Telephonic communications – Subscriber line or transmission line interface
Patent
1997-03-19
1999-09-28
Le, N.
Telephonic communications
Subscriber line or transmission line interface
379398, 379413, H04M 100
Patent
active
059600764
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a method and to an arrangement for determining the deviation of a longitudinal signal component from a predetermined value on a balanced two-wire conductor.
2. Description of the Background Art
Subscriber apparatus are connected to switching centres by means of balanced two-wire conductors, so-called subscriber lines, each of which is connected in the switching centres to a respective subscriber line circuit in the form of a semi-conductor chip.
One function of the subscriber line circuit is to supply direct current to the subscriber line. The resultant voltage on the subscriber line is therewith load-dependent, i.e. subscriber apparatus dependent. In this regard, it is important that the mean value of the potentials on the signal conductors is kept constant. This is achieved traditionally, by maintaining the centre point between the two signal conductors at constant potential.
This is normally achieved by connecting over the subscriber line a voltage divider which includes two resistors of mutually the same size, so as to be able to detect the potential at the subscriber-line centre point. The potential obtained between the resistors in the voltage divider is compared with a reference value, which in turn is determined by a voltage divider between earth and the supply voltage of the subscriber line circuit. The measured difference is then allowed to activate the final stage of the subscriber circuit longitudinally. This feedback system forms the so-called longitudinal loop.
In a telephone switching centre, the subscriber lines are mostly at rest, i.e. the lines are open for most of the time. However, when the potential at the midway point of the subscriber line is detected with the aid of a voltage divider that has two resistors of mutually equal size in accordance with the aforesaid conventional method, the power loss in the resistors is greatest in the case of an open subscriber line. If the resistance values of the two resistors are increased in order to reduce power loss, it is necessary to increase the size of the chip. Thus, this known method always requires relatively wide surface demanding resistors. Although these resistors occupy a significant part of the surface of the subscriber line circuit, their contribution to the power loss when the lines are at rest is also significant.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to reduce the power loss in the subscriber line circuits at rest, and therewith reduce the total power loss in the telephone switching centre.
This object is achieved in accordance with the inventive method by measuring a first voltage between one wire and a first reference potential, by measuring a second voltage between the second wire and a second reference potential, and by determining the difference between the first and the second voltage values, this difference being proportional to the deviation of the longitudinal signal components from the mean value of the first and the second reference potentials.
The object is also achieved with the inventive arrangement, which includes a first voltage measuring means which functions to measure a first voltage between one wire and a first reference potential, a second voltage measuring means which functions to measure a second voltage between the other wire and a second reference potential, and a difference forming means which functions to form the difference between the first and the second voltages, this difference being proportional to the deviation of the longitudinal signal components from the mean value of the first and the second reference potentials.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail with reference to an exemplifying embodiment of an inventive arrangement and also with reference to the accompanying drawing.
BEST MODE OF CARRYING OUT THE INVENTION
The reference numerals 1 and 2 identify the two final stages in a subscriber line circuit (not shown in detail) for supplying
REFERENCES:
patent: 4852162 (1989-07-01), Taya et al.
patent: 4910768 (1990-03-01), Sue et al.
patent: 5347577 (1994-09-01), Takato et al.
Basic Engineering Circuit Analysis, 3rd Edition By J. David Irwin pp. 126-127, 1990.
IEEE Standary Dictionary of Electrical And Electronic Term, Sixth Edition, IEEE STD. 100-1996 pp.181, & 603.
Eriksson Hans Oskar
Hellberg Henrik
Larsson Elisabeth Maria
Malmgren Carl-Henrik Jorgen
Hsieh Shih-Wen
Le N.
Telefonaktiebolaget LM Ericsson
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