Telephonic communications – Line equalization or impedance matching
Reexamination Certificate
1997-09-26
2001-10-09
Woo, Stella (Department: 2643)
Telephonic communications
Line equalization or impedance matching
C379S399010
Reexamination Certificate
active
06301356
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a line circuit for matching an impedance used in telecommunication equipment, such as fax machines, modems, trunk line units, or in measuring equipment, such as generators thereof, or in measuring devices controlling e.g. the level of power or disturbance. The invention relates further to a method for the same.
BACKGROUND OF THE INVENTION
In analog and digital transmission systems the transmitted voice, sound, data etc. has to be terminated to different impedances. For example, in an analog trunk line unit the input impedance has to be selected e.g. between a resistive and complex impedances. From these the resistive impedance is an ohmic resistance and the complex impedance is a more complicated combination of ohmic resistances and capacitances. Sometimes even inductances form a part of the latter. The numeric values thereof might be such as e.g. 600 &OHgr;(res.) or 220 &OHgr;+(820 &OHgr;//115 nF) (complex), respectively.
The known designs have used straps, mechanical switches or mechanical relays for setting i.e. matching the suitable impedance. Such means need to be turned (switched) on and off manually e.g. by a service man. If the set impedance level is not in the predetermined level an echo effect will exist. In addition, there is always a risk that such mechanical means are switched to a wrong position. This might even happen accidentally after the initial, per se correct settings. From these known means the relays might be software controllable, but the power dissipation, size and lifetime thereof has not proven to be at a acceptable level. The use of so called optorelays is not adequate, as optorelays of good quality are expensive and as the on-state-resistance thereof will affect the termination impedance.
When selecting impedance said on-state-resistance should be zero. On-state-resistance means a unidealality of a switch, i.e. the value of the ohmic resistance over the switch as the switch or relay “draws” i.e. switches. In mechanical relays said value is almost zero, but such relays have various other disadvantages, such as the size, the slow switching speed and overheating problems. Therefore other solutions have been sought, and in many applications said resistance has been accepted to avoid the use of the mechanical relays.
The term ‘terminating point’ is usually used for a point in which the termination impedance can be seen against the ground. The value of the termination impedance in the terminating point may vary according to the overall system used and the national and international recommendations or requirements in various market areas and countries. For example, a similar termination impedance is not in use in Germany and in USA. In the following the term ‘market’is intented to generally mean one such country, market area or similar having an impedance of its own.
For the better understanding of the invention, a brief explanation of the directions in which a signal may move in a terminating point of a signal path is also given herein for three alternative events, i.e. for 1) terminating impedance, 2) output impedance, and for 3) input impedance. In the event of the terminating impedance 1), the signal moves both in and out in the terminating point. This kind of use is common for example in telephone equipments in which the users may listen and speak simultaneously, in fax machines, modems, trunk line units etc. When used as an output impedance 2), the signal moves only out from the terminating point. This kind of use is common, for instance, in generators or measuring devices which generate an output signal (e.g. 1014 Hz, 245 mV) at a given impedance level (e.g. 600 &OHgr;). The third possibility, i.e. input impedance 3), is commonly used e.g. in level meters of measuring devices metering the voltage level of an input signal (power level, disturbance level etc.). In this case the signal moves only to the ‘in’ direction at the terminating point.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the disadvantages of the prior art solutions and to provide a new type of solution for the setting of an impedance.
An object of the present invention is also to provide a method and arrangement in which the same circuitry can be set in accordance with different requirements set by the different markets by means of software based control means.
Another object of the present invention is to provide a method and an arrangement, by means of which the size and the power dissipation of the tele-equipment can be reduced and the reliability thereof can be enhanced.
It is also an object of the present invention to provide a method and an arrangement, by means of which the costs of the tele-equipment (or switch means) can be reduced.
It is also an object of the present invention to provide an arrangement in which the effect of switch tolerances on impedance accuracy can be reduced.
A still further object of the present invention is to provide an arrangement which is suitable for tele-equipment and apparatus.
A still further object of the present invention is to provide an arrangement which is suitable for analog telephone lines having a high number of different, alternative impedances.
Other objects and advantages of the present invention will be brought out in the following part of the specification taken in conjunction with the accompanying drawings.
The objects are obtained by providing a line circuit according to the present invention in order to have a certain impedance to a signal path. According to one alternative embodiment, said circuit comprises a first line and a second (input) line and a terminating point in said first line. At least one impedance determining circuit is connected between said lines. Said impedance circuit includes at least one operational amplifier, at least one multiplexer controllable by a control unit and at least one impedance net. According to the invention, the connection of said impedance circuit is arranged such that an output of the operational amplifier is connected to an inverting input thereof, while said impedance net is connected between the output of said amplifier and said terminating point of the line circuit, the arrangement being such that a non-inverting input of the operational amplifier is connectable by at least one respective multiplexer either to the terminating point or to said second (input) line.
The inventive method comprises the following steps: Connecting said at least one impedance circuit such that an output of the operational amplifier will become connected to an inverting input thereof, connecting the impedance net between the output of said amplifier and said terminating point, and connecting a non-inverting input of said operational amplifier by a respective multiplexer either to said terminating point or to said second line.
According to another embodiment a line circuit for matching impedance in order to have a certain impedance to a signal path is provided, said circuit comprising a line, at least one impedance determining circuit connected to said line, said at least one impedance circuit including at least one operational amplifier and at least one multiplexer controllable by a control unit and at least one impedance net. The connection of said at least one impedance circuit is arranged such that an output of the operational amplifier is connected to an inverting input thereof, said impedance net being connected between the output of said amplifier and said line. The arrangement is such that a non-inverting input of the operational amplifier is connectable by at least one respective multiplexer to said line.
According to the alternative embodiment of the present invention, a method is disclosed for matching impedance in a line circuit in order to have a certain impedance to a signal path. Said circuit comprises a line, at least one impedance determining circuit connected to said line, said at least one impedance circuit including at least one operational amplifier and at least one multiplexer controllable by a cont
Hyvakka Jouko
Takala Teijo
Burns Doane Swecker & Mathis L.L.P.
Telefonaktiebolaget LM Ericsson (publ)
Woo Stella
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