Analog isolation system with digital communication across a capacitive barrier

• US 6,297,755 B2
• Filed: 02/26/2001
• Issued: 10/02/2001
• Est. Priority Date: 04/22/1997
• Status: Expired due to Term

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Scott, Jeffrey W., Welland, David R., Sooch, Navdeep S.
• Primary Examiner(s): JeanPierre, Peguy
• Application Number:
  US09/792,940
• Publication Number:
  US 20010010502A1
• Time in Patent Office: 218 Days
• Field of Search: 341/110, 341/143, 341/155, 379/399, 379/412
• US Class Current: 341/110
• CPC Class Codes: H04B 14/062 using delta modulation or one-bit differential modulation [1DPCM]
• 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

Abstract

An isolation system is provided that is suitable for use in telephony, medical instrumentation, industrial process control and other applications. Preferred embodiments of the invention comprise a capacitive isolation barrier across which a digital signal is communicated. The system provides a means of communication across the isolation barrier that is highly immune to amplitude and phase noise interference. Clock recovery circuitry may be employed on one side of the isolation barrier to extract timing information from the digital signal communicated across the barrier, and to filter the effects of phase noise introduced at the barrier. Delta-sigma converters may be disposed on both sides of the isolation barrier to convert signals between analog and digital domains. An isolated power supply may also be provided on the isolated side of the barrier, whereby direct current is generated in response to the digital data received across the isolation barrier. Finally, a bidirectional isolation system is provided whereby bidirectional communication of digital signals is accomplished using a single pair of isolation capacitors. In preferred embodiments, the digital data communicated across the barrier consists of digital delta-sigma data signals multiplexed in time with other digital control, signaling and framing information.

Claims

1. Isolation circuitry for communicating analog signal information across an isolation barrier in digital format, comprising:

an analog-to-digital converter having a digital output;

the analog to digital converter having an input connected to an analog signal containing the analog signal information to be communicated across the isolation barrier;

control information, the control information being combined with a digital output signal of the analog-to-digital converter to form a combined signal;

an output, the output configured to couple the combined signal to an isolation barrier comprised of one or more isolation elements; and

a digital-to-analog converter having an input configured to be coupled to an output of the isolation barrier, the digital-to-analog converter providing an analog output signal.

2. The isolation circuitry of claim 1, wherein the analog-to-digital converter and the digital-to-analog converter are synchronized to a common clock signal.

3. The isolation circuitry of claim 1, further comprising the isolation barrier wherein the isolation barrier comprises at least one capacitive isolation element.

4. The isolation circuitry of claim 3, wherein the isolation barrier input and the isolation barrier output are a common isolation barrier input/output and the analog-to-digital converter and the digital-to-analog converter are both located on an isolated side of the isolation barrier.

5. The isolation circuitry of claim 3, wherein the isolation barrier is a bidirectional isolation barrier.

6. The isolation circuitry of claim 5, wherein at least one isolation element may receive information to be driven in a forward and reverse direction.

7. The isolation circuitry of claim 1, further comprising a multiplexer having a first input connected to the digital output of the analog-to-digital converter and a second input connected to receive the control information, wherein the multiplexer is configured to be coupled to the isolation barrier.

8. A telephone line interface circuit comprising the isolation circuitry of claim 1.

9. A method for conveying an analog signal from a transmitting circuit to a receiving circuit while electrically isolating the transmitting circuit from the receiving circuit, comprising:

converting the analog signal to a first digital signal;

transferring the first digital signal to an isolation barrier having at least one capacitive element, the transferring being in a first direction;

receiving a second digital signal in a second direction from the isolation barrier, the transferring of the first digital signal and the receiving of the second digital signal being configured to occur across the same capacitive element; and

converting the transferred second digital signal to an analog output signal.

10. The method of claim 9, further comprising:

combining the first digital signal with at least a third digital signal to form a combined digital signal, the transferring of the first digital signal to the isolation barrier being accomplished by transferring the combined digital signal across the isolation barrier,

wherein the combined digital signal is intended to be separated into the first digital signal and the third digital signal after the combined digital signal is transferred across the isolation barrier, and the third digital signal is intended to control at least a portion of the receiving circuit.

11. A bidirectional isolated circuit for providing an isolated communication channel for data signals in a forward direction and in a reverse direction across an isolation barrier comprised of at least one isolation element, the circuit comprising:

an isolated system on a first side of the isolation barrier, the isolated system comprising an output for driving a reverse direction digital signal across the isolation barrier and the isolated system further being configured to receive a forward direction digital signal from a powered system driven across the isolation barrier from a second side of the isolation barrier,

wherein the forward direction digital signal and the reverse direction digital signal are both driven through the same isolation element.

12. The isolated circuit of claim 11, wherein the at least one isolation element is a capacitor.

13. The isolated circuit of claim 12, wherein the forward direction digital signal comprises the data signals multiplexed with a control signal.

14. The isolated circuit of claim 12, wherein the reverse direction digital signal comprises the data signals multiplexed with a control signal.

15. The isolated circuit of claim 14, wherein the forward direction digital signal comprises the data signals multiplexed with a control signal.

16. A method for conveying a signal across an isolation barrier, comprising:

providing a receiving circuit operable to communicate with a capacitive isolation barrier and a signal source, the receiving circuit configured to be electrically isolated from a transmitting circuit;

utilizing information transmitted across the capacitive isolation barrier to provide a receiving circuit clock within the receiving circuit, the information transmitted across the capacitive isolation barrier including clock information; and

extracting power from the information transmitted across the capacitive barrier to provide a power supply for at least a portion of a phone line side circuitry.

17. The method of claim 16, wherein the information transmitted across the capacitive isolation barrier further comprises data from the signal source.

18. The method of claim 16, wherein circuitry utilized to extract the power from the information is coupled to at least a first input/output node of the receiving circuit, the first node operable to be coupled to at least one capacitor of the capacitive isolation barrier, the clock information also being received through the first node.

19. An isolation system, comprising:

isolated side circuitry operable to communicate digitally with a powered side circuitry, said digital communication comprising a digital data transmitted from a bidirectional first input/output node, the first input/output node being within the isolated side circuitry, the first input/output node capable of communicating with a capacitive isolation barrier;

a clock signal within the isolated side circuitry, the clock signal capable of being generated from information transmitted across the capacitive isolation barrier;

at least one power supply within the isolated side circuitry, the power supply capable of being generated from information transmitted across the capacitive isolation barrier; and

at least one control signal within the isolated side circuitry, the control signal being capable of being transmitted across the capacitive isolation barrier.

20. The isolation system of claim 19, the digital data being transmitted in a pulse density modulation format.

21. The isolation system of claim 20, the control signal being encoded within information capable of being transmitted across the capacitive isolation barrier.

22. The isolation system of claim 21, the control information being encoded within the digital data.

23. The isolation system of claim 22, the power supply and the clock signal capable of being generated from information transmitted through at least one common capacitor of the capacitive isolation barrier.

24. The isolation system of claim 19, the power supply and the clock signal capable of being generated from information transmitted through at least one common capacitor of the capacitive isolation barrier.

25. The isolation system of claim 19, the control signal being encoded within information capable of being transmitted across the capacitive isolation barrier.

26. Isolated circuitry for communicating telephone line analog signal information across an isolation barrier in digital format, the isolated circuitry including phone line side circuitry, the isolated circuitry comprising:

an analog-to-digital converter having a digital output, the analog to digital converter having an input connected to an analog signal containing the telephone line analog signal information to be communicated across the isolation barrier, the isolation barrier comprised of one more capacitive isolation elements;

control information, the control information being combined with a digital output signal of the analog-to-digital converter to form a combined signal, the combined signal capable of being provided to the isolation barrier;

a digital-to-analog converter having an input capable of being coupled to the isolation barrier, the digital-to-analog converter providing an analog output signal to be transmitted to the telephone line; and

a power supply circuit located within the phone line side circuitry, the power supply circuit generating a DC power supply from a digital signal received across at least one of the capacitive isolation elements.

27. The isolated circuitry of claim 26, wherein the analog-to-digital converter and the digital-to-analog converter are synchronized to a common clock signal.

28. The isolated circuitry of claim 26, wherein the power supply circuit is coupled to at least a first node within the phone line side circuitry, clock information being communicated through the first node.

29. The isolated circuitry of claim 28, wherein the isolated circuitry is configured to drive information in a forward direction and receive information in a reverse direction from across the same capacitive isolation element.

30. The isolated circuitry of claim 26, wherein at least one capacitive isolation element may receive information to be driven in a forward and reverse direction.

31. The isolated circuitry of claim 26, further comprising a multiplexer having a first input coupled to the digital output of the analog-to-digital converter, a second input coupled to receive the control information, and an output capable of being coupled to the isolation barrier.

32. The isolated circuitry of claim 26, further comprising at least one clock signal within the phone line side circuitry, the at least one clock signal being generated from clock information transmitted across the isolation barrier.

33. An isolated circuit for communicating analog telephone line signal information across an isolation barrier in digital format, the isolated circuit including phone line side circuitry, comprising:

an analog-to-digital converter having a digital output signal, the analog to digital converter having an input connected to an analog signal containing the analog telephone line signal information to be communicated across the isolation barrier, the isolation barrier comprised of one or more capacitive isolation elements, at least one of the capacitive isolation elements transmitting data in both a forward direction and a reverse direction, the analog-to-digital converter digital output capable of being coupled to the isolation barrier;

a digital-to-analog converter having an input coupled to the phone line side of the isolation barrier, the digital-to-analog converter providing an analog output signal; and

power circuitry located within the phone line side circuitry, the power circuitry configured to be coupled to the isolation barrier and providing a power supply for at least a portion of the phone line side circuitry by utilizing information transmitted across the isolation barrier.

34. The isolated circuit of claim 33, wherein the analog-to-digital converter and the digital-to-analog converter are synchronized to a common clock signal.

35. The isolated circuit of claim 33, wherein at least some of the transmitting data in both the forward direction and the reverse direction comprises transmitting control information combined with digital data.

36. The isolated circuit of claim 33, wherein at least some of the information transmitted across at least one of the capacitive isolation elements comprises control information combined with the digital output signal.

37. The isolated circuit of claim 33, the power supply and a phone line side clock signal being generated from information transmitted through at least one common capacitor of the capacitive isolation barrier.

38. A method for conveying telephone line signals between a phone line side circuit and a powered side circuit while electrically isolating the phone line side circuit from the powered side circuit, comprising:

providing a first digital signal in the phone line side circuit;

transferring in a first direction the first digital signal to a capacitive isolation barrier having at least one capacitive element, the capacitive isolation barrier providing telephone line isolation;

receiving a second digital signal in a second direction from the isolation barrier, the transferring of the first digital signal and the receiving the second digital signal being through the same capacitive element; and

utilizing at least one signal transmitted received from the capacitive isolation barrier to provide a power supply for at least a portion of the phone line side circuitry.

39. The method of claim 38, further comprising:

combining the first digital signal with at least a third digital signal to form a combined digital signal, the transferring of the first digital signal across the capacitive isolation barrier being accomplished by transferring the combined digital signal across the isolation barrier;

separating the combined digital signal into the first digital signal and the third digital signal after the combined digital signal is transferred across the capacitive isolation barrier; and

utilizing the third digital signal to control at least a portion of the powered side circuit.

40. The method of claim 39, wherein the at least one signal includes clock information.

41. The method of claim 40, further comprising generating a clock signal within the phone line side circuit from the at least one signal.

42. The method of claim 38, wherein the at least one signal includes clock information.

43. The method of claim 42, further comprising generating a clock signal within the phone line side circuit from the at least one signal.

44. The method of claim 38, the at least one signal being the second digital signal.

45. A bidirectional isolated circuit for providing an isolated communication channel for communicating telephone line data signals in a forward direction and in a reverse direction across an isolation barrier comprised of at least one capacitive isolation element, the circuit comprising:

an isolated system on a phone line side of the isolation barrier, the isolated system comprising an output for driving a reverse direction signal across the isolation barrier and an input for receiving a forward direction signal from the isolation barrier; and

a power supply circuit located within the isolated system, the power supply circuit generating a DC power supply from a signal received from the capacitive isolation barrier,

wherein the forward direction signal and the reverse direction signal are both driven and received through the same node of the isolated system so that forward and reverse signals are configured to be provided through the same capacitive isolation element.

46. The isolated circuitry of claim 45, wherein the forward direction signal comprises digital telephone line data signals multiplexed with a control signal.

47. The isolated circuitry of claim 46, an isolated system clock signal also being generated from the digital signal received from across the capacitive isolation barrier.

48. The isolated circuitry of claim 45, wherein the reverse direction signal comprises digital telephone line data signals multiplexed with a control signal.

49. The isolated circuitry of claim 48, an isolated system clock signal also being generated from the digital signal received from across the capacitive isolation barrier.

50. The isolated circuitry of claim 48, wherein the forward direction signal comprises digital telephone line data signals multiplexed with a control signal.

51. The isolated circuitry of claim 50, an isolated system clock signal also being generated from the digital signal received from across the capacitive isolation barrier.

52. A method for provided a signal for use with a phone line, the signal provided from a transmitting circuit to a receiving circuit while electrically isolating the transmitting circuit from the receiving circuit, the method comprising:

providing a first digital signal within the transmitting circuit;

transferring the first digital signal to an isolation barrier having at least one capacitive element, the transferring being in a first direction; and

receiving a second digital signal in a second direction from the isolation barrier, the transferring of the first digital signal and receiving of the second digital signal being across the same capacitive element.

53. The method of claim 52, further comprising:

combining the first digital signal with at least a third digital signal to form a combined digital signal, the transferring of the first digital signal to the isolation barrier being accomplished by transferring the combined digital signal to the isolation barrier,

wherein the third digital signal is provided to be utilized to control at least a portion of the receiving circuit.

54. A bidirectional circuit for providing a communication channel for data signals in a forward direction and in a reverse direction across an isolation barrier comprised of at least one isolation element, the system comprising:

a powered system on a first side of the isolation barrier, the powered system comprising an output driving a forward direction digital signal across the isolation barrier and an input configured to receive an isolated system reverse direction digital signal driven across the isolation barrier from a second side of the isolation,

wherein the forward direction digital signal and the reverse direction digital signal are both driven through the same isolation element.

55. The circuit of claim 54, wherein the at least one isolation element is a capacitor.

56. The circuit of claim 55, wherein the forward direction digital signal comprises the data signals multiplexed with a control signal.

57. The circuit of claim 55, wherein the reverse direction digital signal comprises the data signals multiplexed with a control signal.

58. The circuit of claim 57, wherein the forward direction digital signal comprises the data signals multiplexed with a control signal.

59. A method for conveying a signal across an isolation barrier, comprising:

providing transmitting circuit operable to communicate with a capacitive isolation barrier and a signal source, the transmitting circuit being electrically isolated from a receiving circuit;

providing information from a first node of the transmitting circuit to the capacitive isolation barrier to provide a receiving circuit clock within the receiving circuit, the information provided to the capacitive isolation barrier including clock information; and

wherein the information provided from the first node of the transmitting circuit to the capacitive barrier is also utilized to provide a power supply for at least a portion of the receiving circuit.

60. The method of claim 59, wherein the information provided to the capacitive isolation barrier further comprises data from the signal source.

61. A telephone line isolation system, comprising:

powered side circuitry operable to communicate digitally with isolated side circuitry, said digital communication comprising digital data transmitted from a bidirectional first input/output node, the first input/output node being within the powered side circuitry, the first input/output node configured to communicate with a capacitive isolation barrier;

a clock signal within the powered side circuitry, the clock signal capable of being transmitted to the capacitive isolation barrier; and

at least one control signal within the powered side circuitry, the control signal being capable of being transmitted to the capacitive isolation barrier,

wherein the powered side circuitry is configured to provide power to the isolated side circuitry through the capacitive isolation barrier so that a power supply is capable of being generated within the isolated side circuitry.

62. The isolation system of claim 61, the digital data being transmitted in a pulse density modulation format.

63. The isolation system of claim 62, the control signal being encoded within information capable of being transmitted across the capacitive isolation barrier.

64. The isolation system of claim 63, the control information being encoded within the digital data.

65. The isolation system of claim 63, the power and the clock signal being transmitted through at least one common capacitor of the capacitive isolation barrier.

66. The isolation system of claim 61, the power and the clock signal being transmitted through at least one common capacitor of the capacitive isolation barrier.

67. The isolation system of claim 61, the control signal being encoded within information capable of being transmitted across the capacitive isolation barrier.

68. A method for conveying telephone line signals between a phone line side circuit and a powered side circuit while electrically isolating the phone line side circuit from the powered side circuit, comprising:

providing a first digital signal in the powered side circuit;

transferring in a first direction the first digital signal to a capacitive isolation barrier having at least one capacitive element, the capacitive isolation barrier providing telephone line isolation;

receiving a second digital signal in the powered side circuit in a second direction from the isolation barrier, the transferring of the first digital signal and the receiving of the second digital signal being across the same capacitive element; and

transmitting at least one signal from the powered side circuit to the capacitive isolation barrier to provide power for generating a power supply for at least a portion of the phone line side circuitry.

69. The method of claim 68, further comprising:

combining the first digital signal with at least a third digital signal to form a combined digital signal, the transferring of the first digital signal to the capacitive isolation barrier being accomplished by transferring the combined digital signal across the isolation barrier,

wherein the third digital signal provides control information.

70. The method of claim 69, wherein the at least one signal includes clock information.

71. The method of claim 68, wherein the at least one signal includes clock information.

72. The method of claim 68, the at least one signal being the first digital signal.

73. A bidirectional communication system for conveying telephone line data signals between an isolated circuit and a powered circuit while electrically isolating the powered circuit from the isolated circuit, the system comprising:

an isolation barrier including at least a first isolation capacitor, the first isolation capacitor capable of providing at least some of the isolation between the powered circuit and the isolated circuit; and

the powered circuit, the powered circuit comprising,

a powered circuit input, wherein an input signal at the powered circuit input is the data signal to be transmitted across the first isolation capacitor, and

a powered circuit input/output node coupled to a first side of the isolation capacitor, wherein an output signal at the powered circuit input/output node is a first digital signal to be transmitted across the isolation capacitor in a first direction and wherein an input signal at the powered circuit input/output node is a second digital signal transmitted across the isolation capacitor in a second direction,

wherein the powered circuit is configured to provide power to the isolation barrier from which a power supply is capable of being generated in the isolated circuit.

74. The system of claim 73, further comprising a second isolation capacitor, wherein the digital signals passed across the first and second capacitors are differential signals.

75. The system of claim 73, the powered circuit is configured to provide the power and a clock information through at least one common element of the isolation barrier.

76. Bidirectional circuitry for providing a communication channel for communicating telephone line data signals in a forward direction and in a reverse direction across an isolation barrier comprised of at least one capacitive isolation element, the system comprising:

a powered system on a first side of the isolation barrier, the powered system comprising an output driving a forward direction signal to the isolation barrier and an input for receiving a reverse direction signal from the isolation barrier,

wherein the forward direction signal and the reverse direction signal are both driven through the same capacitive isolation element, and

wherein the powered system is configured to provide power to the isolation barrier so that a DC power supply may be generated within an isolated system from a signal transmitted to the isolation barrier from the powered system.

77. The bidirectional circuitry of claim 76, wherein the forward direction signal comprises digital telephone line data signals multiplexed with a control signal.

78. The bidirectional circuitry of claim 77, wherein a system clock signal is also provided in the forward direction signal.

79. The bidirectional circuitry of claim 76, wherein the reverse direction signal comprises digital telephone line data signals multiplexed with a control signal.

80. The isolation system of claim 79, wherein the forward direction signal comprises digital telephone line data signals multiplexed with a control signal.

81. The isolation system of claim 80, wherein a system clock signal is also provided in the forward direction signal.