Digital access arrangement circuitry and method having a synthesized ringer impedance for connecting to phone lines

• US 6,522,745 B1
• Filed: 07/02/1999
• Issued: 02/18/2003
• 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, Sooch, Navdeep S.
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): SINGH, RAMNANDAN P
• Application Number:
  US09/347,688
• Time in Patent Office: 1,327 Days
• Field of Search: 379/373, 379/377, 379/398, 379/399, 379/405, 379/412, 379/413, 379/379, 341/110, 341/143, 375/219, 375/259, 455/554-559
• US Class Current: 379/399.01
• 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

Abstract

A digital direct access arrangement (DAA) circuitry may be used to terminate the telephone connections at the user'"'"'s end to provide a communication path for signals to and from the phone lines. Briefly described, a means for providing a proper ringer impedance for a variety of international phone standards while also providing a proper isolation barrier to the phone line is disclosed. More particularly, a DAA circuitry may be utilized which satisfies many or all ringer impedance standards without the use of additional discrete impedance devices. The ringer impedance standards may be satisfied by use of an impedance structure coupled between the TIP and RING lines and actively controlling the current drawn through the hookswitch devices when a ringing event is detected so as to control the impedance seen at the TIP and RING lines during a ringing event. The detection of the ringing event may be performed on the phone line side of an isolation barrier. By controlling the current drawn from the phone lines with the hookswitch circuitry, an impedance placed in parallel with the TIP and RING lines may in effect be synthesized. In one embodiment the impedance of the impedance structure may be infinity (i.e., the impedance structure across the TIP and RING lines is not utilized). In this case, the current drawn through the hookswitch will sufficiently synthesize an impedance across (or in parallel with) the TIP and RING lines that dominates and effectively sets the impedance seen at the TIP and RING lines. The DAA may also include means for transmitting and receiving a signal across a capacitive isolation barrier.

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; and

hookswitch circuitry within the phone line side circuitry, the hookswitch circuitry drawing current during ringer events to synthesize a ringer impedance.

2. The communication system of claim 1, further comprising a ring detect signal coupled to the hookswitch circuitry, the ring detect signal controlling the hookswitch circuitry to activate the current drawn through the hookswitch circuitry during ringer events.

3. The communication system of claim 2, further comprising an impedance structure coupled between the phone lines.

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

5. The communication system of claim 2, the system being country programmable to selectively draw the current.

6. The communication system of claim 1, the system being country programmable to selectively draw the current.

7. 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.

8. 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, wherein the digital signals include a digital phone line data stream multiplexed with control data before the digital signals are sent across the isolation barrier.

9. The communication system of claim 8, 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.

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

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

providing hookswitch circuitry within the phone line side circuitry; and

generating a substantial portion of a ringer impedance seen at the phone line by drawing current through the hookswitch circuitry.

11. The method of claim 10, further comprising utilizing a capacitive barrier to isolate the powered circuitry and the phone line circuitry.

12. The method of claim 11, further comprising passing digital signals across the isolation barrier.

13. The method of claim 12 wherein the digital signals include a digital phone line data stream multiplexed with control data before the digital signals are sent across the isolation barrier.

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

15. The method of claim 14, further comprising controlling the current drawn through the hookswitch circuitry during a ringing event through the use of ring detect circuitry.

16. The method of claim 15, further comprising providing a portion of the ringer impedance with an impedance structure coupled to the phone line.

17. The method of claim 15, wherein the current drawn through the hookswitch exceeds 1 mA.

18. A ringer impedance circuit within a communication system capable of being connected to phone lines, the ringer impedance circuit comprising:

a ringer detect signal; and

at least one impedance generating circuit coupled to the ringer detect signal, the at least one impedance generating circuit responsive to the ringer detect signal to provide a ringer impedance.

19. The ringer impedance circuit of claim 18, the impedance generating circuit being a hookswitch circuit.

20. The ringer impedance circuit of claim 18, wherein the impedance generating circuit synthesizes an impedance at the phone lines by drawing current from the phone line.

21. The ringer impedance circuit of claim 20, the impedance generating circuit being a hookswitch circuit.

22. The ringer impedance circuit of claim 20, a majority of the ringer impedance at the phone line being an effective impedance generated by the impedance generating circuit.

23. The ringer impedance circuit of claim 20, the hookswitch circuit including at least one transistor.

24. The ringer impedance circuit of claim 18, further comprising an impedance structure coupled to the phone lines, the impedance structure providing an impedance independent of the ring detect signal.

25. A method of providing a ringer impedance capable of satisfying a plurality of ringer impedance standards, comprising:

generating a ring detect signal; and

adjusting the ringer impedance present at a phone line in response to the ring detect signal.

26. The method of claim 25, wherein said adjusting comprises altering the current flow through at least one circuit coupled to the phone line.

27. The method of claim 26, wherein the at least one circuit comprises a hookswitch circuit.

28. The method of claim 27, wherein the current flow exceeds 1 mA.

29. A method of generating a ringer impedance for a phone line, comprising:

actively controlling at least one circuit of a DAA circuit; and

substantially setting the ringer impedance present at the phone line by the active control of the at least one circuit.

30. The method of claim 29, wherein the actively controlling further comprises adjusting the current flow through the at least one circuit.

31. The method of claim 30, wherein the at least one circuit comprises at least a portion of a hookswitch circuit.

32. The method of claim 29, wherein the actively controlling further comprises controlling the at least one circuit in response to detecting a ringer event.

33. The method of claim 32, wherein the actively controlling further comprises adjusting the current flow through the at least one circuit.

34. The method of claim 33, wherein the at least one circuit comprises at least a portion of a hookswitch circuit.

35. An integrated circuit compatible with a plurality of phone line standards having ringer impedance requirements, the integrated circuit comprising:

a ringer detect signal; and

at least one control signal generated in response to the ringer detect signal, the control signal operable to adjust the ringer impedance present at a phone line.

36. The integrated circuit of claim 35, the control signal capable of adjusting the current flow through at least one circuit coupled to the phone line so as to adjust the ringer impedance.

37. The integrated circuit of claim 36, the at least one circuit being external to the integrated circuit.