Digital isolation system with ADC offset calibration

• US 6,323,796 B1
• Filed: 03/01/2000
• Issued: 11/27/2001
• Est. Priority Date: 04/22/1997
• Status: Expired due to Term

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Scott, Jeffery W., Krone, Andrew W., Welland, David R., Dupuis, Timothy J., Sooch, Navdeep S.
• Primary Examiner(s): Jeanpierre, Peguy
• Assistant Examiner(s): Lauture, Joseph J
• Application Number:
  US09/516,898
• Time in Patent Office: 636 Days
• Field of Search: 341/143, 375/219, 375/259, 375/220, 375/222, 379/399, 379/412, 379/413
• US Class Current: 341/143
• CPC Class Codes: H03M 3/384 Offset correction removal of offset already present on the analogue input signal H03M3/494
• CPC Class Codes: H03M 3/458 Analogue/digital converters using delta-sigma modulation as an intermediate step
• 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 1/573 Line monitoring circuits for detecting caller identification
• 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: H04M 19/02 providing ringing current or supervisory tones, e.g. dialling tone or busy tone

Abstract

A digital capacitive isolation barrier system is provided that is suitable for use in a telephone or modem where the locally powered circuits must be effectively isolated from the public telephone system, while permitting data transfer across the barrier. In particular, an automatic ADC offset calibration system is provided for determining the magnitude of the ADC offset signal required in the system during a calibration operation, and for providing the ADC offset signal during normal operation of the isolation barrier system. Fixed bias signals are also provided for the ADC and for a DAC in the system. In a preferred embodiment, the ADC is located on the isolated side of the isolation barrier, while the integrator and register that determine and hold the offset signal are located on the powered side of the isolation barrier.

Claims

1. An isolation system for providing an isolated telephone line communication channel for digital data signals in a forward direction and in a reverse direction across an isolation barrier comprised of one or more isolation elements, the system comprising:

a plurality of isolation elements which form the isolation barrier, at least some of the isolation elements being isolation capacitors;

a powered system on a first side of the isolation barrier, the powered system coupled to the isolation barrier for driving a forward direction digital signal across the isolation barrier;

an isolated system on a second side of the isolation barrier, the isolated system coupled to the isolation barrier for driving a reverse direction digital signal across the isolation barrier; and

an analog to digital converter located on the second side of the isolation barrier, the analog to digital converter configured to allow offset calibration,

wherein the isolated system receives at least some power transferred from across the isolation barrier for providing a power supply on the second side of the isolation barrier.

2. The system of claim 1 wherein the forward direction digital signal and the reverse direction digital signal are both driven through at least one same isolation capacitor.

3. The system of claim 2 wherein the power transferred across the isolation barrier is transferred across at least one of the isolation capacitors.

4. The system of claim 1, further comprising an analog to digital converter offset calibration system, the analog to digital converter offset calibration system comprising:

an integrator coupled to receive an output signal from the analog to digital converter; and

a digital to analog converter having an output providing an analog offset calibration signal,

wherein the analog offset calibration signal is coupled to an input of the analog to digital converter.

5. The system of claim 4, wherein the digital to analog converter comprises a delta sigma modulator coupled to a one-bit digital to analog converter.

6. The system of claim 5, wherein the delta sigma modulator is located on the first side of the isolation barrier and the one-bit digital to analog converter is located on the second side of the isolation barrier.

7. The system of claim 4, wherein the analog to digital converter is located on the second side of the isolation barrier and the integrator is located on the first side of the isolation barrier.

8. The system of claim 4, wherein the analog to digital converter is a delta-sigma analog to digital converter.

9. The system of claim 4 wherein the forward direction digital signal and the reverse direction digital signal are both driven through at least one same isolation capacitor.

10. A method for providing digital communication across a telephone line isolation barrier, the telephone line isolation barrier comprising at least one isolation capacitor, the method comprising:

transmitting from a first side of the isolation barrier a transmitted digital signal to be communicated across at least one isolation capacitor;

receiving on a second side of the isolation barrier a received digital signal from at least one isolation capacitor;

providing an analog to digital converter on the second side of the isolation barrier;

generating on the second side of the isolation barrier a clock signal, the clock signal generated from information transmitted across the isolation barrier;

generating on the second side of the isolation barrier a power supply, the power supply generated from information transmitted the isolation barrier; and

calibrating the offset of the analog to digital converter.

11. The method of claim 10, wherein the clock signal is generated from information transmitted across at least one isolation capacitor.

12. The method of claim 11, wherein the power supply is generated from information transmitted across at least one isolation capacitor.

13. The method of claim 12 wherein the same isolation capacitor is utilized for generating the clock signal and the power supply.

14. The method of claim 10, wherein the power supply is generated from information transmitted across at least one isolation capacitor.

15. A method claim 10, further comprising:

integrating an output signal from the analog to digital converter to provide an integrated offset calibration signal, and

converting the integrated offset calibration signal from a digital signal to an analog offset calibration signal.

16. The method of claim 15, wherein the analog to digital converter output signal is transmitted across the isolation barrier before it is integrated.

17. The method of claim 16, wherein the analog to digital converter output signal is transmitted across at least one isolation capacitor before it is integrated.

18. The method of claim 17, wherein the integrated offset calibration signal is transmitted across the isolation barrier before it is converted to an analog offset calibration signal.

19. The method of claim 18, wherein the integrated offset calibration signal is transmitted across at least one isolation capacitor before it is converted to an analog offset calibration signal.

20. The method of claim 15, wherein the integrated offset calibration signal is transmitted across the isolation barrier before it is converted to an analog offset calibration signal.

21. The method of claim 20, wherein the integrated offset calibration signal is transmitted across at least one isolation capacitor before it is converted to an analog offset calibration signal.