Digital access arrangement circuitry and method having current ramping control of the hookswitch

• US 6,823,066 B1
• Filed: 07/02/1999
• Issued: 11/23/2004
• 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:
  US09/347,689
• Time in Patent Office: 1,971 Days
• Field of Search: 379/399-1-3
• 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 hookswitch transition for a variety of international phone standards is provided. The invention may also be utilized with means for transmitting and receiving a signal across a capacitive isolation barrier. More particularly, a DAA circuitry may be utilized which satisfies many or all hookswitch transition standards without the use of additional discrete devices. The hookswitch transition standards may be satisfied by ramping down the current flowing through the hookswitch prior to transitioning the hookswitch state. In this manner the hookswitch current change as a function of time (di/dt) may be decreased. Thus, the current through the hookswitch may be actively controlled prior to switching the hookswitch from an off-hook condition to an on-hook condition. By controlling the current drawn from the phone lines through the hookswitch, the maximum voltage seen at the phone company exchange may be decreased.

Claims

1. A communication system, comprising:

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

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

a hookswitch transition node carrying a hookswitch transition signal indicative of a desire to change a hookswitch within the phone line side circuitry from an off-hook state to an on-hook state; and

current control circuitry coupled to the hookswitch transition node within the phone line side circuitry, the current control circuitry operating prior to the completion of a hoolswitch transition to enable a decrease in a current level drawn from the phone line in response to the hookswitch transistion signal.

2. The communication system of claim 1, further comprising at least one switch within a phone line side DAA integrated circuit, the switch being responsive to the hookswitch transition signal to implement at least a portion of the ramping of the current drawn from the phone line.

3. The communication system of claim 2, 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.

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 comprising one or more capacitors.

5. The communication system of claim 1, the hookswitch comprising at least one bipolar transistor.

6. 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.

7. 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.

8. The communication system of claim 7, further comprising the isolation barrier coupled between the phone line side circuitry and the powered side circuitry, the isolation barrier being a capacitive barrier.

9. The communication system of claim 8, the current being ramped downward to a value of less than or equal to 50% of the currents drawn from the phone line prior to a transition in the hookswitch transition signal.

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

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

drawing current at a first current level from the phone line through the hookswitch circuitry;

providing hookswitch circuitry within the phone line side circuitry, the hookswitch circuitry setting the communication system in a phone line off-hook state or a phone line on-hook state; and

adjusting downward the current drawn through the hookswitch to a second level in response to a signal indicative of a desired state of the hookswitch circuitry prior to changing the hookswitch from an off-hook state to an on-hook state, the second current level being less than the first current level.

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, the current being adjusted downward while the hookswitch begins to change states.

16. The method of claim 15, the second current level being less than or equal to 50% of the first current level when the hookswitch has completely changed states.

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

18. A hookswitch transition circuit within a communication system that is capable of being connected to phone lines, the hookswitch transition circuit comprising:

a hookswitch control node carrying a hookswitch control signal to control a hookswitch;

at least one variable current circuit coupled to the hookswitch control node, the at least one variable current circuit responsive to the hookswitch control signal to decrease a current drawn from the phone lines prior to changing the state of the hookswitch; and

at least one switch coupled to the hookswitch control node within a phone line side DAA integrated circuit.

19. The hookswitch transition circuit of claim 18, the at least one variable current circuit comprises at least two variable current circuits, each coupled to the hookswitch control node.

20. The hookswitch transition circuit of claim 18, the hookswitch control signal also initiating a change of state of the hookswitch.

21. The hookswitch transition circuit of claim 18, the at least one variable current circuit being responsive to the hookswitch control signal when the hookswitch control signal indicates a transition from an off-hook state to an on-hook state.

22. The hookswitch transition circuit of claim 18, a current level within the at least one variable current circuit having a first current level when the hookswitch control signal is in an off-hook state and a current level within the at least one variable current circuit having a second level when the hookswitch control signal is in an on-hook state, the second current level being less than the first current level.

23. The hookswitch transition circuit of claim 18, the current drawn from the phone lines being decreased to a second current level that is 50% or less than a first current level, the first current level being an off-hook current level and the second level being attained prior to the hookswitch completing a transition to an on-hook state.

24. A method of controlling current in a phone line, comprising:

actively controlling at least one current circuit of a DAA integrated circuit in response to a hookswitch transition signal; and

substantially decreasing the current in the phone fine as a result of the active control prior to achieving an on-hook state.

25. The method of claim 24, wherein the hookswitch transition signal is indicative of a transition from an off-hook state to an on-hook state.

26. The method of claim 25, wherein the current is decreased by at least 50%.

27. The method of claim 24, wherein the actively controlling further comprises controlling a plurality of current circuits.

28. The method of claim 24, wherein the active control includes changing the state of at least one switch within the DAA integrated circuit.

29. The method of claim 28, wherein the at least one circuit is coupled to the hookswitch.