Digital access arrangement circuitry and method for connecting to phone lines having a DC holding circuit with low distortion and current limiting

• US 6,516,024 B1
• Filed: 06/16/1998
• Issued: 02/04/2003
• Est. Priority Date: 04/22/1997
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Scott, Jeffrey W., Welland, David R., Tuttle, George Tyson, Dupuis, Timothy J., Sooch, Navdeep S.
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/098,252
• Time in Patent Office: 1,694 Days
• Field of Search: 375/257, 375/259, 375/285, 375/295, 375/296, 375/316, 375/340, 375/342, 375/354, 375/371, 375/220, 379/90.01, 379/393-399, 379/412
• US Class Current: 375/220
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: H04M 11/06 Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
• CPC Class Codes: H04M 19/001 Current supply source at the exchanger providing current to substations
• CPC Class Codes: Y02D 30/70 in wireless communication networks

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. Further, the current limiting mode includes a distortion adjustment circuit to limit distortion at a crossover point at which current limiting effects occur.

Claims

1. A communication system, comprising:

phone line side circuitry capable of being coupled to phone lines;

powered side circuitry capable of being coupled to the phone line side circuitry through an isolation barrier;

a DC holding circuit within the phone line side circuitry, the DC holding circuit being programmable in response to data transmitted across the isolation barrier to operate the DC holding circuit in a plurality of modes, the DC holding circuit operable in at least a first mode to meet a first phone line interface standard and a second mode to meet a second phone line interface standard, the second phone line interface standard having a DC current limit requirement; and

a distortion adjustment circuit within the DC holding circuit.

2. The communication system of claim 1, the DC holding circuit comprising a phone line side integrated circuit and at least one external device, the external device dissipating more power in the second mode than in the first mode.

3. The communication system of claim 1, further comprising the isolation barrier coupled between the phone line side circuitry and the powered side circuitry, the isolation barrier being a capacitive barrier.

4. The communication system of claim 1, wherein the phone line side circuitry and the powered side circuitry are configured to communicate across the isolation barrier through digital signals.

5. The communication system of claim 4, further comprising the isolation barrier coupled between the phone line side circuitry and the powered side circuitry, the isolation barrier comprising one or more capacitors.

6. The communication system of claim 1, wherein the DC holding circuit has at least two different impedances when operating in the second mode, the distortion adjustment circuit operable to limit distortion at a transition between the two impedances when the DC holding circuit is in the second mode.

7. The communication system of claim 6 wherein a substantial portion of the power dissipated by the DC holding circuit in the second mode is dissipated external to the phone line side integrated circuit.

8. The communication system of claim 7, wherein 50% or more of the power dissipated by the DC holding circuit is dissipated external to the phone line side integrated circuit.

9. The communication system of claim 8, wherein 50% or more of the power dissipated by the DC holding circuit is dissipated in one or more passive external devices.

10. The communication system of claim 9, wherein the one or more passive external devices are one or more resistors.

11. A method of providing a communication system capable of being coupled to a phone line, comprising:

coupling an isolation barrier between powered circuitry and phone line side circuitry;

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;

providing a programmable circuit for switching the DC holding circuit between at least a first and second mode of operation, the first mode of operation for at least a first phone line interface standard and the second mode of operation for at least a second phone line interface standard, the second standard having a DC termination current limit;

coupling the internal circuitry and external circuitry so that if the DC holding circuit is operated in the second mode of operation more power may be dissipated in the external circuitry during the second mode of operation than during the first mode of operation;

providing at least two different impedance levels for the DC holding circuit when the DC holding circuit is operated within the second mode of operation; and

adjusting distortion effects caused by a transition between the at least two different impedance levels.

12. The method of claim 11, further comprising utilizing a capacitive barrier to isolate the powered circuitry and the phone line circuitry.

13. The method of claim 11, further comprising passing digital data across the isolation barrier.

14. The method of claim 13, further comprising utilizing a capacitive barrier to isolate the powered circuitry and the phone line circuitry.

15. The method of claim 11, the adjusting distortion effects further comprising compensating for the effects of AC signals within the DC holding circuit.

16. The method of claim 15, the adjusting distortion effects further compensating for the clipping of AC signals.

17. A DC holding circuit for reducing power dissipation requirements of an integrated circuit within a communication system capable of being connected to phone lines, the DC holding circuit comprising:

at least one switchable circuit, the switchable circuit having a first state for a non-current limiting mode of operation and a second state for a current limiting mode of operation;

external circuitry external to the integrated circuit;

internal circuitry within the integrated circuit, the external circuitry and the internal circuitry being coupled together wherein the external circuitry dissipates more power in the current limiting mode than in the non-current limiting mode; and

distortion adjustment circuitry coupled to the internal circuitry, the distortion adjustment circuitry operable at least when the DC holding circuit is in the current limiting mode.

18. The DC holding circuit of claim 17, the DC holding circuit having at least two impedance levels when the DC holding circuit is in the current limiting mode of operation.

19. The DC holding circuit of claim 18, the distortion adjustment circuitry limiting distortion occurring when the DC holding circuit is operating close to a transition point between two of the at least two impedance levels.

20. A method of providing a DC holding circuit, comprising:

forming the DC holding circuit with internal circuitry internal to an integrated circuit and external circuitry external to the integrated circuit;

providing a programmable circuit for switching the DC holding circuit between at least a first and second mode of operation, the first mode of operation for at least a first phone line interface standard and the second mode of operation for at least a second phone line interface standard, the second standard having a DC termination current limit;

coupling the internal circuitry and external circuitry so that if the DC holding circuit is operated in the second mode of operation more power is capable of being dissipated in the external circuitry during the first mode of operation than during the second mode of operation;

providing at least two different impedance levels for the DC holding circuit when the DC holding circuit is operated within the second mode of operation; and

adjusting distortion effects caused by a transition between the at least two different impedance levels.

21. The method of claim 20, the adjusting distortion effects further comprising compensating for the effects of AC signals within the DC holding circuit.

22. The method of claim 21, the adjusting distortion effects further compensating for the clipping of AC signals.

23. The method of claim 22, the compensation of clipping of AC signals comprising providing an additional signal having substantially the opposite waveform of a clipped AC signal.

24. A method of forming a DC holding circuit, comprising:

providing integrated circuitry and non-integrated circuitry to comprise the DC holding circuit, the DC holding circuit capable of meeting at least at least a first and second phone line interface standards, the at least two phone line interface standards having differing current limit specifications, the second standard limiting DC current to a lower amount than the first standard;

utilizing at least one switchable circuit so that the DC holding circuit is capable of being programmed for at least one of the phone line interface standards;

coupling the integrated circuitry and the non-integrated circuitry together so that when the DC holding circuit is programmed for the second phone line interface standard, at least one circuit element of the external circuitry will receive additional DC current as compared to when the DC holding circuit is programmed for the first phone line interface standard;

providing a plurality of DC impedance levels for the DC holding circuit when the DC holding circuit is programmed for the second phone line interface standard; and

limiting distortion at a crossover point between at least two of the plurality of DC impedance levels.

25. The method of claim 24, the limiting of distortion further comprising compensating for the effects of AC signals within the DC holding circuit.

26. The method of claim 25, the limiting of distortion further compensating for the clipping of AC signals.

27. A DC holding circuit within a communication system capable of being connected to phone lines, the DC holding circuit compatible with a phone line interface standard that has a DC current limit requirement, the DC holding circuit comprising:

a first impedance level present at one or more inputs of the DC holding circuit for a first set of DC loop current values;

a second impedance level present at the one or more inputs of the DC holding circuit for a second set of DC loop current values; and

distortion adjustment circuitry within the DC holding circuit, the distortion adjustment circuitry operable to limit distortion during transitions between the first and second impedance levels.

28. The DC holding circuit of claim 27, the distortion adjustment circuitry compensating for clipping of AC signals.

29. A method of providing a DC holding circuit, comprising:

providing at least two different impedance levels for the DC holding circuit when the DC holding circuit is operated in a DC current limit mode; and

adjusting distortion effects caused by a transition between the at least two different impedance levels.

30. The method of claim 29, the adjusting distortion effects further comprising compensating for the effects of AC signals within the DC holding circuit.

31. The method of claim 30, the adjusting distortion effects further compensating for the clipping of AC signals.

32. The method of claim 31, the compensation of clipping of AC signals comprising providing an additional signal having substantially the opposite waveform of a clipped AC signal.

33. A method of operating a DC holding circuit, comprising:

providing a plurality of DC impedance levels for the DC holding circuit when the DC holding circuit is operated to satisfy a DC current limit standard; and

limiting distortion at a crossover point between at least two of the plurality of DC impedance levels.

34. The method of claim 33, the limiting of distortion further comprising compensating for the effects of AC signals within the DC holding circuit.

35. The method of claim 34, the limiting of distortion further compensating for the clipping of AC signals.