TERMINATION DEVICE FOR A TELEPHONE LINE

Abstract: A termination device for a telephone line of a wire based telephone system, said termination device (30) comprising: a high-pass filter (39) for separating signals within a frequency band used by a high-speed modem (13) for data transmission; and impedance means (53) connected to the high-pass filter (39), wherein said impedance means (53) has an impedance which matches the impedance of the telephone line in the frequency band used by the high-speed modem (13).

Description: Specification Termination device for a telephone line The present invention relates to a termination device for a telephone line of a wire-based telephone system, especially PBX-Systems having multiple telephone lines, wherein at least one telephone line comprises several telephone outlets. Many locations, for example homes, hotel rooms or offices frequently have multiple telephone outlets or sockets connected to the same telephone line of a telephone network. A high-speed modem, for example a VDSL-Modem, may be connected to one of the outlets in order to provide a high-speed data service. At the same time the other outlets of that telephone line may be connected to additional communication devices such as telephone apparatus, fax machine etc. or may be left unconnected. Figure 1 shows a room wall, for example of a hotel room, having telephone sockets A, B, C, D connected via telephone line T to a telephone network. A service splitter is connected to telephone socket A. The service splitter is a coupler that brakes a signal into multiple derived signals. The splitter splits an incoming signal co ing from socket A into outgoing signals on basis of the signal frequency. Voice signals which are transmitted in a low frequency range are separated from data signals which are transmitted in a high frequency range. The service splitter is connected to a modem and to a POTS or ISDN-Terminal. In POTS (POTS: plane old telephone system) voice data is transmitted within a low frequency range reaching from 0 Hz to about 3.4 kHz whereas in ISDN the voice data is transmitted within a frequency range reaching from 0 Hz to about 130 kHz. A telephone set is connected to the telephone terminal. The broadband-communication device such as a personal computer or a laptop is connected to the modem for data transmission. The modem shown in figure 1 is a high-speed mo- dem for example a VDSL-Modem (VDSL: very high-speed digital subscriber line) which is connected to the service splitter to provide a high-speed data service. DSL (DSL: digital subscriber line) provides a digital connection for customers or other end users . By using digital signalling methods both voice and data can be transmitted over conventional telephone wires but with a much higher speed than possible with ordinary modems. xDSL-Modems can be ADSL- Modems (ADSL: asymmetric digital subscriber line) , HDSL (HDSL: high-bit rate digital subscriber line) MDSL-Mode s (MDSL: medium bit rate digital subscriber line) or VDSL- Modems . xDSL-high-speed-modems transmit data in a high frequency range . Figure 2 shows in principle a frequency spectrum of signals transmitted via a conventional telephone line, wherein the voice signal is transmitted in a low frequency range and the data signal is transmitted in a high frequency range. The mo- dem sends data from the broadband-communication device via the service splitter and socket A to the telephone network (so called upstream) and receives data from the telephone network via socket A and the service splitter (so called downstream) in a downstream frequency band. The upstream and downstream frequency bands are separated by a guard band, wherein the guard band is preferably within the amateur radio band to avoid disturbances caused by amateur radio. High-speed-xDΞL-Modems receive data within the downstream- frequency band at a frequency which is very high and usually higher than 1 MHz . There is a functional relation between the propagation speed of the telephone signal V which is proportional to the prod- uct of the wavelength λ and frequency f: V ~ λ * f The wavelength λ of the signals transmitted via the telephone line becomes smaller when the frequency f increases. When the signals are transmitted in a very high frequency band as it is the case with xDSL-Modems the wavelength λ will be in the magnitude of several meters, i.e. having a size in the magnitude of walls in a building. Therefore signal reflections will occur at additional sockets to which no devices are connected and which are electrically connected via a wire to a telephone line T such as socket B in figure 1. These additional outlets are seen by the high-speed modem as stubs of wire which are connected to the main transmission telephone line T. These stubs reflect the signal in a manner that cause disturbing "notches" in the signal frequency spectrum. Figure 2 shows "notches" which are caused by sockets to which no device is connected and which reflect signals. The frequency of the caused "notch" fnotch and the severity of the notch are dependent on the length L of the extension wire shown in figure 1. In addition to the signal reflections at socket B further telephone sets which are connected to the other outlets C, D create when operated additional interference signals to the xDSL transmission in the xDSL data transmission frequency range. For example signals like clock signals from a cordless phone base station connected to socket D may disturb the xDSL data transmission. Accordingly it is the object of the present invention to provide a termination device which prevents signal disturbances in the data transmission of high-speed modems. This object is achieved by a termination device having the features of main claim 1. The termination device according to the present invention comprises a high-pass filter for separating signals within a frequency band used by a high speed modem, and impedance means connected to the high-pass filter, wherein said impedance means has an impedance that matches the impedance of the telephone line in the frequency band used by the high-speed modem. In a preferred embodiment of the present invention the termination device comprises a low-pass filter for separating telephone voice signals transmitted within a low frequency band. This provides the advantage that signal disturbances caused by a telephone set or a base station connected to the termination device are suppressed. In a preferred embodiment of the present invention the imped- ance of the impedance means is asymptotically resistive in the frequency domain. In a preferred embodiment the impedance is as resistor. The impedance is preferably a resistor having 130 Ohms. In a preferred embodiment of the present invention the low- pass filter and the high-pass filter are passive filters. In a preferred embodiment the cut-off frequency of the low- pass filter is about 700 kHz. In a preferred embodiment of the present invention the cutoff frequency of the high-pass filter is about 1 MHz . In an alternative embodiment the low-pass filter and the high-pass filter of the termination device according to the present invention are active filters. In a further embodiment of the present invention the low frequency band is a POTS-frequency band reaching from 0 Hz to about 4 kHz . In an alternative embodiment of the termination device ac- cording to the present invention the low frequency band is an ISDN-frequency band reaching from 0 Hz to about 130 kHz. In a preferred embodiment of the termination device according to the present invention the high-speed modem is an xDSL- modem. This xDSL-modem is preferably a VDSL-Modem. In a preferred embodiment of the present invention the fre- quency band used by the high-speed modem comprises a data downstream frequency band and a data upstream-frequency band. The data downstream-frequency band reaches preferably from about 0.9 MHz to about 3.5 MHz and the data upstream- frequency band reaches from about 4 MHz to about 7.9 MHz. The low-pass filter has according to a preferred embodiment an output terminal for connecting a telephone set to the termination device. In a preferred embodiment of the termination device according to the present invention the low-pass filter and the high- pass filter are connected in parallel to each other. The telephone line is in a preferred embodiment an unshielded twisted-pair cable (UTP) made of copper. In a further preferred embodiment of the termination device according to the present invention the termination device is switched automatically to an input terminal connected to the telephone line when no telephone set is connected to the ter- ination device. In a further embodiment the termination device includes detection means which detects whether a telephone set is connected to the termination device and controls a switching unit to connect the high-pass filter with the telephone line in case that no telephone set in connected. In a preferred embodiment of the termination device according to the present invention the impedance of the impedance means is adjustable. In a further embodiment of the termination device according to the present invention the termination device is integrated in a telephone socket. In an alternative embodiment the termination device is integrated in a telephone set . In a further alternative embodiment the termination device is integrated in a telephone jack. In a still further alternative embodiment the termination device is integrated in a telephone extension wire. Further preferred embodiments of the termination device according to the present invention are described in detail with respect to the figures for explanation of essential features of the invention. Figure 1 shows a telephone wiring structure for explanation of the problem underlying the present invention; Figure 2 shows a frequency spectrum for voice and data trans- mission for explanation of the problem underlying the present invention; Figure 3 shows a telephone wiring structure including several termination devices according to the present invention; Figure 4 shows a block diagram of a preferred embodiment of a termination device according to the present invention; Figure 5 shows a preferred embodiment of a termination device comprising passive filters according to the present invention. As can be seen from Figure 3 showing a telephone wiring structure there are provided in a room wall 1 several tele- phone sockets or telephone outlets 2, 3, 4, 5. Telephone socket 2 is connected via a line 6 to a service splitter 7 for separating telephone voice signals from data signals. The separated telephone voice signals are transmit- ted bi-directionally via a signal line 8 to a telephone terminal 9 to which the telephone set 10 is connected via a signal line 11. The data signal separated by the splitter 7 is transmitted via data signal line 12 to a high-speed modem 13 such as an xDSL-modem. The xDSL-modem includes an remote transmission unit 14 which is connected via line 15 to a terminal unit 16. A broadband-communication device such as a laptop or a personal computer 17 is connected via a line 18 to the ter ina- tion unit 16 of the high-speed modem 13. The socket 2 is connected via telephone wire 19 to a basement-transmitting unit 20 of a telephone network 21. The telephone wire 19 is usually an unshielded twisted-pair cable made of copper. In the room wall 1 are provided further sockets 3, 4, 5 which are connected to the telephone wire 19 via connecting wires 22, 23, 24, 25. Figure 3 just shows an example for a possible wiring structure within a room wall 1, however the number of sockets and the exact wiring may vary and is unknown. Connected to each of the additional sockets 3, 4, 5 a termination device 30 according to the present invention is connected via connecting lines 26, 27, 28. To termination device 30 b according the present invention a conventional telephone set 29 is connected via line 31. Further to termination device 30 c according to the present invention a cordless phone base station 32 is connected via line 33. The wiring structure can have any form such as a tree structure. As can be seen from figure 3 a termination device 30 according to the present invention is provided for every telephone socket 3, 4, 5, 6 with the exception of telephone socket 2 connected to the high-speed modem 13 through service splitter 7. The termination device 30 according to the present invention may be integrated in the telephone sockets 3, 4, 5. In alter- native embodiments the termination device 30 according to the present invention is integrated either in the telephone set, in a telephone jack or in a telephone extension wire. The termination device 30a shown in figure 3 prevents dis- turbing reflections from socket 3 via lines 22, 25 to the telephone wire 19 which might disturb the downstream data transmitted to the high-speed modem 13 in a high frequency band. The termination device 30 b as shown in figure 3 prevents signals which are created when the telephone set 29 is operated to cause interference with the xDSL data transmission in the xDSL high frequency range used by the high-speed modem 13. The termination device 30 c can prevent for example clock signals created by the cordless phone base station 32 from disturbing the xDSL data transmission signal within the xDSL high frequency data transmission range. The small termination devices 30 connected to sockets 3 to 5 suppress high frequency wavelike-effects like signal reflections and antenna effects which are disturbing factors effecting signal transmission over the telephone wire 19. Disturbing "notches" as shown in figure 2 are prevented by the small termination device 30 according to the present invention thus reducing data errors which might be caused by such "notches" . The termination devices 30a to 30c according to the present invention as shown in figure 3 can be adapters to be plugged in the sockets 3 to 5 or can be in an alternative embodiment be integrated in the sockets 3 to 5. The highspeed modem 13 shown in figure 3 can be any modem using a high frequency band in the telephone wire 19 for data transmission, i.e. any xDSL-modem. Figure 4 shows a block diagram of a preferred embodiment of the termination device 30 according to the present invention. The termination device 30 is for example connected to socket 3 shown in figure 4. Socket 3 comprises a pair of telephone wires 34, 35 to which the termination device 30 is connected via lines 36, 37. The connecting lines 36, 37 link a low-pass filter 38 to the telephone socket 3. A high-pass filter 39 is connected in parallel to the low-pass filter 38 by means of signal lines 40, 41. The termination device 30 comprise an input terminal 42, 43 to link the termination device 30 to the telephone socket 3 via lines 36, 37. The low-pass filter 38 is further connected via lines 44, 45 to terminals 46, 47 of the termination device 30. A telephone set 48 can be connected the terminals 46, 47 of the termination device 30 via lines 49, 50. The telephone set 48 might be plugged into the termination device but the termination device 30 according to the present invention works also when no telephone set 48 is connected to the low-pass filter 38. The high-pass filter 39 is connected via lines 51, 52 to impedance means 53. Impedance means 53 connected to the high-pas filter 39 comprises an impedance that matches the impedance of the telephone line used by the telephone network system and the frequency band used by the high-speed modem 13. The impedance of the impedance means 53 is not a complex impedance but a real impedance . The values of the impedance means 53 depend on the impedance of the telephone line of the used telephone system. In Germany the impedance of impedance means 53 is 130 Ohms. The low-pass filter 38 and the high-pass filter 39 can either be passive or active filters. Passive filters are preferred because the production costs are lower and no power supply for the filters is necessary. The cut-off frequency of the filters are in a preferred embodiment adjustable. The cut-off frequency of the low-pass filter 38 within a preferred embodiment is about 700 kHz and the cut-off frequency of the high-pass filter 39 is about 1 MHz. The low-pass filter 38 is provided for separating telephone voice signals transmitted bi-directionally to the telephone set 48 within a low frequency band. The low frequency band can be a POTS-frequency band which reaches from 0 Hz to about 4 kHz or in an alternative embodiment can be a ISDN-frequency band reaching from 0 Hz to 130 kHz. The high-pass filter 39 is provided for separating signals occurring on line 22 within a frequency band used by the high-speed modem 13 for data transmission. This high-speed modem 13 can be any xDSL- modem and in particular a VDSL- modem. The high frequency band used by the high-speed modem 13 as shown in figure 3 comprises a data downstream frequency band and a data upstream frequency band as shown in figure 2. The data downstream frequency band between frequency fi and frequency f 2 ranges in preferred embodiment from about 0.9 MHz to about 3.5 MHz and the data upstream frequency band between frequencies f 3 , f reaches in a preferred embodiment from about 4 MHz to about 7.9 MHz . The cut-off frequencies of the low-pass filter 38 and the high-pass filter 39 are dimen- sioned depending on the high frequency band ranges used by the high-speed modem 13 for data transmission. In a preferred embodiment the high-pass filter 39 is switched automatically by means of a switching unit to the telephone socket 3 when no telephone set such as telephone set 48 is connected to the termination device 30. To this end the termination device 30 includes in a preferred embodiment detection means which detects whether the telephone set 48 is connected to the termination device 30, wherein the detection means controls the switching unit to connect the high-pass filter 39 with the telephone socket 3 is case that no telephone set 48 is connected to the termination device 30. In a further preferred embodiment the impedance of the imped- ance means 53 is adjustable. This impedance and the cut-off frequencies of the termination device 30 can be adjusted to the requirements of the telephone network within a country such as Germany and the United States. Figure 5 shows a preferred embodiment of a termination device 30 according to the present invention having a passive low- pass filter 38 and a passive high-pass filter 39. The low- pass filter 38 and the high-pass filter 39 includes only passive components . The passive components comprise capacitors and induetivities . Both filters 38, 39 do not need any power supply and can be produced at low costs. Low-pass filter 38 comprises inductivities 54, 55, 56, 57 connected in series between lines 42 and 46. Further, low- pass filter 38 comprises inductivities 58, 59, 60, 61 connected in series between terminal 43 and terminal 47. Further the low-pass filter 38 includes inductivities 62, 63, 64 connected in series to capacitors 65, 66, 67. The high-pass filter 39 comprises two capacitors 62, 63 connected in series between terminal 42 and line 51. Further high-pass filter 39 includes two 64, 65 also connected in series between terminal 43 and line 52. Furthermore high-pass filter 39 as shown in figure 5 has a capacitor 66 connected to an inductivity 67. In a preferred embodiment as shown in figure 5 both filters have inductivities and filters with fixed values. In an alternative embodiment the components within the filters 38, 39 are adjustable to vary the cut-off frequency of the filters. As becomes evident from figure 5 the termination device 30 according to the present invention includes only passive components and can be therefore pro- duced in a highly integrated manner making the termination device 30 according to the present invention a component which has a very small size. Further the production costs for the termination device 30 as shown in figure 5 are very low. The termination device 30 according to the present invention overcomes disturbing effects in a location with multiple telephone outlets connected to the same telephone line 19 where a high-speed modem 13 especially a VDSL-modem is also connected to that telephone line via an outlet 2. The termi- nation device 30 maintains the functionality and increases the available quality and available maximum transmission distance of the high-speed data transmission service. The avail- O 01/91439 13 able quality is increased by lowering the bit error rate caused by signal notches in the downstream data transmission frequency band or in the upstream data transmission frequency band. Furthermore the termination device 30 according to the present invention can be produced at low costs and small size. This has the additional advantage that the termination device 30 according to the present invention can be integrated into telephone sockets, the telephone jack a within the telephone set itself.

Claims: Claims 1. A termination device for a telephone line of a wire based telephone system, said termination device (30) comprising: a high-pass filter (39) for separating signals within a frequency band used by a high-speed modem (13) for data transmission; and impedance means (53) connected to the high-pass filter (39), wherein said impedance means (53) has an impedance which matches the impedance of the telephone line in the frequency band used by the high-speed modem (13) . 2. The termination device according to claim 1 further comprising a low-pass filter (38) for separating a telephone voice signal transmitted within a low frequency band. 3. The termination device according to claim In or 2, wherein the impedance of said impedance means (53) is asymptotically resistive. 4. The termination device according to claim 3, wherein the impedance means (53) is a resistor. 5. The termination device according to claim 4, wherein the impedance of the resistor (53) is 130 Ohms. 6. Termination device according to claim 1, wherein the low-pass filter (38) and the high-pass filter (39) are passive filters. 7. The termination device according to one of the preceding claims, wherein the cut-off frequency of the low-pass filter (38) is about 700 kHz. 8. The termination device according to one of the preceding claims, wherein the cut-off frequency of the high-pass filter (39) is about 1 MHz . 9. The termination device according to claim 1, wherein the low-pass filter (38) and the high-pass filter (39) are active filters. 10. The termination device according to one of the preceding claims, wherein the low frequency band is a POTS-frequency band reaching from 0 Hz to about 4 kHz . 11. The termination device according to one of the preceding claims 1 to 9, wherein the low frequency band is an ISDN-frequency band reaching from 0 Hz to 130 kHz. 12. The termination device according to one of the preceding claims, wherein the high-speed modem (13) is a xDSL-modem. 13. The termination device according to claim 12, wherein the xDSL-modem is a VDSL-modem. 14. The termination device according to one of the preceding claims, wherein the frequency band used by the high-speed modem (13) comprises a data downstream frequency band and a data upstream frequency band. 15. The termination device according to claim 14, wherein the data downstream frequency band reaches from about 0.9 MHz to about 3.5 MHz and the data upstream frequency band reaches from about 4 MHz to about 7.9 MHz . 16. The termination device according to one of the preceding claims, wherein the low-pass filter (38) has an output terminal (46, 47) for connecting a telephone set (48) to the termination device (30) . 17. The termination device according to one of the preceding claims , wherein the low-pass filter (38) and the high-pass filter (39) are connected in parallel to each other and to an input terminal (42, 43) of the termination device (30). 18. The termination device according to one of the preceding claims, wherein the telephone line is an unshielded twisted-pair cable (UTP) . 19. The termination device according to one of the preceding claims, wherein the high-pass filter (39) is switched automatically to the input terminal (42, 43) when no telephone set (48) is connected to the termination device (30) . 20. The termination device according to one of the preceding claims, wherein the termination device (30) includes a detection means which detects whether a telephone set is connected to the termination device and controls a switching unit to con- nect the high-pass filter (39) to the input terminal (42, 43) in case that no telephone set (48) is connected the termination device (30) . 21. The termination device according to one of the preceding claims, wherein the impedance of said impedance means (43) is adjustable. 22. The termination device according to one of the preceding claims , wherein the termination device (30) is integrated in a tele- phone socket . 23. The termination device according to one of the preceding claims 1 to 21, wherein the termination device (30) is integrated in a tele- phone set. 24. The termination device according to one the preceding claims 1 to 21, wherein the termination device (30) is integrated in a tele- phone jack, . 25. The termination device according to one of the preceding claims 1 to 21, wherein the termination device (30) is integrated in a tele- phone extension wire. 26. The termination device according to one of the preceding claims, wherein the cut-off frequency of the low-pass filter (38) and the high-pass filter (39) is adjustable.

Inventors: PONTE ELIYAHU, REUVEN YOSSEF, PONTE, ELIYAHU, REUVEN, YOSSEF
Applicants: INFINEON TECHNOLOGIES AG, PONTE ELIYAHU, REUVEN YOSSEF, PONTE, ELIYAHU, REUVEN, YOSSEF
Application year: 2000
Main classification: H04M11
IPC codes: H03H7, H04B3, H04B15, H04L27, H04M1, H04M11