Digital access arrangement circuitry and method for connecting to phone lines having a DC holding circuit with switchable DC termination impedance
First Claim
1. A communication system, comprising:
- phone line side circuitry, at the user end of phone lines, capable of being coupled to phone lines;
powered side circuitry, at the user end of phone lines, capable of being coupled to the phone line side circuitry through an isolation barrier; and
a DC holding circuit within the phone line side circuitry, the DC holding circuit being changeable to have a plurality of DC termination impedances, the DC termination impedance being changeable based upon a detected DC loop current level, the DC loop current level detected by the phone line side circuitry,the DC holding circuit comprising a phone line side integrated circuit and at least one external device,wherein in at least one mode of operation more than 50% of the power dissipated by the DC holding circuit is dissipated external to the phone line side integrated circuit.
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Accused Products
Abstract
A digital direct access arrangement (DAA) circuitry may be used to terminate the telephone connections at the user'"'"'s end that provides a communication path for signals to and from the phone lines. Briefly described, the DAA provides a programmable means for the DC termination for a variety of international phone standards. The invention may also be utilized with means for transmitting and receiving a signal across a capacitive isolation barrier. More particularly, a DC holding circuit is provided in which a programmable DC current limiting mode is available. In the current limiting mode, power may be dissipated in devices external to a DAA integrated circuit. Moreover, much of the power may be dissipated in external passive devices, such as resistors.
157 Citations
13 Claims
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1. A communication system, comprising:
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phone line side circuitry, at the user end of phone lines, capable of being coupled to phone lines; powered side circuitry, at the user end of phone lines, capable of being coupled to the phone line side circuitry through an isolation barrier; and a DC holding circuit within the phone line side circuitry, the DC holding circuit being changeable to have a plurality of DC termination impedances, the DC termination impedance being changeable based upon a detected DC loop current level, the DC loop current level detected by the phone line side circuitry, the DC holding circuit comprising a phone line side integrated circuit and at least one external device, wherein in at least one mode of operation more than 50% of the power dissipated by the DC holding circuit is dissipated external to the phone line side integrated circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of providing a communication system capable of being coupled to a phone line, comprising:
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coupling an isolation barrier between powered circuitry and phone line side circuitry at the user end of phone lines; forming a DC holding circuit within the phone line side circuitry, the DC holding circuit comprising a phone line side integrated circuit and external circuitry external to the integrated circuit; and providing a circuit for switching the DC termination impedance of the DC holding circuit between at least two different impedance values, the two different impedance values being selectable based upon a detected DC loop current, the DC loop current level detected by the phone line side circuitry, wherein a first mode of operation is provided for a first phone line interface standard and a second mode of operation is provided d phone line interface standard, the DC termination impedance being switchable in the second mode of operation, and wherein the DC termination impedance is not switchable in the first mode of operation. - View Dependent Claims (9, 10, 11)
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12. A phone line interface circuit, comprising:
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phone line side circuitry capable of being coupled to phone lines at the user end of phone lines; and a DC holding circuit within the phone line side circuitry, the DC holding circuit being changeable to at least two different DC termination impedance values based upon a monitored DC loop current level, the DC loop current level being monitored by phone line side circuitry, the at least two different DC termination impedance values differing in value by at least 750 ohms, wherein in at least one mode of operation the DC termination impedance does not change based upon a DC loop current level. - View Dependent Claims (13)
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Specification