventually connected to line wires downstream of the protection circuit and in parallel with the input terminals of the diode bridge Connections between line and circuits or equipments (7A, 7B) are not detailed herein, since they are symbolised by two connections connecting assembly to the input terminals of the diode bridge Equipments (7A) of assembly include, for instance, sound transmission and reception transducers of the subset or station and their associated amplifiers and one or more displays.

Circuits (7A) of assembly include, for instance, a 2-wire/4-wire conversion circuit, a decadic or multi-frequency signal generator, etc.

Management logic is generally arranged around at least one microprocessor with which is associated a set of ROM or R4AM memories. At least one data transmission link connects the management logic to the circuits and equipments it monitors in assembly In the preferred example of implementation, the circuits of assembly the management logic and all the components making up the matching arrangement likely to be built in the integrated circuit are incorporated in such a circuit, shown as item 10 on Figure i.

Only the components making up the matching arrangement and associated components making up the subset or station of which they form part, are represented here, and more specifically in Figure 4, since the purpose of the present invention relates only to the matching arrangement.

As shown in Figure 1, the matching arrangement is connected on one side to the output terminals of a diode bridge symbolised in Figures 1 and 4 by the terminal and the earth, and on the other side to supply terminals A and B of management logic and assembly The output terminal is itself connected to terminal via a switching transistor (11) which is the loop switch transistor of the subset or station to Which the matching arrangement belongs.

Transistor here a pnp transistor, is controlled in a known fashion via an npn transistor making up the second stage of a first Darlington pair.

To this end, the collector of transistor (12) is connected to the base of loop switch transistor the emitter of which is connected to the output terminal and the collector of which is connected to the supply terminal via a complex impedance (13) and a Schottky diode (14).

Impedance (13) is the impedance matching the subset or station to the line which, as commonly known, must take into account the flow of low frequency signals and which must be determined in accordance with the characteristics of the line and of the connecting switchboard where this line terminates.

Matching impedance (13) is likely *to vary greatly depending on the lines, switchboards and of course the subset or station in which the matching arrangement is fitted, therefore, it cannot be built into the integrated circuit wher? some of the components making up the matching arrangement are integrated. The same applies to transistors (11 and 12), resistor (15) in series with transistor diode and the two capacitors (16 and 17) as well as diode (18).

Presently, transistor (11) cannot be integrated, if, as is commonly A known, it is likely to switch relatively hI-gh powers and to withstand relatively high voltages.

Transistor (12) which controls the base of loop switch transistor (11) is likely to absorb and therefore dissipate a relatively significant amount of heat, since in this example it is used as a regulator. It is therefore not integrated into the integrated circuit The same applies to resistor (15) inserted between earth and the base of transistor Diode (14) is _I I~ inserted between the complex impedance (13) to which it is connected via its cathode and the supply terminal which is positive, downstream of transistor (11) in relation to the output terminal of the diode bridge. Diode (14) has typically a very low voltage drop in the forward direction and is located between two capacitors (16 and 17), one being inserted between earth and the common point of the cathode of diode the other being inserted between earth and the anode of diode (14).

Capacitor (16) is a filter capacitor, while capacitor (17) is a storage capacitor used to temporarily maintain the power supply at terminals A and B in case of short interruption of supply from transistor for instance in case of open loop dialling. Since both capacitors (16 and 17) are typically of the electrolytic type, they are of course not suited for integration in the integrated circuit The same applies to diode (18) which is a zener diode designed to protect the downstream circuits, le. connected to supply terminals A and B.

Similarly, diode (14) is not integrated in the integrated circuit It is designed to charge the storage capacitor (17) while preventing undesirable charge transfer from the storage capacitor (17) to the filter capacitor (16) in case of power failure.

Conversely, the other components making up the matching arrangement (1) are integrated into the integrated circuit In this example they form a starting circuit (19) at powering up time, when the loop closes, and a current control circuit Starting circuit (19) is designed to enhance a fast rise of the supply voltage VO at the supply terminals A, B, such that this voltage always reaches its normal operating value within a fixed limited time, irrespective of the initial capacitor load. It therefore controls the flow through transistor (11) of a current permitting a fast charge of the relevant capacitors, in particular when the subset or station is powered up.

In this example, starting circuit (19) ncludes a second Darlington pair made up by two npn transistors (21 and 22), the collectors of which are connected in parallel to the base of loop switch transistor (11).

The base of transistor makes up the first stage of this second Darlington pair, and is connected on one side to the collector of npn transistor the emitter of which is earthed, and on the other side to the drain of MOS transistor The source of transistor (24) is earthed and its grid is voltage-controlled via a divider bridge with resistors (25, 26) at the common connection of this grid and at the end terminals where voltage VO is applied and available between supply terminals A and B. The emitters of transistors (22 and 23) are earthed, the first via resistor (27) and the second is directly earthed. The base of transistor (23) is connected to the cmmon point of the emitter of transistor (22) and to resistor In addition, resistor (28) connects the base of transistor (21) to the point common to its collector and to the base of transistor (11).

The value of resistor (27) is used to fix the starting current value, until the voltage at the terminals of the resistor bridge (24, 25) reaches the fixed value VO.

As mentioned above, the matching arrangement in accordance with the pres- 2G ent invention also includes a current control circuit This current control circuit (20) acts on the base of the loop switch transistor (11) via the first Darlington pair comprising transistor (12) and transistor Transistor (12) is located external to the integrated circuit (10) such that the latter does not dissipate too much heat. The npn transistor (29) is integrated into the integrated circuit (10) and typically controls the base of transistor (12) via its own emitter. Typically, the collectors of transistors (12, 29) are connected to the base of the loop switch transistor (11) which they control. The base of transistor (12) is also connected to its emitter via resistor (30) and to its collector via resistor (31) in series with a capacitor (32).

The base of transistor (29) is connected to the collector of transistor (11) via a resistor and may be controlled either by a signal issued from the op-amp or by the loop opening control signal issued from assembly containii 3 the integrated circuit via a control link Op-amp (34) receives the audio signals from the subset on its noninverter input, via link and also connected to the output of a control op-amp (36) via its non-inverter input, via a resistor Op-amp (36) is itself connected via its non-inverter input to the common point of resistors 38, 39 of the divider bridge, at the extremities of which supply voltage VO is applied. The inverter inputs of op-amps (34 and 36) are connected to the fixed reference voltage VR of integrated circuit via resistor (40) and resistor (41) respectively.

Resistor (42) loops the output of op-amp (36) onto its inverter input, this resistor (42) is selected with a value G.R40, G being the gain selected for op-amp (36) and R40 being the resistance value 40. A Schottky diode (43) also connects the point common to resistors (38, 39) to the extremity of resistor (40) connected to reference voltage VR, it is used to limit the voltage difference between the inputs of op-amp (36) when voltage VO rises beyond the preset value.

A reaction loop is generated at op-amp (34) via a resistor (44) in parallel with capacitor (45) between the emitter of transistor (12) and the inverter input of op-amp (34).

For low line currents, the power consumption required by integrated cir- A cuit (10) ie. required mainly by assembly and logic is such that the current flowing through matching impedance (13) remains limited. Voltage VO remains too low for diode (18) to be conducting, and there is practically obtained a circuit corresponding to a current source. Any variation of the current available in the line at the output terminal of diode bridge (4) also occurs at supply terminal A.

I When Vli is the voltage at the output of diode bridge on the and terminals, the following expression is true: Vli Bl B2.Ili where Bl is the voltage at the diode bridge output when the current supplied is null, and B2 is the resistance in series presented by the theoretical generator made up by the matching arrangement, and Ili is the current supplied by the diode bridge.

The term Bl may be considered as being defined bv: B1 Vd C1.VR where Vd is the voltage drop at the terminals of diode (14) and where C1 is defined by the expression: Cl (2G+1)(R38+R39)(Z13+RAB)/R15((R38+R39)+2(G+1)R39.RAB)G being as defined above. R15, R38, R39 being the values of resistors 15, 38, 39. Z13 being the value of impedance (13) and RAB being the value of the load resistance available at supply terminals A, B due to the presence of assembly and management logic The term B2 may be considered as defined by the exprer-:.)n: B2 R15(R38+R39)(Z13+RAB)/(R15(R38+R39)+2(G+1)R39.RAB) Diode (18) sets the maximum value of admissible supply voltage VO from which the matching arrangement operates as a constant current source, any current variation then being taken into account by impedance the following expression can be written: Vli B3 Z13.Ili where B3 Vd (Z13/R15 -l)Vz Vz being the voltage at the terminals of impedance (13).

Consequently, as shown in Figure 3, it is possible to match a telephone subset or station with the requirements defined by a pattern, such as symbolised in Figure 2, by acting at matching impedance level (such as impedance 13) and resistor level (such as resistor 15 of the matching arrangement) without alteration to the components making up the matching arrangement which are integrated into integrated circuit Indeed these components (R15 and Z13) make it possible to act on gradients 1/B2 or 1/Z13 load 11 i m i line for a subset or station powered via an analog telephone line in accordance with the requirements assigned as symbolically shown in Figure 3.

Claims (8)

1. A matching arrangement for an integrated circuit of a telephone subset or station remotely powered via two wires of an analog telephone line which can be looped at the relevant subset or station via a switching transistor, said integrated circuit containing at least circuits required to perform various functions, the matching arrangement being fitted with interface means used to match the telephone subset or station with the power supply requirements likely to be encountered, the said interface means being connected to the telephone line via rectifiers supplying a dc current and across the switching transistor in order to regulate the dc current supplied to the subset or station circuits located downstream of the matching arrangement, wherein the interface means of the said matching arrangement include a current control circuit, responsive to a supply voltage applied to downstream circuits and to a fixed reference voltage internal to the said integrated circuit in which the said current control circuit is mainly integrated, said control circuit acting on the base of the switching transistor so as to regulate the control current flowing via this base in association with a control resistor, located external to the integrated circuit to allow for its replacement, as well as a line matching impedance inserted between the switching tansistor and the positive supply terminal of circuits located downstream of the telephone line.

2. A matching arrangement as claimed in claim 1, including interface means, wherein the control resistor is mounted in series with the base of the switching transistor, to match the telephone subset or station to a low power supply, and wherein the matching impedance matches the subset or station to higher power supplies, and is mounted in series with the emitter-collector junction of the said switching transistor between the latter and supply terminals of downstream circuits, as well as a line voltage limiting diode mounted in parallel with the supply terminals, said diode being external to the integrated circuit together with the control resistor and the matching impedance.

3. A matching arrangement as claimed in claim 2, wherein the current control circuit acts on the current flowing via the base of the switching transistor via a control transistor having its collector-emitter junction in series Sbetween the said base and the control resistor, said control transistor being 14 mounted external to the integrated circuit together with the transistor of the control circuit and the control resistor, in order to reduce the amount of heat dissipated at integrated circuit level.

4. A matching arrangement as claimed in claim 3, wherein the control transistor of the current control circuit is in the form of a Darlington pair, said Darlington pair's first transistor acting on the base of the control transistor via its own emitter, and is built into the integrated circuit.

A matching arrangement as claimed in claim 4, wherein the first transistor in the said Darlington pair of the current control circuit is controlled via at least one fixed-gain op-amp receiving a reference voltage of the integrated circuit on one of its two inputs and, receiving on the other input, a fraction of the supply voltage of said downstream circuits which is supplied via a resistor divider bridge located in the integrated circuit with the op-amp, the first transistor and a diode limiting the maximum voltage between the inputs of the said fixed-gain op-amp.

6. A matching arrangement as claimed in claim 2, including a blocking diode in series with the matching impedance upstream of a storage capacitor in parallel with a line voltage limiting diode, the line voltage limiting diode being upstream of an associated one of the supply terminals, the storage capacitor, the line voltage limiting diode, the separation diode, and the matching impedance being external to the integrated circuit whereby downstream power is maintained during short term loop opening.

7. A matching arrangement as claimed in claim 6, including a starting circuit to ensure that the line voltage at the supply terminals rises to its normal operating value within a time shorter than a fixed limit, irrespective of the initial load of the storage capacitor of the telephone subset or station, said starting circuit being directly powered by the rectifiers and responsive to the line voltage to control the current flowing via the base of the switching transistor. p N~QV~>' UI

8. A matching arrangement substantially as herein described with reference to Figures 1 4 of the accompanying drawings. DATED THIS EIGHTH DAY OF FEBRUARY 1993 ALCATEL N.V. Nv L-