WO2002073936A2 - Method and arrangement for limiting a ringing current - Google Patents

Method and arrangement for limiting a ringing current Download PDF

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Publication number
WO2002073936A2
WO2002073936A2 PCT/SE2002/000413 SE0200413W WO02073936A2 WO 2002073936 A2 WO2002073936 A2 WO 2002073936A2 SE 0200413 W SE0200413 W SE 0200413W WO 02073936 A2 WO02073936 A2 WO 02073936A2
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WO
WIPO (PCT)
Prior art keywords
current
ringing
value
maximum value
sensed
Prior art date
Application number
PCT/SE2002/000413
Other languages
French (fr)
Inventor
Anders Emericks
Henrik Hellberg
Original Assignee
Telefonaktiebolaget Lm Ericsson (Publ)
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 Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Publication of WO2002073936A2 publication Critical patent/WO2002073936A2/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M19/00—Current supply arrangements for telephone systems
    • H04M19/02—Current supply arrangements for telephone systems providing ringing current or supervisory tones, e.g. dialling tone or busy tone

Definitions

  • the invention relates generally to subscriber line interface circuits (SLICs) and more specifically to ringing current limitation in SLICs.
  • SLICs subscriber line interface circuits
  • a SLIC with integrated ringing must be able to apply a desired constant ringing voltage to a two-wire transmission line to which a subscriber station is connected.
  • the ringing voltage is applied across the subscriber station resistance, also called ringing load, in series with the transmission line resistance. Depending on the values of the ringing load and the line resistance, the ringing voltage causes a ringing current to flow in the transmission line.
  • the value of the ringing load is expressed as a Ring Equivalent Number (REN) that can vary between 0.1 REN and 5 REN, where 1 REN is about 7 k ⁇ .
  • REN Ring Equivalent Number
  • the output stages of the SLIC To save chip area, it is desired to be able to use the output stages of the SLIC to generate the ringing signal.
  • the necessary currents and voltages are within the operating range of the output stages.
  • the output stages of the SLIC are used to supply current and speech signals to the subscriber station.
  • the SLIC is designed as a voltage amplifier and provides a desired ringing voltage.
  • the ringing current is the ringing voltage divided by the load of the two-wire circuit.
  • the output stages of the SLIC have to output a current of up to 100 mA.
  • the ringing current will increase up to 300 mA. This causes a problem in the SLIC in that the power generated in the output stages can cause damage to them. The same is true in case of a fault condition, e.g. upon an unintentional grounding of one of the wires of the two- wire transmission line.
  • the object of the invention is to provide a method and an arrangement for ringing current limitation in a SLIC to limit the ringing current to a value just above the desired ringing current.
  • the ringing current limitation method and arrangement should also quickly reduce the off-hook current or fault condition current and keep it at the desired level until the ringing signal is turned off.
  • the ringing current is sensed relative to a reference current and reduced if it exceeds the reference current.
  • the reference current is so chosen that there is no risk of damaging the output stages.
  • a ringing current when injected into the SLIC, amplified and outputted to the two-wire circuit, it will be detected whether or not the ringing current exceeds the reference current, and if so, the ringing current will be reduced to a peak value equal to or below the reference current.
  • FIG. 1 is a block diagram of an embodiment of a ringing current limitation arrangement according to the invention in a schematically illustrated SLIC, and Figs. 2a and 2b illustrate waveforms in different nodes in the arrangement in Fig. 1. DESCRIPTION OF THE INVENTION
  • Fig. 1 schematically shows a SLIC 1 connected to wires A and B of a two- wire transmission line to a subscriber station (not shown).
  • a load RL connected to the wires A and B in Fig. 1 represents a sum of the line resistance and the ringing load of the subscriber station.
  • An AC ringing signal intended for the subscriber station is injected into the SLIC 1 via an input terminal IN that is connected to an input terminal of a current amplifier 2.
  • the current amplifier 2 has two output terminals and is adapted to output equal currents II and 12 to respective input terminals of a controllable current attenuator 3.
  • the current attenuator 3 has one control input terminal connected via a node C to an output terminal of a current comparator 4, and two output terminals connected to input terminals of respective current amplifiers 5 and 6.
  • the node C is connected to ground via a capacitor Cl in parallel with a resistor Rl.
  • the control input of the current attenuator 3 is of a high resistance. Thus, the current attenuator 3 is controlled by the voltage in node C.
  • the current amplifiers 5 and 6 are adapted to amplify the ringing currents II ' and 12' by amplification factors +g and -g, respectively, before ringing currents IL and -IL, respectively, are applied to the wires A and B via the output terminals of the respective current amplifier 5 and 6.
  • a voltage controlled current source 8 is connected with its input terminals to the wires A and B, respectively, and with its output terminal to the input terminal of the current amplifier 2.
  • the voltage controlled current source 8 senses the line voltage NL across the load RL and feeds a phase-inverted signal back to the current amplifier 2.
  • a fixed amplification is obtained between the injected ringing signal and the line voltage NL. Consequently, the ringing current IL will increase when the load RL is decreased e.g. when the subscriber station goes off-hook.
  • a value of the ringing current IL is sensed by means of a current sensor 7 that, in the embodiment in Fig. 1, is interconnected between the output terminal of the current amplifier 5 and the wire A to sense an actual value of the ringing current IL.
  • the current sensor 7 is adapted to output a rectified version 14 of the ringing current IL to one input terminal of the current comparator 4. Another input terminal of the current comparator 4 is connected to a reference DC current source IREF that is adapted to output a fixed reference current 15.
  • the reference current 15 represents the maximum allowable peak value of the ringing current IL and is set such that there is no risk for the ringing current to damage the output stages, i.e. the current amplifiers 5 and 6.
  • the reference DC current source IREF has to be scaled down to output the reference current I5/g.
  • the current comparator 4 If the current 14 exceeds the reference current 15, the current comparator 4 outputs a control current 13 to the node C.
  • the current 13 charges the capacitor Cl and the capacitor Cl is discharged towards ground through the resistor Rl.
  • the voltage caused by the current 13 in the node C i.e. on the control input terminal of the current attenuator 3, controls the current attenuator 3 to attenuate the ringing currents II and 12 in proportion to the value of the voltage.
  • the current 13 will be outputted by the current comparator 4 as long as the current 14 exceeds the reference current 15.
  • Fig. 2a is a diagram of the rectified ringing current 14 supplied by the current sensor 7 to the current comparator 4 to be compared with the reference current 15 provided by the ' DC current source IREF.
  • the subscriber station goes off-hook.
  • a low-resistance load in the subscriber station is then connected in parallel with the ringing load and the ringing current IL will increase.
  • This increase of the ringing current IL will cause a corresponding increase of the rectified current 14 as apparent from Fig. 2a.
  • the amplitude of the rectified current 14 exceeds the reference current 15 and the current comparator 4 begins to generate the current 13.
  • the current 13 causes the voltage VC in the node C to start to increase from zero or ground as shown in Fig. 2b. This increase of the voltage NC will continue as long as I4>15.
  • the voltage NC in the node C i.e. on the control input terminal of the current attenuator 3, causes the current attenuator 3 to attenuate the ringing currents II and 12, thereby lowering their amplitudes.
  • the peak value of 4 has been attenuated as apparent from Fig. 2a but still it exceeds 15.
  • the capacitor Cl is further charged by the current 13 and the current attenuator 3 is caused to further attenuate the ringing currents II and 12.
  • the peak value of 14 is supposed to equal 15.
  • the ringing current has very quickly been attenuated to a value that has been set such that there is no risk for the current amplifiers 5 and 6 to be damaged.

Landscapes

  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Interface Circuits In Exchanges (AREA)
  • Devices For Supply Of Signal Current (AREA)

Abstract

A ringing current (IL) in a subscriber Line interface circuit (1) is limited to a desired maximum value (I5) by a ringing current attenuator (3) having a control input terminal connected to a control output terminal of a current comparator (4). The comparator (4) compares a sensed value (I4) of the ringing current with the desired maximum value (I5). In response to that the sensed value (I4) exceeds the desired maximum value (I5), the attenuator (3) is controlled to reduce the ringing current such that its peak value is kept equal to or below the desired maximum value.

Description

METHOD AND ARRANGEMENT FOR LIMITING A RINGING CURRENT
TECHNICAL FIELD
The invention relates generally to subscriber line interface circuits (SLICs) and more specifically to ringing current limitation in SLICs.
BACKGROUND OF THE INVENTION
To comply with ringing specifications, a SLIC with integrated ringing must be able to apply a desired constant ringing voltage to a two-wire transmission line to which a subscriber station is connected.
The ringing voltage is applied across the subscriber station resistance, also called ringing load, in series with the transmission line resistance. Depending on the values of the ringing load and the line resistance, the ringing voltage causes a ringing current to flow in the transmission line.
The value of the ringing load is expressed as a Ring Equivalent Number (REN) that can vary between 0.1 REN and 5 REN, where 1 REN is about 7 kΩ.
When the subscriber station goes off-hook, a low-resistance load is connected in parallel with the ringing load inside the subscriber station, thereby reducing the subscriber station resistance. Since the ringing voltage is constant, the ringing current will increase and this condition will remain until the ringing signal is turned off.
To save chip area, it is desired to be able to use the output stages of the SLIC to generate the ringing signal. The necessary currents and voltages are within the operating range of the output stages. Normally, the output stages of the SLIC are used to supply current and speech signals to the subscriber station.
The SLIC is designed as a voltage amplifier and provides a desired ringing voltage. The ringing current is the ringing voltage divided by the load of the two-wire circuit. To generate a ringing signal, the output stages of the SLIC have to output a current of up to 100 mA. At an off-hook condition, i.e. when a low-resistance load in the subscriber station is connected in parallel with the ringing load, the ringing current will increase up to 300 mA. This causes a problem in the SLIC in that the power generated in the output stages can cause damage to them. The same is true in case of a fault condition, e.g. upon an unintentional grounding of one of the wires of the two- wire transmission line.
Thus, there is a need of ringing current limitation in SLICs in order to protect them.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method and an arrangement for ringing current limitation in a SLIC to limit the ringing current to a value just above the desired ringing current. The ringing current limitation method and arrangement should also quickly reduce the off-hook current or fault condition current and keep it at the desired level until the ringing signal is turned off.
This is attained according to the invention in that the ringing current is sensed relative to a reference current and reduced if it exceeds the reference current. The reference current is so chosen that there is no risk of damaging the output stages.
Thus, when a ringing current is injected into the SLIC, amplified and outputted to the two-wire circuit, it will be detected whether or not the ringing current exceeds the reference current, and if so, the ringing current will be reduced to a peak value equal to or below the reference current.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described more in detail below with reference to the appended drawing on which Fig. 1 is a block diagram of an embodiment of a ringing current limitation arrangement according to the invention in a schematically illustrated SLIC, and Figs. 2a and 2b illustrate waveforms in different nodes in the arrangement in Fig. 1. DESCRIPTION OF THE INVENTION
Fig. 1 schematically shows a SLIC 1 connected to wires A and B of a two- wire transmission line to a subscriber station (not shown). A load RL connected to the wires A and B in Fig. 1 represents a sum of the line resistance and the ringing load of the subscriber station.
An AC ringing signal intended for the subscriber station is injected into the SLIC 1 via an input terminal IN that is connected to an input terminal of a current amplifier 2. The current amplifier 2 has two output terminals and is adapted to output equal currents II and 12 to respective input terminals of a controllable current attenuator 3. The current attenuator 3 has one control input terminal connected via a node C to an output terminal of a current comparator 4, and two output terminals connected to input terminals of respective current amplifiers 5 and 6.
The node C is connected to ground via a capacitor Cl in parallel with a resistor Rl. The control input of the current attenuator 3 is of a high resistance. Thus, the current attenuator 3 is controlled by the voltage in node C.
The current attenuator 3 is adapted to output equal ringing currents II ' and 12' that are attenuated versions of the input currents II and 12, respectively, in response to the voltage in node C. In the absence of a voltage in node C, II ' = II and 12' = 12.
The current amplifiers 5 and 6 are adapted to amplify the ringing currents II ' and 12' by amplification factors +g and -g, respectively, before ringing currents IL and -IL, respectively, are applied to the wires A and B via the output terminals of the respective current amplifier 5 and 6.
A voltage controlled current source 8 is connected with its input terminals to the wires A and B, respectively, and with its output terminal to the input terminal of the current amplifier 2. The voltage controlled current source 8 senses the line voltage NL across the load RL and feeds a phase-inverted signal back to the current amplifier 2. Hereby, a fixed amplification is obtained between the injected ringing signal and the line voltage NL. Consequently, the ringing current IL will increase when the load RL is decreased e.g. when the subscriber station goes off-hook.
In accordance with the invention, a value of the ringing current IL is sensed by means of a current sensor 7 that, in the embodiment in Fig. 1, is interconnected between the output terminal of the current amplifier 5 and the wire A to sense an actual value of the ringing current IL.
However, it is to be understood that a value of the ringing current equally well can be sensed in another node as long as the relationship to the actual ringing current IL is known, e.g. on the input terminal of the current amplifier 5 where II ' = IL/g, i.e. where a portion of the ringing current IL is sensed.
The current sensor 7 is adapted to output a rectified version 14 of the ringing current IL to one input terminal of the current comparator 4. Another input terminal of the current comparator 4 is connected to a reference DC current source IREF that is adapted to output a fixed reference current 15. The reference current 15 represents the maximum allowable peak value of the ringing current IL and is set such that there is no risk for the ringing current to damage the output stages, i.e. the current amplifiers 5 and 6.
It should be pointed out that, if the ringing current is sensed on the input terminal of the current amplifier 5 as mentioned above, the reference DC current source IREF has to be scaled down to output the reference current I5/g.
If the current 14 exceeds the reference current 15, the current comparator 4 outputs a control current 13 to the node C. The current 13 charges the capacitor Cl and the capacitor Cl is discharged towards ground through the resistor Rl. The voltage caused by the current 13 in the node C, i.e. on the control input terminal of the current attenuator 3, controls the current attenuator 3 to attenuate the ringing currents II and 12 in proportion to the value of the voltage. The current 13 will be outputted by the current comparator 4 as long as the current 14 exceeds the reference current 15.
With reference to Figs. 2a and 2b, the operation of the embodiment of the ringing current limiting arrangement according to the invention, shown in Fig. 1 will be described.
Fig. 2a is a diagram of the rectified ringing current 14 supplied by the current sensor 7 to the current comparator 4 to be compared with the reference current 15 provided by the ' DC current source IREF.
At time tO, the subscriber station goes off-hook. As mentioned in the introductory portion above, a low-resistance load in the subscriber station is then connected in parallel with the ringing load and the ringing current IL will increase. This increase of the ringing current IL will cause a corresponding increase of the rectified current 14 as apparent from Fig. 2a.
At time tl, the amplitude of the rectified current 14 exceeds the reference current 15 and the current comparator 4 begins to generate the current 13. The current 13 causes the voltage VC in the node C to start to increase from zero or ground as shown in Fig. 2b. This increase of the voltage NC will continue as long as I4>15. The voltage NC in the node C, i.e. on the control input terminal of the current attenuator 3, causes the current attenuator 3 to attenuate the ringing currents II and 12, thereby lowering their amplitudes.
At time t2, 14<15. At that time, the discharge of the capacitor Cl to a lower voltage value begins as illustrated in Fig. 2b.
During the next half-period of the ringing current, the peak value of 4 has been attenuated as apparent from Fig. 2a but still it exceeds 15. Thus, the capacitor Cl is further charged by the current 13 and the current attenuator 3 is caused to further attenuate the ringing currents II and 12.
At time t3, the peak value of 14 is supposed to equal 15.
Thus, the ringing current has very quickly been attenuated to a value that has been set such that there is no risk for the current amplifiers 5 and 6 to be damaged.

Claims

1. A method of limiting a ringing current in a subscriber line interface circuit to a maximum value, characterized by
- sensing a value of the ringing current and comparing it with the maximum value to detect when the sensed value exceeds the maximum value,
- in response to that the sensed value exceeds the maximum value, generating a signal that is proportional to the difference between the sensed value and the maximum value, and
- attenuating the ringing current in response to said signal such that its peak value is kept equal to or below the maximum value.
2. The method according to claim 1, characterized by sensing an actual value of the ringing current.
3. An arrangement for limiting a ringing current in a subscriber line interface circuit to a maximum value, characterized in that it comprises a ringing current attenuator (3) having a control input terminal connected to a control output terminal of a current comparator (4), the comparator (4) being adapted to compare a sensed value of the ringing current with the maximum value and, in response to that the sensed value exceeds the maximum value, to supply to the attenuator (3) a control signal that is proportional to the difference between the sensed value and the maximum value to reduce the ringing current such that its peak value is kept equal to or below the maximum value.
4. The arrangement according to claim 3, characterized in that the sensed value is an actual value of the ringing current.
5. An arrangement for limiting a ringing current in a subscriber line interface circuit (1), comprising a first current amplifier (2) having an input terminal (IN) for receiving the ringing current, and two output terminals for outputting equal currents (II, 12) to input terminals of a pair of second current amplifiers (5, 6) whose output terminals are connected to respective wire of a two- wire circuit to a subscriber station (RL) for receiving the ringing current, characterized in that a current sensor (7) is provided to sense the ringing current (IL) or a portion thereof and to generate a rectified copy (14) of the sensed current (IL) on an output terminal connected to one input terminal of a current comparator (4), the current comparator (4) having another input terminal connected to a reference current source (IREF) generating a reference current (15), and an output terminal connected to a control input terminal of a current attenuator (3) interconnected between the output terminals of said first current amplifier (2) and the input terminals of said pair of second current amplifiers (5, 6), the current comparator (4) being adapted to supply a control current (13) to the current attenuator (3) when the sensed current (IL) exceeds the reference current (15) to attenuate said equal currents (II, 12) in correspondence to the difference between the sensed current (IL) and the reference current (15).
PCT/SE2002/000413 2001-03-09 2002-03-07 Method and arrangement for limiting a ringing current WO2002073936A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0100802-8 2001-03-09
SE0100802A SE0100802D0 (en) 2001-03-09 2001-03-09 Method and arrangement for limiting a ringing current

Publications (1)

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WO2002073936A2 true WO2002073936A2 (en) 2002-09-19

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TW (1) TW497346B (en)
WO (1) WO2002073936A2 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10240815A1 (en) * 2002-08-30 2004-03-18 Infineon Technologies Ag Telephone subscriber line calling signal current setting procedure compares measured current into subscriber load with preset value and adjusts generator supply voltage
WO2010063177A1 (en) * 2008-12-04 2010-06-10 中兴通讯股份有限公司 Telephone access device and channel driving method

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10240815A1 (en) * 2002-08-30 2004-03-18 Infineon Technologies Ag Telephone subscriber line calling signal current setting procedure compares measured current into subscriber load with preset value and adjusts generator supply voltage
DE10240815B4 (en) * 2002-08-30 2006-02-23 Infineon Technologies Ag Method for setting a call signal stream in a subscriber line and circuit arrangement
US7010120B2 (en) 2002-08-30 2006-03-07 Infineon Technologies Ag Method for adjusting a ringing signal current in a subscriber line and circuit arrangement
WO2010063177A1 (en) * 2008-12-04 2010-06-10 中兴通讯股份有限公司 Telephone access device and channel driving method

Also Published As

Publication number Publication date
TW497346B (en) 2002-08-01
SE0100802D0 (en) 2001-03-09

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